By
August 19, 2005
Street Lighting Best Practices
Prepared by:
Kevin J. Mara, P.E.
Braxton Underwood, P.E.
John Pasierb
Hi-Line Engineering, LLC
1850 Parkway Place, Suite 800
Marietta, GA 30067
With contributions from:
Michele McColgan, Ph.D.
Peter Morante
Lighting Research Center
Rensselaer Polytechnic Institute
21 Union St.
Troy, NY 12180
For
American Municipal Power- Ohio
2600 Airport Drive
Columbus, OH 43219
TABLE OF CONTENTS
TABLE OF CONTENTS ............................................................................................................................................ I
TABLE OF FIGURES ............................................................................................................................................. III
I.
INTRODUCTION..............................................................................................................................................1
II.
EXECUTIVE SUMMARY................................................................................................................................2
ILLUMINATION LEVELS .............................................................................................................................................2
Priorities ..............................................................................................................................................................2
Pedestrian Conflict Areas ....................................................................................................................................2
Safety....................................................................................................................................................................2
Security ................................................................................................................................................................2
Design of Roadway Lighting................................................................................................................................3
Consequences of Roadway Lighting ....................................................................................................................3
PROPER CODE SELECTION AND IMPLEMENTATION ....................................................................................................3
NEC & NESC.......................................................................................................................................................3
OSHA Requirements ............................................................................................................................................4
Department of Transportation .............................................................................................................................4
WIRING AND CONSTRUCTION STANDARDS ................................................................................................................5
FIXTURE TYPES .........................................................................................................................................................5
Flood Lights.........................................................................................................................................................5
Cobra Head..........................................................................................................................................................5
Other Fixtures......................................................................................................................................................5
NESC GROUNDING REQUIREMENTS .........................................................................................................................6
Use of System Neutral to Effectively Ground Street Light Poles and Mast Arms ................................................6
Street Lighting Utilization Voltages.....................................................................................................................7
METHODS OF CONTROL OF STREET LIGHTING CIRCUITS ...........................................................................................7
OPERATION AND MAINTENANCE PLAN......................................................................................................................8
Group Relamping.................................................................................................................................................8
Street Light Inventory ..........................................................................................................................................8
Annual Maintenance Cost....................................................................................................................................8
Street Light Poles.................................................................................................................................................8
Dedicated Street Light Wiring .............................................................................................................................8
Street Light Fixture Maintenance and Repair......................................................................................................9
Low Capital Cost Street Light Fixtures (cobra heads) ........................................................................................9
High Capital Cost Street Light Fixtures (decorative post tops, etc.) ...................................................................9
SPOT RELAMPING VERSUS GROUP RELAMPING .........................................................................................................9
SAFETY INSPECTION CHECKLIST ...............................................................................................................................9
OPERATIONS AND MAINTENANCE CHECKLIST ........................................................................................................10
SUMMARY ...............................................................................................................................................................11
III.
ILLUMINATION LEVELS .......................................................................................................................12
PRIORITIES FOR STREET LIGHTING ..........................................................................................................................12
PEDESTRIAN CONFLICT AREAS................................................................................................................................12
SAFETY ....................................................................................................................................................................12
SECURITY ................................................................................................................................................................13
DESIGN OF ROADWAY LIGHTING .............................................................................................................................13
EFFICIENT TECHNOLOGIES ......................................................................................................................................13
APPROPRIATE POLE HEIGHTS ..................................................................................................................................13
APPROPRIATE POLE SPACING ..................................................................................................................................14
CONSEQUENCES OF ROADWAY LIGHTING ...............................................................................................................14
RECOMMENDATIONS ...............................................................................................................................................15
Pedestrian Conflict Areas ..................................................................................................................................15
Illumination Levels and Roadway Classifications .............................................................................................15
Design of Roadway Lighting..............................................................................................................................16
I
Consequences of Roadway Lighting ..................................................................................................................16
AASHTO’S CLASSIFICATION OF ROADWAYS, WALKWAYS, AND AREAS ...............................................................20
Roadway and Walkway Classifications .............................................................................................................20
Area Classifications ...........................................................................................................................................20
ANSI/IESNA’S ROADWAY, PEDESTRIAN WALKWAY, AND BIKEWAY CLASSIFICATIONS ......................................21
PEDESTRIAN CONFLICT AREA CLASSIFICATIONS.....................................................................................................22
IV.
PROPER CODE SELECTION AND IMPLEMENTATION .................................................................24
WHICH CODE APPLIES TO MUNICIPAL STREET LIGHTS? .........................................................................................25
CASE STUDIES FOR PROPER APPLICATION OF ELECTRICAL CODES .........................................................................26
OSHA REQUIREMENTS ...........................................................................................................................................27
DEPARTMENT OF TRANSPORTATION........................................................................................................................28
V.
WIRING AND CONSTRUCTION STANDARDS .......................................................................................30
NESC GROUNDING REQUIREMENTS .......................................................................................................................31
USE OF SYSTEM NEUTRAL TO EFFECTIVELY GROUND STREET LIGHT POLES AND MAST ARMS .............................33
STREET LIGHTING UTILIZATION VOLTAGES ............................................................................................................35
VI.
METHODS OF CONTROL OF STREET LIGHTING CIRCUITS......................................................37
PHOTOCELLS ...........................................................................................................................................................37
MONITORING AND CONTROL SYSTEMS ...................................................................................................................38
VII.
OPERATION AND MAINTENANCE PLAN – PRACTICES DETERMINED FROM SURVEY
CONDUCTED BY LRC ...........................................................................................................................................40
STREETLIGHT POLES ...............................................................................................................................................40
DEDICATED STREETLIGHT WIRING..........................................................................................................................40
STREETLIGHT FIXTURE MAINTENANCE AND REPAIR ...............................................................................................41
LOW CAPITAL COST STREETLIGHT FIXTURES (COBRA HEADS)................................................................................41
HIGH CAPITAL COST STREETLIGHT FIXTURES (DECORATIVE POST TOPS, ETC.) .......................................................41
RECOMMENDATIONS ...............................................................................................................................................41
SPOT RELAMPING VERSUS GROUP RELAMPING .......................................................................................................42
SAFETY INSPECTION CHECKLIST .............................................................................................................................45
OPERATION AND MAINTENANCE CHECKLIST ..........................................................................................................46
APPENDIX A ............................................................................................................................................................49
APPENDIX B.............................................................................................................................................................85
APPENDIX C ............................................................................................................................................................91
UNDERSTANDING GROUNDING ................................................................................................................................96
APPENDIX D ..........................................................................................................................................................101
TRAINING PREREQUISITE .......................................................................................................................................103
SEMINAR GOALS ...................................................................................................................................................103
TRAINING OBJECTIVE ............................................................................................................................................103
TERMINAL OBJECTIVES .........................................................................................................................................104
TRAINING STRATEGIES ..........................................................................................................................................104
TRAINING CURRICULUM ........................................................................................................................................106
BIBLIOGRAPHY ...................................................................................................................................................109
II
TABLE OF FIGURES
Figure 1 Angles referenced by the IESNA Cutoff Classifications ............................................... 15
Figure 2 Touch Potential Concerns................................................................................................. 1
Figure 3 Touch Potential Concerns Hand to Hand Contact.......................................................... 34
Figure 4 Bonding of Street Light Pole to a Fence ........................................................................ 35
Figure 5 Effects of Electricity on Humans ................................................................................... 95
Figure 6 Example Circuit, Equipment Case Remotely Grounded................................................ 97
Figure 7 Example Circuit, Equipment Case Bonded to System Neutral ...................................... 98
Figure 8 Example Circuit, Equipment Case Remotely Grounded and Bonded to System Neutral
............................................................................................................................................... 99
III
I.
INTRODUCTION
Lighting of our roadways and pedestrian areas is employed everywhere to conserve human life
and reduce the risk of injury while also protecting property. The proper implementation of
lighting designs is essential in obtaining these goals to preventing unnecessary exposure of the
public to hazardous conditions. The American Public Power Association, at the request of
American Municipal Power – Ohio and City of Columbus, Ohio Division of Electricity,
chartered the completion of this report to help define the best practices in street lighting. Hi-Line
was engaged as the prime contractor in development of this report with assistance from Lighting
Research Center at Rensselaer Polytechnic Institute. With a combined experience level greater
than forty years, the report authors from Hi-Line consisted of: Kevin J. Mara, P.E., Braxton J.
Underwood, P.E., and John Pasierb. Key personnel for the Lighting Research Center were
Michele McColgan, Ph.D. and Peter Morante.
The purpose of Street Lighting Best Practices is to: interpret and specify the proper
implementation of electrical code requirements (National Electric Code or National Electrical
Safety Code) for differing street lighting systems, identify various roadway categories, and
provide a curriculum for training individuals responsible for inspecting and approving new street
lighting construction. Included in the identification of various roadway categories is a survey of
the best practices used in street lighting. The survey provides: proper illumination levels, correct
pole wiring design, and construction standards for the rehabilitation of existing and new
construction of underground street lighting systems. Also included are recommendations for
streetlight operation and maintenance guidelines.
Emphasis of this report is placed on heightening awareness of advantages and disadvantages
provided by different lighting designs and how different designs impact system operations. In
addition to impacts on system operations, the report names possible hazards exposed to the
public. A discussion of grounding and bonding is included, allowing utilities a chance to
examine advantages and disadvantages offered by distinct methods or combinations of methods.
This report attempts to guide utilities, and other parties owning street-light systems, to develop
safe and effective street lighting designs and practices.
1
II.
EXECUTIVE SUMMARY
Street Lighting Best Practices is an effective tool designed to identify main areas of concern for
utilities and entities involved in street-light design, maintenance, and operation. From these
areas of concern, suggested practices are recommended based upon survey responses and
industry practices. This summary will provide a quick reference to significant recommendations
in each area of concern.
Illumination Levels
Priorities
There are numerous priorities existing for making street lighting decisions. It is important to
recognize that not all priorities are based on safety and security. When making street lighting
decisions, societal goals, economic development, and illumination of set area are each valid
arguments for street light placement.
Pedestrian Conflict Areas
Vehicle-pedestrian interaction is responsible for a disproportionate amount of nighttime
fatalities. The magnitude of pedestrian flow is almost always related to the abutting land use.
Low, medium and high are three classifications of pedestrian night activity levels and types of
land use are. Areas with very low volumes of night pedestrian usage are assigned the ‘low’
classification. Areas where lesser numbers of pedestrians utilize the streets at night are classified
‘medium’. Areas expecting significant numbers of pedestrians to use sidewalks or crosswalks
during dark are classified ‘high’. The survey and research showed that the American
Association of State Highway and Transportation Officials (AASHTO) definition and
terminology was used for the determination of classifications. Further, the areas were lit in
accordance with AASHTO recommendations based upon the classification.
Safety
Street lighting provides more than just illumination of roadways. Adjacent areas such as
walkways and yards benefit from street lighting as well. This illumination provides the extra
benefit of safety for pedestrians, cyclists, and children. With pedestrian areas lit, drivers see
these groups sooner, possibly avoiding a fatal collision.
Security
In addition to safety, street lighting can produce a sense of security. People feel safer more
secure walking in a well lit area. The incident of crime in a well lit area is likely to be less than
that of a poorly or unlit area, as delinquents prefer cover of dark. In order for security lighting to
be effective, minimum light levels providing objectives of brightness and uniformity must be
achieved. These light levels are recommended by AASHTO.
2
Design of Roadway Lighting
Proper illumination levels on roadways are paramount when considering driver safety. Proper
positioning of lights on roadways will help provide consistent and even lighting, providing
drivers with increased visibility. Appropriate pole height and spacing allow for consistent and
even lighting. Proper mating of fixtures to pole height also contributes to consistent lighting
patterns. AASHTO “Information Guide for Roadway Lighting” and ANSI/IESNA RP-8-00 are
two sources of information for proper lighting of roadways. The survey found most terminology
follows that of AASHTO and the terminology used by IESNA is synonymous.
Consequences of Roadway Lighting
When designing roadway lighting, negative impacts should be minimized. Light trespass is an
important negative impact that should be avoided. Light trespass can be minimized by: using the
minimum light levels to meet the lighting objective, choosing light fixtures which are cutoff and
full cutoff minimizing uplight and glare, and considering the impact on adjacent properties when
placing lights.
Proper Code Selection and Implementation
Street lighting must be designed to meet lighting levels while complying with the applicable
safety codes. Selection of the appropriate code should be determined based on the type of
personnel who are operating the system.
NEC & NESC
Two primary codes are used in the United States; the National Electrical Code (NEC) and the
National Electrical Safety Code (NESC). California, however, uses its own code for utilities;
California Public Utilities Commission General Order 95 and General Order 128. These General
Orders apply to those utilities under the jurisdiction of the Public Utilities Commission, State of
California.
The major distinction between NEC and NESC is the style in which the codes are written. The
NESC is a performance-based code while the NEC is a prescriptive-based code. A performance
base code provides rules for how a system should perform, but does not provide details on how
to achieve this performance.
This difference in the style of the codes leads to confusion when comparing design options for
street lighting systems. The NESC method leaves design decisions to the engineer, who is
responsible for complying with the performance standards. The NEC provides explicit rules for
the design, which if followed, achieve the NEC’s safety objectives.
3
The NESC applies to utilities, public and private, provided the street lighting is in exclusive
control of the utility. In a case where convenience outlets are installed for special lighting
(Christmas lights) and the outlets can be reached by a non qualified person, the outlets must
conform to the NEC. If a municipality without an electric utility installs streetlights, it must
comply with the NEC. Review of the case studies better illustrates safety code requirements.
OSHA Requirements
In addition to the safety codes for the design of the street lighting system, Occupational Safety
and Health Administration (OSHA) requirements are applicable. OSHA requirements are geared
towards personnel operating and maintenance of the street lighting system. OSHA defines who
can work on these systems and what requirements are necessary for their protection. OSHA’s
protection of workers from electrical hazards is broken into two parts. OSHA standards subpart
S of the General Industry Standards address electrical utilization systems, i.e., installations of
electric conductors and equipment which use electric energy for mechanical, chemical, heating,
lighting, or similar purposes. Subpart S protects most employees from the hazards associated
with electric utilization equipment and with premises wiring. Subpart S would apply to
electricians working on premises wiring which include area lightning. Further, subpart S relates
more to the electrical systems covered by the NEC since the hazards are associated with
utilization equipment. It should be noted, not all municipalities fall under OSHA control.
OSHA developed 29 CFR 1910.269 that focuses on the operation and maintenance of electric
power transmission and distribution systems. OSHA also states only qualified persons may work
on or with exposed energized lines or parts of equipment operating at 50 volts or more. OSHA
defines a qualified person as one knowledgeable in the construction and operation of the electric
power generation, transmission, and distribution equipment involved, along with the associated
hazards.
Department of Transportation
Each state adopts its own requirements with regards to safety within the rights-of-way of their
state and county roads. These requirements are typically based on the recommendation
contained in the following documents;
ƒ “An Information Guide for Roadway Lighting, American Association of State
Highway and Transportation Officials (AASHTO)
ƒ “Report 152 – Warrants for Highway Lighting, National Cooperative Highway
Research Program (NCHRP)
ƒ “American National Standard Practice for Roadway Lighting (ANSI/IESNA RP8-00), Illuminating Engineering Society of North America in ANSI Practice for
Roadway Lighting ANSI RP-8)
In general, all ground mounted luminaire supports exposed to traffic and located within the clear
zone should be provided with breakaway or yielding bases, unless they are located with the
protection of a barrier (An Informational Guide for Roadway Lighting AASHTO 1984).
AASHTO Roadside Design Guide, 3-6 (2002) defines the clear zone based on vehicle speed,
4
average daily traffic, and shoulder slopes. AASTHO recommends that efforts should be made in
all breakaway poles that house electrical components to effectively reduce fire and electrical
hazards posed after structure impact.
The AASHTO publication Standard Specifications for Structural Supports for Highway Signs,
Luminaries, and Traffic Signals, 2001 provide standards for breakaway poles. This document
states that breakaway supports shall be designed to yield, fracture or separate when struck by an
errant vehicle. Other sources of information on breakaway poles are Recommended Procedures
for Safety Performance Evaluation of Highway Features and AASHTO’s Roadside Design
Guide.
Wiring and Construction Standards
The purpose of construction standards is to provide drawings and specifications that apply to
repetitive installations. This enables safety, reliability, operability, uniformity, appearance, and
economy to be coordinated in the system’s construction practices.
Fixture Types
Fixtures utilized depend on the task lighting requirements and aesthetics. Some utilities define
the types of system by assigning particular fixture wattage to categories of street lighting. One
utility defines a 70 watt fixture as an alley light, a 100 watt fixture as a local light, a 150 watt
fixture as a collector light, and a 250 watt fixture as a major light. However, this is not typically
the norm. Most utilities consider anything 100 watts or below as a security light and anything
above as a street or area light.
Flood Lights
Flood lights used by utilities are typically 400 watt or 1000 watt high pressure sodium fixtures.
They are utilized when high intensity illumination of a specific non-roadway area is needed. The
most common utilization voltages seen are 120 or 240 volts.
Cobra Head
The most common fixture used for a roadway luminaire is a cobra head fixture. Typical sizes are
150, 250, and 400 watt. The mounting heights and types vary; typically one can expect to see
the cobra head fixture mounted between 30 to 37 feet above the roadway. Most utilities
purchase and maintain a stock of high pressure sodium vapor fixtures. Other utilities currently
using mercury vapor fixtures are planning to convert to the more efficient and cost effective high
pressure sodium vapor fixture. These fixtures are typically available as drop prismatic refractor
glass, flat glass, short semi- cutoff, medium semi- cutoff, medium cutoff, and full cutoff.
Other Fixtures
Other fixtures utilized, but not as prevalent, are high mast and teardrop fixtures. These have a
more specialized application in roadway lighting. The high mast luminaire is ideal for use on
interstate highways or large areas requiring maximum pole spacing. The teardrop fixture is used
for a more 1930’s nostalgic look, providing a style of yesteryear while also being energy
5
efficient. Decorative fixtures are utilized for street lighting as well, however they are typically
confined to downtown areas or housing subdivisions. A typical style of decorative light
employed by utilities is the Acorn fixture.
NESC Grounding Requirements
The NESC provides rules on grounding of components as a means to safeguard any person from
injury that could be caused by electrical potential. The rules on grounding can be found in
Section 9, Grounding Methods for Electric Supply and Communication Facilities, of the NESC
2002 edition. There are two purposes for protective grounding;
1. Enhanced operation of system overcurrent protective devices
2. Minimize exposure of personnel to electrical potential
In Rules 215C1 and 314B, the NESC requires that certain metal supporting structures, including
lamp posts, be effectively grounded. It should be noted that these rules do not apply as long as
the voltage is less than 300 volts. However, when the voltage does exceed 300 volts, to comply
with this performance requirement, it is necessary to understand the definition of “effectively
grounded.” In Section 2 of the NESC, the definition of effectively grounded is given as
“intentionally connected to earth through a ground connection or connections of sufficiently low
impedance and having sufficient current-carrying capacity to limit the buildup of voltages to
levels below that which may result in undue hazard to persons or to connected equipment.”
Use of System Neutral to Effectively Ground Street Light Poles and Mast Arms
During normal operation, the current flow in the neutral will cause a voltage drop and therefore a
potential difference may appear at the metal pole. This voltage rise will be less than 4 volts and
not perceptible to humans. The grounded circuit conductor (neutral) is used to ground a metal
street light pole or mast arm.
If a short occurs between the hot leg and the metal pole there are two paths for the fault current
back to its source. One path is through the system neutral conductor. The other path is through
the individual’s hand, out his feet, and through the earth. The current division is based on the
ratio of resistances of the two paths. The path to ground may not always involve contact through
an individuals hand and out his foot.
If the system neutral impedance, from the pole back to the source, is much less than the
resistance of the body and the ground resistance at the person’s feet or other contact point, then
the pole would be effectively grounded.
NESC Rule 350F alludes to bonding all above ground metallic equipment that is separated by
less than 6 feet. Bonding these objects reduces the potential difference for metal-to-metal touch
potential. Refer to this section and Appendix C for a more detailed discussion of touch potential.
6
Street Lighting Utilization Voltages
Electrical energy losses are reduced at higher voltages, however, past 300 volts, rules from the
National Electrical Safety Code (NESC) begin to apply. In order to operate efficiently, one must
strike the proper balance of voltage levels, acceptable electrical losses, and the amount of
regulation you must contend with. The Lighting Research Center of Rensselaer Polytechnic
Institute (LRC) survey performed for this report shows a majority of utilities use a 120 volt street
lighting system (62%) followed by a 240 volt street lighting system (28%). Street lighting
system voltages of 480 volts (7%) and 277 volts (3%) are less frequently used.
Most utilities distribution practices include stringing 120/240 volt service wire along the
roadways to service customers. Rather than running a second set of wires, and using a different
voltage, utilities will generally tap the existing 120/240 volt service wire for the street lighting
instead. Another factor is the cost differential between the common 120/240 volt and 480 volt
transformers.
Another reason that 120/240 volt service is selected over 480 volt service is the increased
likelihood of electrocution if a person comes in direct contact with the wire. Typical skin
resistance permits a current flow of approximately 0.024 to 0.080 amperes if a person touches a
120 volt conductor. This may be enough to cause fibrillation given sufficient time. However,
the current flow would be 0.096 to 0.320 amps if a person touches a 480 volt conductor, resulting
in a much higher likelihood of fibrillation.
One final consideration is the additional code compliance requirements. Those utilities governed
by the NESC will need to comply with performance based rules 215C1 and 314B. These require
that certain metal supporting structures, including lamp posts, must be effectively grounded.
These rules apply only to street lighting systems greater than 300 volts. Utilities operating at 480
volts would thus be required to comply with these extra performance based rules.
Based upon the survey results, common utility practices indicate the use of either a 120 or 240
volt service for street lighting as a best practice.
Methods of Control of Street Lighting Circuits
Photocells have and continue to be the most common method of street and floodlight control in
the electric utility industry. Based on a survey conducted for this document by the LRC,
photocells are utilized in 82% of lighting installations.
Photocells can be used in conjunction with external relays to energize multiple lights at the same
time, often called a master control. This is accomplished utilizing a circuit dedicated to street
lighting. The line is energized only when the photocell actuates the relay. According to the
survey, only 17% of respondents utilize this means of control. Utilities tend to use photocells
more frequently (83% for Municipal Utilities and 87% for Investor Owned Utilities) than
municipally owned street lighting (68%). The use of master controllers for street lighting is
7
mainly used by municipalities that own street lighting systems and accounts for a much smaller
portion of the overall control of street lighting (17%).
Operation and Maintenance Plan
Nearly half of the survey respondents (48%) report that maintenance of streetlights is performed
by dedicated streetlight crews. Contractors perform this function 26% of the time and 26% of
the time it is performed by regular line crews. The use of high voltage linemen to perform
streetlight maintenance was reported by 50% of respondents. However, municipalities that own
streetlights are more likely to use low voltage line personnel.
Group Relamping
Group relamping is only used by 38% of the respondents. All survey respondents indicated that
streetlight fixtures, poles and wiring are only replaced upon failure.
Street Light Inventory
Inventories of streetlights in use are conducted by 71% of the survey respondents either as part of
any group relamping or conducted as separate inventories. Streetlight outage reporting is
predominately provided by customers (55%) and by police and a dedicated person within the
streetlight owning entity (21% each).
Annual Maintenance Cost
The annual maintenance cost per streetlight as reported in the survey varies greatly from a low of
$10 to a high of $400. The most likely costs for entities not conducting group relamping is
approximately $40.
Street Light Poles
As stated above, all survey respondents indicated they only replace streetlight poles upon failure.
This practice is recommended. Inspection of any wood streetlight only poles should occur at the
same inspection interval as wood overhead line poles.
Dedicated Street Light Wiring
The vast majority of survey respondents (79%) indicated they do not perform any streetlight
wiring inspections. Streetlight wiring is only replaced upon failure according to all survey
respondents. Replacement of only failed streetlight wiring is the recommendation set forth here,
with a noted exception. Certain types of underground/direct buried electrical wires are known to
deteriorate more rapidly than their original specifications.
8
Street Light Fixture Maintenance and Repair
All survey respondents indicated they only replace streetlight fixtures upon failure of the fixture.
It is believed this is a sound economic and safety policy. Therefore, it is recommended that
streetlight fixtures only be replaced upon their failure.
Low Capital Cost Street Light Fixtures (cobra heads)
The recommended definition of failure for these fixtures is anything that fails beyond lamps,
photocells and the glass globe. Replacing/repairing ballasts and other electrical components may
cost (parts and labor) more than replacing a low cost fixture.
High Capital Cost Street Light Fixtures (decorative post tops, etc.)
All efforts should be made to repair the higher cost streetlight fixtures. Replacement of ballasts,
lenses, glass, photocells, etc. will be less costly than replacing the entire fixture.
Spot Relamping versus Group Relamping
Spot Relamping is defined as fixing lighting lamps only when they are broken. This program is
usually dependent on drive by inspections at night or consumer/police outage reports. Group
Relamping is defined as replacing lamps on a periodic replacement schedule or “best time
schedule”. A group relamping program is usually defined by area within a system and is largely
influenced by the luminaire life curves provided by lamp manufacturers. A “best time schedule”
is based on when the total cost of energy use, cost of installation, and relamping is at its
minimum. Effectiveness less than 50% is a good indicator while 33% to 25% of lamp life
remaining offers a good mix as well.
The survey not withstanding, it is recommended that group relamping be pursued. All economic
studies on this subject show potential savings by using group relamping. The Illuminating
Engineering Society of North America (IESNA) design guide DG-4-03, Design Guide for
Roadway Lighting Maintenance, illustrates an analysis of spot versus group relamping. A
review of their assumed costs shows them to be reasonable. The use of the non-cycling,
environmentally friendly HPS lamp will further improve the economics of group relamping
because of the extended life of these lamps. The group relamping schedule can be stretched
from four years to five years.
Safety Inspection Checklist
Developing a proper safety inspection checklist for street lighting maintenance is very important
to maintain adequate safety levels and reliability. An excellent guideline for safety inspection is
the California Public Utility Commission’s General Order #95, which outlines requirements for
street and decorative lighting.
9
The following timetable for inspection is based upon the American Association of State
Highways and Transportation Officials, An Information Guide for Roadway Lighting. The
survey respondents averaged 6.67 years for inspections; Municipalities averaged every 5 years
and Investor Owned Utilities averaged 7.5 years. The timetable is:
• Electrical Connections
• Fuses
• Grounding
• Security
The following is a timetable for inspection:
• Electrical Connections – Inspect when lamp is replaced
• Fuses - Inspect when lamp is replaced
• Grounding- Inspect when lamp is replaced
• Security- Inspect when lamp is replaced
Operations and Maintenance Checklist
Developing a proper operations and maintenance inspection checklist for street lighting
maintenance is very important to maintain adequate levels of reliability. The survey results and
industry research found the most common items checked in an operation and maintenance plan.
The following is a summary of checklist items:
• Lighting Controls
• Check/Replace Lamps
• Clean Refractors
• Check Luminaire Parts
• Check Pole
• Wiring
• Voltage
• Night Patrolling
• Troubleshooting
The following timetable for inspection is based upon the American Association of State
Highways and Transportation Officials, An Information Guide for Roadway Lighting. The
survey respondents averaged 6.67 years for inspections; Municipalities averaged every 5 years
and Investor Owned Utilities averaged 7.5 years. The timetable is:
• Lighting Controls – Inspect when lamp is replaced
• Check/ Replace Lamps – Replace based on replacement schedule
• Cleaning Refractors- Inspect when lamp is replaced
• Check/ Replace Luminaire Parts- Inspect when lamp is replaced
• Check/ Replace Pole- Inspect when lamp is replaced. Replace only when broken.
10
•
•
•
•
Wiring- Inspect when lamp is replaced. Replace only when broken.
Voltage- Inspect when lamp is replaced
Troubleshooting- On an as needed basis to determine problems
Night Patrolling- On an as needed basis to determine problems
Summary
The Street Lighting Best Practices report compiles the most common utility applications of street
lighting techniques in an effort to enlighten and inform. Every effort is made to explain the
purpose of each section, helping others avoid common mistakes and pitfalls. Special attention is
focused on touch potential, explaining the hazards associated with it and measures that can be
taken to help avoid it. Electric shock and how it affects a person is addressed as part of the touch
potential explanation.
Another integral part of the report focuses on the need to protect life and property. The use of
breakaway poles, to protect occupants of the vehicle from impact injury, and dead break wiring
to prevent the ignition of a fire or the inadvertent electrocution of vehicle occupants is crucial
with poles located in the clear zone. The proper pairing of light fixture to pole height is
paramount in developing uniformity in lighting conditions. The more uniform the light, the more
able the driver is to see obstructions or people on the roadside, possibly preventing a tragedy.
When a well designed and maintained system is in place, an increase in safety, security and
aesthetics is the result.
11
III.
ILLUMINATION LEVELS
A complete summary of the illumination guidelines for roadway lighting is provided at the end
of this section. For major, collector, and local roadways, the recommended illumination levels in
both the AASHTO “An Information Guide for Roadway Lighting” guide and in IESNA/ANSI
RP-8-00 “American National Standard Practice for Roadway Lighting” are equivalent.
However, this assumes that the three classifications that define the level of pedestrian conflict are
equivalent. While the alley is defined in IESNA RP-8-00, illumination levels are not given for
that roadway type, whereas they are given in the AASHTO guide. The AASHTO classifications
are the same as those used by utilities and include residential, intermediate, and commercial.
A study performed by the Kentucky Transportation Center includes the results of a survey of
states and the guidelines that they use to light their roadways. This study found that the
AASHTO and ANSI/IESNA RP-8-00 guides were used most often as guidelines to set
illumination levels.
It should be noted that both AASHTO and ANSI/IESNA documents include design
recommendations to limit the veiling luminance (glare) from roadway lighting applications. In
the tables included at the end of this section, recommendations for the veiling luminance ratio for
each roadway type are given.
Priorities for Street Lighting
Safety is not the only consideration when city or municipality representatives are making street
lighting decisions. Societal goals may include increasing safety and security, enhancing
economic development, highlighting historic areas or landmarks, and sending messages.
Pedestrian Conflict Areas
For the determination of appropriate illumination levels, each type of roadway has associated
pedestrian conflict classifications. Pedestrian conflict is related to the number of pedestrians that
walk along the roadway of interest. The AASHTO guide and IESNA RP-8-00 both define these
pedestrian conflict areas. AASHTO defines the level of pedestrian conflict using the terms
residential, intermediate, and commercial. IESNA/ANSI RP-8-00 uses the terms Low, Medium,
and High. These pedestrian conflict classifications are loosely synonymous. However, in
IESNA/ANSI RP-8-00, guidelines are provided to relate the number of pedestrians walking on
the street within a given time frame to a pedestrian conflict classification. For example, they
suggest that for a roadway with over 100 pedestrians walking on a street within the hours of
18:00 to 19:00, the pedestrian conflict is high.
Safety
While headlights on cars provide forward lighting for the driver, street lighting illuminates the
roadway showing the driver changes in direction up ahead, obstacles in the way, and the
roadway surface conditions. Street lighting lights more than just the road; walkways and
adjacent areas to the road also benefit. Pedestrians, cyclists, children playing in the front yard,
and other non-motorists are more readily seen with street lighting. In their recommended
practices, the IESNA (1999 and 2000) has recommendations for lighting that illuminates
12
intersections allowing oncoming drivers to see other vehicles, as well as pedestrians and cyclists.
Street lighting helps to mitigate headlight glare as well.
Security
While there is controversy about whether electric lighting improves security (Painter, 2001,
Boyce 1990, Tien 1979), there is no question that one feels safer walking or driving on well-lit
streets and in well-lit parking lots. Boyce (1990) found that an illuminance of 1-3 footcandles
provides the appearance of good security. Security may be thought of as freedom from worry in
regard to the security of people and property. The purpose of security lighting is to deter the
intruder, aid law-abiding citizens in recognizing danger, and to help law enforcement in the
identification process after a crime has occurred. An intruder may be deterred if the criminal is
easily seen at a distance allowing the victim time to prepare. Brightness of the neighborhood,
uniformity of the brightness of the area, and whether there is lighting outside of the area lit by
security lighting are three factors that influence deterrence. In order for security lighting to be
effective, minimum light levels that achieve the objectives of brightness and uniformity must be
met (Boyce 2000, Rombauts 1989, Boyce 1990).
Design of Roadway Lighting
Once the decision to light has been made, selecting an appropriate lighting fixture is in order. A
number of factors must be considered in the design of a lighting installation. These factors
include fixture style, height, placement, lamp type, brightness, color, life, and cost. Many of
these factors and a list of manufacturers that offer roadway luminaires is available in Specifier
Reports: Parking Lot and Area Luminaires (McColgan et al. 2004).
Efficient Technologies
There is no single best technology for street lighting, but there are relative benefits and
drawbacks of different types of lamps and luminaires. Mercury vapor lamps are found in many
older street lighting installations but these lamps are relatively inefficient and should not be used
in any new or retrofit installations. Almost all lamps used in street lighting require a ballast to
provide the proper voltage and current to the lamp; these will also use some energy and impact
the overall energy use. Finally, even the most efficient lamp and ballast can be made very
inefficient by using luminaires that trap light inside. A luminaire that emits less than half of the
light generated by the lamp and ballast should be avoided.
Appropriate Pole Heights
In different locations, different pole heights can be appropriate for the desired appearance and
required lighting. The "cobra head" type of luminaire seen on many streets and roadways is often
found on approximately 30 foot poles. Architectural or decorative types of luminaires might have
a scale that requires shorter pole heights. At the same time, the use of high-wattage, very
efficient light sources on lower poles could possibly lead to unwanted glare. These factors must
be balanced. When existing utility poles are used, careful attention to luminaire selection is
important so that it is suitable for the pole heights.
13
Appropriate Pole Spacing
The height of street lighting poles will impact how uniform the light levels are in the street and
surrounding area. At times, visibility can be reduced if lighter and darker areas have large
differences in light level. A well designed lighting installation will have sufficient uniformity.
This issue can be especially important in a retrofit installation where existing pole mounting
locations are going to be used with no additional pole mountings, or, as described above, when
existing utility poles are to be used. Changes in luminaire type and pole height can also impact
the uniformity.
Consequences of Roadway Lighting
The purpose of roadway lighting is to provide visibility to drivers at night. Increasing safety and
reducing the number of automobile crashes are typical goals when roadway lighting is being
considered. While the driving public demands roadway lighting, there are also negative aspects
to roadway lighting. Light pollution is an unwanted consequence of roadway lighting and
includes such effects as sky glow, light trespass, and glare.
Sky glow is the brightening of the sky due to outdoor lighting and is usually objected to because
it inhibits one’s ability to see and appreciate the stars.
Light trespass is light falling where it is not wanted or needed. Light from a streetlight or a
neighbor’s floodlight that illuminates your bedroom at night is an example.
Glare is excessive brightness causing discomfort or visual disability. Two examples that may
result in discomfort or disability glare include an unshielded luminaire where the lamp can be
directly seen or a misaimed vehicle headlight.
Concerns about light pollution and light trespass are growing. Many states and localities are
adopting lighting ordinances to limit the quantity of light used, the type of lighting fixtures used,
and the amount of light allowed onto adjacent properties.
The IESNA (2000) has developed a classification system for the distribution of light from
outdoor lighting luminaires. The cutoff classification system limits the amount of light emitted
directly above the horizontal and, in addition, limits the amount of light emitted between 80º and
90º from nadir. Angles referenced by the IESNA cutoff classifications are illustrated in Figure 1.
14
Figure 1 Angles referenced by the IESNA Cutoff Classifications
The two most stringent classifications are cutoff and full cutoff luminaires. Full cutoff luminaires
emit no light upward and tend to emit very little at angles near horizontal. Cutoff luminaires may
emit some light upward and also tend to emit little light near horizontal. The semi cutoff
classification is the least stringent and usually permits more light upward and at angles near the
horizontal. However, it is possible for a semi cutoff luminaire to generate no upward light, if it
exceeds certain limits for light near horizontal angles. This could lead to increased glare but
might be suitable for environments when vertical illumination is desired for recognition of
people or other vertically oriented objects.
Light trespass may be minimized by adding shields to luminaires to block light into unwanted
locations. A limit on light trespass is sometimes specified as a maximum vertical illuminance on
a window (ILE, 2000) or as the illuminance at the eye in a plane perpendicular to the line of site
(IESNA 1999).
Environmental zones are also used to limit light trespass and uplight (IESNA 1999, CIE 1997).
Environmental zones allow for different lighting requirements for different levels of population
and desire for darkness.
Recommendations
Pedestrian Conflict Areas
The pedestrian conflict areas of residential, intermediate, and commercial are consistent with the
definitions provided by AASHTO. These pedestrian conflict area definitions are used by many
states to define their roadways. This terminology is loosely synonymous with the terminology
used by IESNA. Consider the IES recommendation of monitoring the pedestrian traffic on
roadways that obviously fit into these pedestrian classifications. Associate the pedestrian traffic
value to each pedestrian conflict area to simplify the determination of future roads.
Illumination Levels and Roadway Classifications
The roadway classifications alley, local, collector, and major are consistent with the definitions
provided by AASHTO. These roadway classifications are used by many states to define their
roadways. This terminology is synonymous with the terminology used by IESNA.
15
Select illumination levels provided by AASHTO “Information Guide for Roadway Lighting”.
These illumination levels are the same as those in ANSI/IESNA RP-8-00. A majority of states
around the country also use these two documents as guidelines for illumination levels. The
current terminology used by some utilities matches the terminology used in the AASHTO
document.
Design of Roadway Lighting
Develop a street lighting design process that includes selecting appropriate luminaires, using
efficient lamp and ballast technologies, and selecting appropriate pole heights and spacing to
meet the desired lighting objectives.
Consequences of Roadway Lighting
When designing roadway lighting, minimize light pollution by:
•
Using the minimum light levels to meet the lighting objectives.
•
Using cutoff and full cutoff fixtures to minimize glare and uplight.
•
Considering the negative impact of the lighting on adjacent properties.
AASHTO’S GUIDELINES FOR “AVERAGE MAINTAINED ILLUMINANCE”
Average Maintained Horizontal Illuminance *
for Roadways Other Than Freeways, Walkways and Bicycle Lanes
R1
Roadway and
Walkway
Classification
Footcandles
Average Illuminance
Pavement Classification
R2&R3
R4
FootFootUniformity
Lux candles Lux candles Lux avg/min
Expressway**¹
Commercial
Intermediate
Residential
0.9
0.7
0.6
10
8
6
1.3
1.1
0.8
14
12
9
1.2
0.9
0.7
13
10
8
3:1
Major¹
Commercial
Intermediate
Residential
1.1
0.8
0.6
12
9
6
1.6
1.2
0.8
17
13
9
1.4
1
0.7
15
11
8
3:1
Collector¹
Commercial
Intermediate
Residential
0.7
0.6
0.4
8
6
4
1.1
0.8
0.6
12
9
6
0.9
0.7
0.5
10
8
5
4:1
Local¹
Commercial
Intermediate
Residential
0.6
0.5
0.3
6
5
3
0.8
0.7
0.4
9
7
4
0.7
0.6
0.4
8
6
4
6:1
Commercial
0.4
4
0.6
6
0.5
5
16
R1
Roadway and
Walkway
Classification
Alleys
Sidewalks
Footcandles
Average Illuminance
Pavement Classification
R2&R3
R4
FootFootUniformity
Lux candles Lux candles Lux avg/min
Intermediate
Residential
0.3
0.2
3
2
0.4
0.3
4
3
0.4
0.3
4
3
6:1
Commercial
Intermediate
Residential
0.9
0.6
0.3
10
6
3
1.3
0.8
0.4
14
9
4
1.2
0.7
0.4
13
8
4
3:1
4:1
6:1
1.4
15
2
22
1.8
19
3:1
Pedestrian Ways and
Bicycle Lanes²
*Average illuminance on the traveled way or on the pavement area between curb lines of curbed
roadways.
**Both mainline and ramps. Expressways with full control of access are covered in the section
on Freeways.
¹This assumes a separate facility. Facilities adjacent to a vehicular road should use the
illuminance or luminance levels for the roadway.
² Adapted from “American National Standard Practice for Roadway Lighting,” ANSI/IESNA
RP-8, 1983: Illuminating Engineering Society of North America. Used by Permission.
AASHTO’S GUIDELINES FOR “AVERAGE MAINTAINED LUMINANCE”
Average Maintained Luminance Design Values for Roadways Other than Freeways
Luminance
Veiling
Luminance
Uniformity
Ratio
foot(cd/m²) lamberts Lavg/Lmin Lmax/Lmin Lv (max)/Lavg
1.0
0.29
3:1
5:1
0.8
0.23
3:1
5:1
0.3:1
0.6
0.17
3.5:1
6:1
Lavg
Roadway
Classification
Expressway*
Commercial
Intermediate
Residential
Major*
Commercial
Intermediate
Residential
1.2
0.9
0.6
0.35
0.26
0.17
3:1
3:1
3.5:1
5:1
5:1
6:1
Commercial
0.8
0.23
3:1
5:1
17
0.3:1
Veiling
Luminance
Luminance
Uniformity
Ratio
footL
(cd/m²) lamberts Lavg/Lmin Lmax/Lmin
v (max)/Lavg
0.6
0.17
3.5:1
6:1
0.4:1
0.4
0.12
4:1
8:1
Lavg
Roadway
Classification
Collector*
Intermediate
Residential
Local*
Commercial
Intermediate
Residential
0.6
0.5
0.3
0.17
0.15
0.09
6:1
6:1
6:1
10:1
10:1
10:1
0.4:1
Alleys
Commercial
Intermediate
Residential
0.4
0.3
0.2
0.12
0.09
0.06
6:1
6:1
6:1
10:1
10:1
10:1
0.4:1
*Adapted form “American National Standard Practice for Roadway Lighting,” ANSI/IES RP-8,
1983: Illuminating Engineering Society of North America. Used by permission.
ANSI/IESNA’S GUIDELINES FOR “AVERAGE MAINTAINED ILLUMINANCE”
Illuminance Method – Recommended Values (RP-8)
Road and Pedestrian Conflict Area
Pavement Classification
Road
Pedestrian
R1
R2&R3
R4
Conflict Area
lux/fc
lux/fc
lux/fc
Freeway Class A
6.0/0.6
9.0/0.9
8.0/0.8
Freeway Class B
4.0/0.4
6.0/0.6
5.0/0.5
High
10.0/1.0
14.0/1.4
13.0/1.3
Expressway
Medium
8.0/0.8
12.0/1.2
10.0/1.0
Low
6.0/0.6
9.0/0.9
8.0/0.8
High
12.0/1.2
17.0/1.7
15.0/1.5
Major
Medium
9.0/0.9
13.0/1.3
11.0/1.1
Low
6.0/0.6
9.0/0.9
8.0/0.8
High
8.0/0.8
12.0/1.2
10.0/1.0
Collector
Medium
6.0/0.6
9.0/0.9
8.0/0.8
Low
4.0/0.4
6.0/0.6
5.0/0.5
High
6.0/0.6
9.0/0.9
8.0/0.8
Local
Medium
5.0/0.5
7.0/0.7
6.0/0.6
Low
3.0/0.3
4.0/0.4
4.0/0.4
18
Uniformity
Ratio
Eavg/Emin
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
4.0
4.0
4.0
6.0
6.0
6.0
Road and Pedestrian Conflict
Area
Road
Pedestrian
Conflict
Area
Freeway Class A
N/A
Freeway Class B
N/A
High
Expressway
Medium
Low
High
Major
Medium
Low
High
Collector
Medium
Low
High
Local
Medium
Low
Average
Luminance
Uniformity
Ratio
Uniformity
Ratio
Lavg
(cd/m²)
0.6
0.4
1.0
0.8
0.6
1.2
0.9
0.6
0.8
0.6
0.4
0.6
0.5
0.3
Lavg/Lmin
(maximum Allowed)
Lmax/Lmin
(maximum Allowed)
(maximum Allowed)
3.5
3.5
3.0
3.0
3.5
3.0
3.0
3.5
3.0
3.5
4.0
6.0
6.0
6.0
6.0
6.0
5.0
5.0
6.0
5.0
5.0
6.0
5.0
6.0
8.0
10.0
10.0
10.0
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.4
0.4
0.4
0.4
0.4
0.4
Veiling
Luminance
Ratio
Lvmax/Lavg
NCHRP’S GUIDELINES FOR “AVERAGE MAINTAINED ILLUMINANCE”
NCHRP Report 152 “Warrants for Highway Lighting”
Recommendations for Average Maintained Horizontal Illumination
Roadway Class
Foot-candles
Lux
Freeways, including major
0.6
6.0
interchanges
Primary arterials,
1.0
11.0
expressways, major highways
0.6
6.0
Secondary arterials, major
collectors, secondary
highways
Minor collectors, minor
0.4
4.0
commercial roads
Local roads, streets, alleys
0.2
2.0
19
AASHTO’S Classification of Roadways, Walkways, and Areas
Roadway and Walkway Classifications
(a) Freeway. A divided major highway with full control of access and with on crossing s at
grade.
(b) Expressway. A divided major arterial highway for through traffic with full or partial
control of access and generally with interchanges at major crossroads. Expressways for
non-commercial traffic within parks and park like areas are generally known s parkways.
(c) Major. The part of the roadway system that serves as the principal network for through
traffic flow. The routes connect areas of principal traffic generation important rural
highways entering the city.
(d) Collector. The distributor and collector roadways serving traffic between major and local
roadways. These are roadways used mainly for traffic movements within residential,
commercial and industrial areas.
(e) Local. Roadways used primarily for direct access to residential, commercial, industrial,
or other abutting property. They do not include roadways carrying through traffic. Ling
local roadways will generally be divided into short sections by collector roadway
systems.
(f) Alleys. A narrow public way within a block, generally used for vehicular access to the
rear of abutting property.
(g) Sidewalks. Paved or otherwise improved areas for pedestrian use, located within public
street rights of way which also contain roadways for vehicular traffic.
(h) Pedestrian ways. Public sidewalks for pedestrian traffic generally not within rights of
way for vehicular traffic roadways. Included are skywalks (pedestrian overpasses), subwalks (pedestrian tunnels), walkways giving access to park or block interiors and
crossing near centers of long blocks.
(i) Bicycle Lanes. Any facility that explicitly provides for bicycle travel.
Area Classifications
(a) Commercial. That portion of a municipality in a business development where ordinarily
there are large numbers of pedestrians and a heavy demand for parking space during
periods of peak traffic or a sustained high pedestrian volume and a continuously heavy
demand for off-street parking space during business hours. This definition applies to
densely developed business areas outside of, as well as those that are within, the central
part of a municipality.
(b) Intermediate. That portion of a municipality which is outside of a downtown area but
generally within the zone of influence of a business or industrial development, often
characterized by a moderately heavy nighttime pedestrian traffic and a somewhat lower
parking turnover than is found in a commercial area. This definition includes densely
developed apartment areas, hospitals, public libraries, and neighborhood recreational
centers.
(c) Residential. A residential development or a mixture of residential and commercial
establishments, characterized by few pedestrians and a low parking demand or turnover
at night. This definition includes areas with single family homes, townhouses, and/or
small apartments. Regional parks, cemeteries, and vacant lands are also included.
20
ANSI/IESNA’S Roadway, Pedestrian Walkway, and Bikeway Classifications
a) Freeway. A divided major roadway with full control of access (no crossings at grade).
This definition applies to toll as well as non-toll roads.
i.
Freeway A. Roadways with greater visual complexity and high traffic volumes.
Usually this type of freeway will be found in major metropolitan areas in or near
the central core and will operate through some of the early evening hours of
darkness at or near design capacity.
ii.
Freeway B. All other divided roadways with full control of access.
b) Expressway. A divided major roadway for through traffic, with partial control of access
and generally with interchanges at major crossroads. Expressways for noncommercial
traffic within parks and park-like areas are generally known as parkways.
c) Major. That part of the roadways system that serves as the principal network for throughtraffic flow. The routes connect areas of principal traffic generation and important rural
roadways leaving the city. These routes are often known as “arterials,” “thoroughfares,”
of “preferentials.” They are sometimes subdivided into primary and secondary; however,
such distinctions are not necessary in roadway lighting.
d) Collector: Roadways servicing traffic between major and local streets. These are streets
used mainly for traffic movements within residential, commercial and industrial areas.
They do not handle long, through trips. Collector streets may be used for truck or bus
movements and give direct service to abutting properties.
e) Local: Local streets are used primarily for direct access to residential, commercial,
industrial, or other abutting property. They make up a large percentage of the total street
system, but carry a small proportion of vehicular traffic.
f) Alley: narrow public ways within a block, generally used for vehicular access to the rear
of abutting properties.
g) Sidewalk: Paved or otherwise improved areas for pedestrian use, located within public
street rights-of-way, which also contain roadways for vehicular traffic.
h) Pedestrian Walkway: A public walk for pedestrian traffic, not necessarily within the
right-of-way for a vehicular traffic roadway. Included are skywalks (pedestrian
overpasses), subways (pedestrian tunnels), walkways giving access through parks or
block interiors, and mid-block street crossings.
i) Isolated Intersection: The general area where two or more non-continuously lighted
roadways join or cross at the same level. This are includes the roadway and roadside
facilities for traffic movement in that area. A special type is the channelized intersection,
in which traffic is directed into definite paths by islands with raised curbing,
21
j) Isolated Traffic Conflict Area: A traffic conflict area is an area on a road system where an
increased potential exists for collisions between vehicles, vehicles and pedestrians, and
vehicles and fixed objects. Examples include intersections, crosswalks and merge areas.
When this area occurs on a roadway without a fixed lighting system (or separated from
one by 20 seconds or more of driving time), it is considered an isolated traffic conflict
area.
k) Bikeway: Any road, street, path, or way that is specifically designated as being open to
bicycle travel, regardless of whether such facilities are designated for the exclusive use of
bicycle or are to be shared with other transportation modes. Five basic types of facilities
are used to accommodate bicyclists:
l) Shared lane: shared motor vehicle/bicycle use if a “standard”-width travel lane.
m) Wide outside lane: an outside travel lane with a width of at least 4.2 m (13.8ft.).
n) Bike lane: a portion of the roadway designated by stripping, signing, and/or pavement
markings for preferential or exclusive use of bicycles.
o) Shoulder: a paved portion of the roadway to the right of the edge stripe designed to serve
bicyclists.
p) Separate bike path: a facility physically separated from the roadway and intended for
bicycle use. (See IESNA DG-5-94, Lighting for Walkways and Class 1 Bikeways for
requirements in these areas.)
q) Median: The portion of a divided roadway physically separating the traveled ways for
traffic in opposite directions.
Pedestrian Conflict Area Classifications
The major, collector and local street classifications appropriately describe general conditions of
vehicular traffic conflict, which is responsible for a disproportionate number of nighttime
fatalities, is the vehicle/pedestrian interaction. The magnitude of pedestrian flow is nearly always
related to the abutting land use. Three classifications of pedestrian night activity levels and the
types of land use with which they are typically associated are given below:
High – Areas with significant numbers of pedestrians expected to be on the sidewalks or
crossing the streets during darkness. Examples are downtown retail areas, near theaters,
concert halls, stadiums, and transit terminals.
Medium – Areas where lesser numbers of pedestrians utilize the streets at night. Typical
are downtown office areas, blocks with libraries, apartments, neighborhood shopping,
industrial, older city areas, and streets with transit lines.
22
Low – Areas with very low volumes of night pedestrian usage. These can occur in any of
the cited roadway classifications but may be typified by suburban single family streets, very
low density residential developments, and rural or semi-rural areas.
The choice of the appropriate lighting level for a street is engineering decision. If needed, one
hour pedestrian counts can be taken during the average annual first hour of darkness (typically
18:00 to 19:00hours). A section of typical land use can be sampled by counting one or two
representative blocks, or a single block of unusual characteristics can be counted, perhaps at a
different hour, such as discharge from a major event. The volume of pedestrian activity during
the hour of count that warrants increased lighting levels is not fixed and represents a local option.
Guidelines for possible local consideration are:
Low – 10 or fewer
Medium – 11 to 100
High – over 100
These volumes represent the total number of pedestrians walking on both sides of the street plus
those crossing the street at non-intersection locations in a typical block or 200 meter (656 ft.)
section.
23
IV.
PROPER CODE SELECTION AND IMPLEMENTATION
Outdoor lights used to illuminate streets must be designed in compliance with the applicable
safety codes. The initial task is determining which code is appropriate for the individual street
lighting system. The selection of the appropriate code should be determined based on the type of
personnel who are operating the system.
There are two primary codes used in the United States; the National Electrical Code (NEC) and
the National Electrical Safety Code (NESC). However, California uses its own code for utilities,
California Public Utilities Commission General Order 95 and General Order 128. These General
Orders apply to those utilities under the jurisdiction of the Public Utilities Commission, State of
California.
The NEC is developed and maintained by the National Fire Protection Association with updates
every two years. This code can generically be described as applying to public and private
premises and the associated common areas (refer to Article 90.2(A)(2)).
The NESC is maintained by a committee of the Institute of Electrical and Electronics Engineers,
Inc. (IEEE) and is approved by the American National Standards Institute (ANSI). This code is
updated every 4 to 5 years with the next revision scheduled for 2007. This code generally
applies to electric and communication utilities (refer to Section 1 Rule 011.A). The transition
point from the NESC to NEC is referred to as the “service point” (refer to Section 1 Rule 011.B).
The major distinction between the two codes is the style of the codes. The NESC is a
performance-based code while the NEC is a prescriptive-based code. A performance base code
provides rules for how a system should perform, but does not provide details on how to achieve
this performance. An example is the NESC requires 12 kV conductors be 18.5 feet above
ground, but it does not say how this is to be achieved. The designer can use short poles with
short spans or tall poles and long spans but when the design is complete, it must provide 18.5
feet of clearance above ground.
The NEC, however, is a prescriptive-based code. This code does not list performance criteria;
rather the code says exactly how a system is to be designed. This achieves the safety objectives
contained in Article 90.1(A). An example is the very specific rules in sizing of protective
devices to achieve the safety objective of preventing overloaded system components. One
reason for a prescriptive-based code is that many jurisdictions have no inspections and others
have inspectors with no specialized electrical training. Another reason for a prescriptive-based
code is it does not require an advanced engineering degree to design a system. Rather, the
designer need only adhere to all of the NEC requirements.
This difference in the style of the codes leads to confusion when comparing design options for
street lighting systems. The NESC method leaves the design decisions to the engineer who is
responsible for complying with the performance standards. Whereas the NEC provides explicit
rules for the design, which if followed, achieve the NEC’s safety objectives.
24
This difference will be more apparent as the issue of grounding options is explored in more
depth.
Which Code Applies to Municipal Street Lights?
The NEC and NESC have been developed by separate organizations which have lead to
conflicting codes. In the last few updates of both codes, an effort has been made to coordinate
the requirements of the codes. Included in this coordination is the definition of the scope of the
codes.
Article 90.2(B)(5) states the NEC does not cover “installations under the exclusive control of an
electric utility where such installations are located in legally established easements, rights-ofway, or by agreement.” A complimentary set of rules is found in the NESC:
These rules are used to determine which code would apply to municipal street lights. It may be
necessary to expand on certain definitions to help identify the proper code. First, the NESC
defines a qualified person as an individual “having been trained in and having demonstrated
adequate knowledge of the installation, construction, or operation of lines and equipment and the
hazards involved, including identification of and exposure to electric supply lines and equipment
in or near the workplace” (refer to Part 1 Section 2, definitions, of the NESC). Typically, this
individual is thought of as a high voltage lineman or a first class lineman but when applied
exclusively to street lighting systems, which operate below 600 volts, it is appropriate to use
individuals trained only in these lower voltages.
The next definition to be considered is service point. This point is defined in both the NEC and
NESC as “the point of connection between the facilities of the serving utility and the premises
wiring”. (NEC Article 100, Definitions and NESC Section 2, Definitions). The point of
demarcation is generally defined by the serving utility who indicates where utility’s
responsibility ends. This point is not necessarily determined by who installed the conduit or
conductors but rather by which party has responsibility for operations, maintenance, and
replacement.
25
Another important definition to be considered is “utility” as used within the context of the
NESC. The NESC defines utility to mean “an organization responsible for the installation,
operation, or maintenance of electric supply or communications systems” (Part1 Section 2,
Definitions). Within this definition, a municipal water utility is not considered a utility by the
NESC.
The following case studies will help us apply the proper code, as defined above, to a given
situation. These cases are meant as a guide to help determine which codes govern the
installation.
Case Studies for Proper Application of Electrical Codes
Municipal Electric Utility Provides Street Lighting
When a municipality operates an electric utility and installs street lighting, the
appropriate code is the NESC. It must be recognized that the street lighting systems be in
the exclusive control of the electric utility. This means access to street light control
boxes must be limited, in addition to convenience outlets, which are often times included
on street light poles. If the public can access and use these outlets, the outlets are not in
the exclusive control of the utility. In this instance, the outlets must conform to the
requirements of the NEC which would require ground-fault circuit-interrupters on these
outdoor outlets (refer to NEC article 210.8) and a separate grounding conductor. If,
however, the convenience outlets are located high enough on the pole to limit public
access, the NESC would be the appropriate code (refer to NESC Rule 232B for
appropriate height requirements). The NESC provides no direction or rules regarding
outlets, but, the NEC is an excellent resource to determine appropriate measures to meet
the general performance requirements of the NESC as defined in Rule 011.
Electric Utility Provides Street Lighting
When an electric utility provides street lighting as a service to the municipality, the lights
will be governed by the NESC if the streetlights are in exclusive control of the utility.
The use of convenience outlets on these poles are commonly used for decorative displays
for Christmas and other holidays. The use of these outlets should be limited to the
electric utility or to individuals
deemed qualified by the electric
Qualified Person: Having been trained in and
utility. The NESC allows qualified having demonstrated adequate knowledge of
the installation, construction, or operation of
contractors to work on the electric
lines and equipment and the hazards involved,
utility’s system (NESC Section 1
including identification of and exposure to
Rule 011.C). Thus the electric
electric supply lines and equipment in or near
utility should be aware that
the workplace
providing permission to the
(NESC Part 1 Section 2, Definitions)
municipality’s personnel to access
these convenience outlets implies
that the utility believes the
municipality is utilizing
26
“qualified” persons. Alternately, the convenience outlets must be designed to meet the
requirements of the NEC if the utility does not recognize the municipal worker as a
qualified person.
Municipal Without an Electric Utility Installs Street Lights
In this scenario, a municipality receives power from an electric utility at utilization
voltage, then installs and maintains lights along its streets. For the NESC to be the
applicable code, the municipal must fit the definition of a utility. It may be difficult to
define that portion of the municipality that operates and maintains the street lights as a
utility. Often they are personnel who work for other municipal departments such as
water or parks and recreation. In most cases, if the municipality is not providing retail
electric service, the municipality should comply with the NEC. Under this scenario,
convenience outlets on the poles would also need to comply with the NEC. These
individuals must be trained as required by OSHA Subpart S of the General Industry
Standards to work on the electrical components of a street light system. It should be
noted that many municipal utilities are not required to comply with OSHA requirements.
Municipal Electric Utility Provides Street Lighting Outside of Their Service Territory
Some states have very distinct service territory lines between municipal electric systems
and other electric utilities. In these cases, as city limits expand, the service territory does
not expand. However, the city may want to provide street lighting on city streets outside
of their franchised service territory. In this case, the Municipal Electric Utility is
receiving power at utilization voltage from another electric utility and installing a street
lighting system. Because the Municipal Electric Utility fits the NESC’s definition of a
utility and assuming the Municipal Electric Utility is using qualified personnel, the
appropriate code for the street lighting system would be the NESC. This would even be
true if there is a meter at the point of service (which is not always the case). Just because
the Municipal Electric Utility receives energy at utilization voltage does not require the
street lighting system to comply with the NEC. Article 90.2(B)(5)(a) defines those
systems exempt from the NEC in the exclusive control of electric utilities that are located
in legally established easements, or rights-of-way. Any convenience plugs will be
governed by the NESC if the plugs are under the exclusive control of the utility (i.e. not
accessible to the general public).
OSHA Requirements
OSHA requires that person be trained in and familiar with the safety related work practices,
safety procedures, and other safety requirements that pertain to their respective job assignments.
OSHA standards in Subpart S of the General Industry Standards address electrical utilization
systems, i.e., installations of electric conductors and equipment which use electric energy for
mechanical, chemical, heating, lighting, or similar purposes. Subpart S protects most employees
from the hazards associated with electric utilization equipment and with premises wiring.
However, subpart S does not contain requirements protecting employees from the hazards arising
27
out of the operation or maintenance of electric power transmission or distribution systems. Thus
subpart S would apply to electricians working on premises wiring which would include area
lightning. Further, subpart S relates more to the electrical systems covered by the NEC since the
hazards are associated with utilization equipment.
OSHA along with the electric power industry and the International Brotherhood of Electrical
Workers (IBEW) developed 29 CFR 1910.269 which focuses on the operation and maintenance
of electric power transmission and distribution systems. 29 CFR 1926 Subpart V provides rules
for the construction of these systems.
A qualified person shall be trained and competent in all aspects of 29 CFR 1910.269(a)(2)(ii)
through (vii). OSHA also states only qualified persons may work on or with exposed energized
lines or parts of equipment operating at 50 volts or more (OSHA 1910.269(l)(1)). OSHA defines
a qualified person as one knowledgeable in the construction and operation of the electric power
generation, transmission, and distribution equipment involved, along with the associated hazards.
These work rules provide requirements for training when working with electrical systems but do
not directly address street lighting issues such as grounding practices.
OSHA 1910.269(l)(9) requires workers to treat non-current carrying metal parts as energized at
the highest voltage to which they are exposed unless the employer determines that these parts are
grounded before work begins. This rule can be important in the grounding methods used for
metal poles and fixtures. Some utilities provide a separate grounding conductor at the base of a
street light mast arm. This visible ground would provide confirmation of grounding. Other
utilities rely simply on the bonding of the neutral conductor inside the fixture for grounding of
the mast arm. This method would require the arm be treated as if it were energized with the
voltage inside the light fixture. Grounding of the base a metal pole or standard can be
accomplished is many difference ways. The method used can affect the work rules on how the
pole will be inspected.
Department of Transportation
Each state adopts its own requirements with regards to safety within the rights-of-way of their
state and county roads. These requirements are typically based on the recommendation
contained in the following documents;
ƒ “An Information Guide for Roadway Lighting, American Association of State
Highway and Transportation Officials (AASHTO)
ƒ “Report 152 – Warrants for Highway Lighting, National Cooperative Highway
Research Program (NCHRP)
ƒ “American National Standard Practice for Roadway Lighting (ANSI/IESNA RP8-00), Illuminating Engineering Society of North America in ANSI Practice for
Roadway Lighting ANSI RP-8)
The AASHTO standards, with regards to street lighting, focus mostly on the need to clear space
adjacent to the traveled edge of the roadway. There is a greater probability of a vehicle
contacting a pole when the pole is close to the traveled edge of a roadway. The AASHTO
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standards recognize that the speed of traffic is a component in determining this distance. The
problem faced by transportation engineers is that the poles must be close to economically light
the roadway. Without the lights the roadway is not as safe, but, with a pole near the edge of the
roadway, the roadway is not as safe. Thus a balance must be found between these conflicting
requirements.
In general, all ground mounted luminaire supports exposed to traffic and located within the clear
zone should be provided with breakaway or yielding bases, unless they are located with the
protection of a barrier (An Informational Guide for Roadway Lighting AASHTO 1984).
AASHTO Roadside Design Guide, 3-6 (2002) defines the clear zone based on vehicle speed,
average daily traffic, and shoulder slopes.
The AASHTO publication Standard Specifications for Structural Supports for Highway Signs,
Luminaries, and Traffic Signals, 2001 provide standards for breakaway poles. This document
states that breakaway supports shall be designed to yield, fracture or separate when struck by an
errant vehicle. Other sources of information on breakaway poles are Recommended Procedures
for Safety Performance Evaluation of Highway Features and AASHTO’s Roadside Design
Guide.
AASTHO recommends that efforts should be made in all breakaway poles that house electrical
components to effectively reduce fire and electrical hazards posed after structure impact. Upon
knockdown, the support should electrically disconnect as close to the pole base as possible.
Industry groups, such as the Illuminating Engineers Society of North America and AASHTO,
provide recommendations for lighting levels on roadways, provide sample lighting design
calculations, and set standards for fixtures and lens. However, they do not address the electrical
service or grounding requirements of the poles or light fixtures.
29
V.
WIRING AND CONSTRUCTION STANDARDS
The purpose of construction standards is to provide drawings and specifications that apply to
repetitive installations. This enables safety, reliability, operability, uniformity, appearance, and
economy to be coordinated in the system’s construction practices. This holds true for every
aspect of the transmission and distribution system, including street lighting. The task of
developing a street lighting best practices document required the review of many electric system
standards. The review of these standards ran the gamut from large investor owned utilities,
greater than 1 million customers, to Municipal systems with 100,000 customers. The following
will show the typical industry standard for each class of light found during our research.
The use of flood lights by utilities was typically 400 watt or 1000 watt high pressure sodium
fixtures. They were utilized when high intensity illumination of a specific non-roadway area was
needed. They are most commonly used for leased security lighting installations, such as parking
lots, business locations, apartment complexes, or transportation terminals. The most common
utilization voltages seen are 120 or 240 volts. Care must be observed in aiming and spacing the
floodlights. In order to maximize the useful light output, the floodlight should be aimed 2/3 of
the distance across the area to be lighted. Another rule of thumb to maximize the useful output is
to aim the light at a distance of 2 times the mounting height. Using the lower value of these two
methods is recommended. Other factors to avoid are directing the light into the face of
oncoming traffic as well as directing light trespass onto adjacent property. If tighter control of
lighting is required, consideration should be given to a visor. The spacing of floodlights is
important as well. Typical flood lights will give adequate lighting up to 45 degrees on either side
of the aiming line. If greater coverage is required, the use of two flood lights should be
considered. If two flood lights are utilized, overlapping is preferred to enhance light uniformity.
Wiring is typically run from a terminal block inside the fixture, out through a mast or arm, and
connected to an existing 120/240 volt line running along the pole line. The floodlight case is
bonded to the arm by means of attachment, and the arm is typically grounded to the system
neutral or ground wire lead.
Street lighting is of extreme importance in protecting the public from crime, pedestrians from
being struck, and motor vehicle accidents. These factors contribute to the need of uniform
lighting of roadways, bicycle travel lanes, and intersections. Utilities have a wide choice of
fixtures to accomplish these tasks. The fixtures utilized depend upon the task lighting
requirements and aesthetics. Some utilities define the types of street lighting by assigning
particular fixture wattage to categories of street lighting. One utility defines a 70 watt fixture as
an alley light, a 100 watt fixture as a local light, a 150 watt fixture as a collector light, and a 250
watt fixture as a major light. However, this is not typically the norm. Most utilities consider
anything 100 watts or below as a security light, and anything above as a street or area light.
Within these categories, several fixture types exist. The most common fixture used for a
roadway luminaire is a cobra head fixture. Typical sizes are 150 watt, 250 watt, and 400 watt.
The mounting heights and types vary; typically one can expect to see the cobra head fixture
mounted between 30 to 37 feet above the roadway. They may be mounted on wooden
distribution, aluminum, or fiberglass poles. Most utilities purchase and maintain a stock of high
pressure sodium vapor fixtures. Other utilities currently using mercury vapor fixtures are
30
planning to convert to the more efficient and cost effective high pressure sodium vapor fixture.
These fixtures are typically available as drop prismatic refractor glass, flat glass, short semicutoff, medium semi- cutoff, medium cutoff, and full cutoff. A recent push by an organization to
reduce light trespass into the night skies, Dark Skies, has seen the increased usage of medium
and full cutoff units. As indicated in the survey, most are currently utilizing a fixture of this
nature and the remaining utilities are heading in this direction.
Other fixtures which are utilized, but not as prevalent, are high mast and teardrop fixtures. These
have a more specialized application in roadway lighting. The high mast luminaire is ideal for
use on interstate highways or large areas requiring maximum pole spacing. The teardrop fixture
is used for a more 1930’s nostalgic look, providing a style of yesteryear while also being energy
efficient. Decorative fixtures are utilized for street lighting as well, however they are typically
confined to downtown areas or housing subdivisions. A typical style decorative light employed
by utilities is the Acorn fixture. It compliments parks, downtown, and residential roadways as
well as having excellent photometric capabilities and the lowest cost of most decorative fixtures.
These are all reasons why it is popular with utilities. The security light, or alley and local light
as referred to by some utilities, comes complete and ready for mounting in areas such as
barnyards, service drives, storage facilities, and roadways with light traffic. These are normally
rented to homeowners by the utility for lighting their yards and drives for safety and security
considerations. These are often referred to as bug lights. Almost all of the utilities operate these
fixtures at 120 or 240 volts. The standards for these typically address the height of the fixture on
the pole, the grounding of brackets or metallic poles, clearances from primary lines, and
protection details. In areas of high probability of vehicle to pole contact, some utilities opt for
breakaway pole options. There are many wiring options available for street and security lighting.
Street lighting can be accomplished utilizing existing wood distribution poles or aluminum poles
dedicated to lighting. The distribution pole wiring is typically run from a terminal strip inside
the cobra head fixture, through a mast or arm, and connected to a 120/240 volt line running along
the pole line. The head is bonded to the arm which in turn is grounded to the system neutral or
ground wire lead. In a case where an aluminum pole is utilized for support of the fixture, most
utilities attach a ground conductor from the pole and bond to the neutral run with the feed wire or
to a separate ground rod.
The review process compared a variety of standards from many utilities to that of the City of
Columbus, Ohio standards. It was found that the City of Columbus, Ohio standards were equal
to or exceeded the standards of the other utilities reviewed. The major difference was the
inclusion of specifications by the City of Columbus, Ohio for 480 volt lighting, which were not
found in the other utilities standards which were reviewed.
NESC Grounding Requirements
Grounding is a means used to provide safety to electrical workers and any people that may come
into contact with structures such as street light mast arms, metal poles and guy wires. The NESC
provides rules on grounding of components as a means to safeguard any person from injury that
could be caused by electrical potential. The rules on grounding can be found in Section 9,
Grounding Methods for Electric Supply and Communication Facilities, of the NESC 2002
edition. There two purposes for protective grounding;
31
1. Enhanced operation of system overcurrent protective devices
2. Minimize exposure of personnel to electrical potential
Clearing a fault quickly reduce the exposure of the person to the hazard. A low impedance path
to the source is required for overcurrent protective devices, to distinguish between load current
and fault current.
In Rules 215C1 and 314B, the NESC requires that certain metal supporting structures, including
lamp posts, be effectively grounded. It should be noted that these rules do not apply as long as
the voltage is less than 300 volts. However, when the voltage does exceed 300 volts, to comply
with this performance requirement it is necessary to understand the definition of “effectively
grounded.” In Section 2 of the NESC, the definition of effectively grounded is given as
“intentionally connected to earth through a ground connection or connections of sufficiently low
impedance and having sufficient current-carrying capacity to limit the buildup of voltages to
levels below that which may result in undue hazard to persons or to connected equipment”1.
There are two parts to this requirement.
1) Adequate current-carrying capacity
2) Sufficiently low impedance to prevent the buildup of hazardous voltages
Adequate current-carrying capacity refers to the conductor or conducting path used for
grounding the structure. If a grounding conductor is to be used, it must meet the requirements of
Rule 093. Simply stated the grounding conductor must have the ampacity of the phase conductor
that would supply the ground fault current or the maximum current that can flow though the
grounding conductor2. The grounding conductors are typically #8 AWG as a minimum. A #6 or
#4 AWG are also commonly used. Table 250.66 of the NEC provides some guidance on the
selection of grounding conductors for secondary circuits. Another method allowed by the NESC
for selecting the ampacity of a single grounding conductor connected to an electrode (driven
ground rod) is to divide the supply voltage by the resistance of the electrode. The metal structure
of the street light pole is allowed to be a part of the grounding path3. Thus the grounding
conductor can be attached at the base of the metal pole and does not need to run all the way up to
the street light fixture.
The other requirement is sufficiently low impedance to limit the buildup of voltages below levels
which may be hazardous. There are three possible methods to achieve the low impedance
requirement. One is to use the secondary circuit grounded conductor (the system neutral) to
bond to the metal structure or case. The other is to bond to a made electrode. The third is a
combination of the neutral and the made electrode.
1
Institute of Electrical and Electronic Engineers, Inc., Seventh Interim Collection of the National Electrical Safety
Code Interpretations, 1996-1997. New York, 1997, page 7.
2
Institute of Electrical and Electronic Engineers, Inc., National Electrical Safety Code, 2002 Edition, 093C8. New
York, 2002, page 20.
3
Institute of Electrical and Electronic Engineers, Inc., National Electrical Safety Code, 2002 Edition, 093A. New
York, 2002, page 18.
32
Use of System Neutral to Effectively Ground Street Light Poles and Mast Arms
The grounded circuit conductor (neutral) is used to ground a metal street light pole or mast arm.
This would be very similar to the situation described in Electric Shock and The Human Being,
Appendix C, Figure 7. During normal operation, the current flow in the neutral will cause a
voltage drop and therefore a potential difference may appear at the metal pole. This voltage rise
will be less than 4 volts and not perceptible to humans.
Figure 2 shows touch potential concerns when the neutral conductor is used for ground.If there is
a short between the hot leg and the metal pole, there are two paths for the fault current back to its
source. One path is through the system neutral conductor. The other path is through the
individual’s hand, out his feet and through the earth. The current division is based on the ratio of
resistances of the two paths.
Figure 2 Touch Potential Concerns
The path to ground may not always involve contact through an individuals hand and out his foot.
An incident occurred, resulting in a fatality, where a young boy contacted a street light pole and
fabric fence with his back and chest. This was a result of the boy trying to squeeze by the pole
and fence. The resistance with this type contact may be less than a hand entry and foot exit,
especially if wearing rubber sole footgear. Another possible entry exit point is an individual’s
back to his leg. This may occur if a person leans against a street light pole while sitting on a
guardrail, a likely scenario for a person resting while changing a tire on a motor vehicle. Many
contact and exit points exist having different resistance values. These need to be considered
when determining if a pole is effectively grounded. Figure 3 shows touch potential concerns
with a fabric fence within six feet of the utility pole.
If the system neutral impedance, from the pole back to the source, is much less than the
resistance of the body and the ground resistance at the person’s feet or other contact point, then
the pole would be effectively grounded. During a system fault, the return current will travel in
33
the system neutral and will have a voltage drop resulting in a potential at the pole when
referenced to remote earth or even to earth three feet away from the pole.
Figure 3 Touch Potential Concerns Hand to Hand Contact
In addition, unlike household wiring, there is normally no other grounded object within reach of
a utility pole which is one of the reasons why NESC does not utilize a safety ground and the
NEC does. However, NESC Rule 350F alludes to bonding all above ground metallic equipment
that is separated by less than 6 feet. While bonding does reduce the potential difference for
metal-to-metal touch potential, other issues may arise from this practice. Using Figure 4,
Bonding of Streetlight Pole to a Fence, as an example, the illustration shows the bond creates an
equipotential ground plane along the fence until the discontinuity of the fence at the gate. The
gate on one side will be on the same ground plane as the street light; however, the other side may
not be at the same potential, thus possibly creating a touch potential issue. Upon closer
inspection, each fence post will act as a ground rod and provide an alternate path back to the
source. Is the ground path sufficient enough to avert a touch potential incident? All variables
cannot be accounted for to definitively say yes. If the ground resistance of the post, acting as a
ground rod, is less than the resistance of the person coming into contact with the differing ground
planes, then the person may have averted a possible touch potential incident. Now consider the
following scenarios. A speed limit sign is six feet from a street light pole. The proximity of the
sign to the pole lends itself to being able to be reached by the average adult person. In an effort
to protect people, the speed limit sign is bonded to the pole to create an equipotential ground
plane. Now, within six feet of the speed limit sign is a school zone sign, should the school zone
sign be bonded to the speed limit sign? A difference in potential may exist because the ground
plane was extended from the street light pole to the speed limit sign possibly increasing the
occurrence of a touch potential situation. Consider further a bus stop sign six feet from the
school zone sign? Should bonding of the object occur for the same reason as before? Where
does this lead? Should bonding be performed at all? Should the gate have a jumper connection
to provide continuity and be afforded the protection of bonding? How far should the daisy chain
34
continue? These are all valid questions, but one must look at what is trying to be accomplished
by the bonding of the objects, which is, to effectively ground the equipment and reduce the
occurrence of a touch potential incident. Each of these objects is another ground point, acting
like a ground rod. When you parallel ground rods, you have an effect of lowering the resistance
at each point. If the resistance, at the point of the ground, is less than the resistance of the
person, the probable flow of objectionable current will be through the ground back to the source.
As a possible means to improve site safety, bonding of objects within six feet of a streetlight
pole, the average reach of an adult, will typically afford more protection for a touch potential
incident than just a ground rod located locally would. One may consider the use of bonding as a
prudent step in an attempt to protect the public.
Figure 4 Bonding of Street Light Pole to a Fence
The low impedance of the neutral will assure that the overcurrent protection will clear any faults.
Also, the voltage rise relative to the earth will be a function of the fault current and the resistance
of the neutral conductor or neutral network. If the item to be grounded is a metallic mast arm,
the height of the mast arm provides space separation from the public. In this case, workers are
required by Rule 441 to de-energize equipment operating above 300 volts, or use appropriate
protective equipment such as gloves. For lower voltages, there is no requirement for protective
equipment. In order to be hazardous to that employee, a short inside the lamp would have to
occur while the worker was in contact with the arm and another grounded component.
Using the system neutral as a grounding conductor on a metal street light pole is similar to
Appendix C, Figure 7. This implies that all of the metal street light poles must have a sufficient
grounding system to limit touch potential voltages to below a lethal level. However, as a
performance based code, the NESC Rule 215C1 states that on overhead supplied “metal or
metal-reinforced supporting structures, including lamps posts, metal conduits, hangers of
equipment...and operating handles shall be effectively grounded.” There is an exception to this
rule that exempts this grounding requirement for metal conduits, frames, and hangers if these
components are not exposed to voltages over 300 volts. This exception does not apply to the
metal supporting structure. Rule 314B requires that all underground cables supplying conductive
lighting poles shall be effectively ground.
Street Lighting Utilization Voltages
One of the more important decisions to make in the street lighting design process is determining
the voltage level at which you will operate your system. A lower operating voltage will result in
a greater current and fewer lights operating on your circuit. The opposite is also true, a higher
voltage will allow for a lower current and more lights on the circuit. Electrical energy losses are
reduced at higher voltages, however, past 300 volts, rules from the National Electrical Safety
Code (NESC) begin to apply. In order to operate efficiently, one must strike the proper balance
35
of voltage levels, acceptable electrical losses, and the amount of regulation you must contend
with. The Lighting Research Center of Rensselaer Polytechnic Institute (LRC) survey,
performed for this report, shows a majority of utilities utilize a 120 volt street lighting system
(62%) followed by a 240 volt street lighting system (28%). Street lighting system voltages of
480 volts (7%) and 277 volts (3%) are less frequently used.
Cooperative utilities are more likely to utilize the 120 volt street lighting system (70%) closely
followed by investor owned utilities (65%). Municipalities owning and operating street lighting
systems use 120 volt street lighting systems 59% of the time and municipal electric utilities 56%.
The survey found municipal electric utilities utilize the 240 volt street lighting system more than
other utilities, with 42% of the systems reporting this utilization voltage. Municipally owned
systems account for 36% of the utilization of the 240 volt street lighting system and investor
owned utilities account for 22%, Cooperative utilities rarely utilize this voltage level. A 277 volt
street lighting system appears to be extremely rare, with the only respondents utilizing this
voltage being cooperative utilities. The 480 volt street lighting system is also not often used by
the survey respondents (7%). Investor owned utilities are the most frequent users of the 480 volt
street lighting system, followed by municipally owned street lighting systems.
A need for additional wires may explain why only a small number of survey respondents are
utilizing the 480 volt street lighting system. This becomes an issue when pole space is at a
premium. Utilities governed by the NESC must maintain a vertical spacing of at least 6”
between conductors of differing voltages on any structure. This requirement can be found in
NESC Table 235-6. Most utilities distribution practices include stringing 120/240 volt service
wire along the roadways to service customers. Rather than running a second set of wires, and
using a different voltage, utilities will generally tap the existing 120/240 volt service wire for the
street lighting instead. Another factor is the cost differential between the common 120/240 volt
and 480 volt transformers.
Another reason that 120/240 volt service is selected over 480 volt service is the increased
likelihood of electrocution if a person comes in direct contact with the wire. Typical skin
resistance permits a current flow of approximately 0.024 to 0.080 amperes if a person touches a
120 volt conductor. This may be enough to cause fibrillation given sufficient time. However,
the current flow would be 0.096 to 0.320 amps if a person touches a 480 volt conductor, resulting
in a much higher likelihood of fibrillation (see Appendix C for more information on electrical
shock and the body).
One final consideration is the additional code compliance requirements. Those utilities governed
by the NESC will need to comply with performance based rules 215C1 and 314B. These require
that certain metal supporting structures, including lamp posts, must be effectively grounded.
These rules apply only to street lighting systems greater than 300 volts. Utilities operating at 480
volts would thus be required to comply with these extra performance based rules.
Based upon the survey results, common utility practices indicate the use of either a 120 or 240
volt service for street lighting as a best practice.
36
VI.
METHODS OF CONTROL OF STREET LIGHTING CIRCUITS
Utilities have many control methods for street lighting. These methods range from the average
electric photocell to advanced functions such as SCADA controlled dimming. The following is a
brief overview and introduction of technologies available in street lighting control.
Photocells
Photocells have and continue to be the most common method of street and floodlight control in
the electric utility industry. Based on a survey conducted for this document by the LRC,
photocells are utilized in 82% of lighting installations. The survey results are contained within
Appendix A of this document. Their low cost and high reliability make photocells a formidable
opponent. Photocells have changed throughout the years with increasing efficiency and better on
–off control. The principle of operation, for a conventional control, is not very complex. It
consists of a cell that is in series with a resistor which is mated to a strip of metal with certain
characteristics. During the day, light shines on the cell and it conducts. This lets the line voltage
through to the resistor. The resistor heats causing the metal mated to it to deflect. This
deflection opens a set of contacts which turns the light off. In the evening, limited light shines
and the cell does not conduct. The resistor does not heat and the metal does not deflect. At this
point the contact closes and the light is energized. The principle of operation for an electronic
control is more complex. The incoming line voltage is converted to direct current and sent to an
electronic circuit. The signal is taken from an analog state to a digital state, which is either an on
or off signal. The signal then initiates a coil with either full voltage or no voltage. This
conversion process removes the contact chatter associated with a slow break. Photocells can be
used in conjunction with external relays to energize multiple lights at the same time, often called
a master control. This is accomplished utilizing a circuit dedicated to street lighting. The line is
energized only when the photocell actuates the relay. According to the survey, only 17% of
respondents utilize this means of control. Utilities tend to use photocells more frequently (83%
for Municipal Utilities and 87% for Investor Owned Utilities) than municipally owned street
lighting (68%). The use of master controllers for street lighting is mainly used by municipalities
that own street lighting systems and accounts for a much smaller portion of the overall control of
street lighting (17%). The following is a quick review of advantages and disadvantages of
conventional and electronic controls:
Thermal Controls4
• Initial cost is low.
• Calibration tolerances are too wide causing large on/off ratios.
• Delayed turn off wastes energy in mornings.
• Poor quality (very short life leading to frequent replacements)
• Infrequently utilized by utilities.
AC Relay Controls5
4
American Electric Lighting Photo Control Guide
5
American Electric Lighting Photo Control Guide
37
•
•
•
•
•
•
Instant turn on-off.
Contact chatter prior to breaking load.
Initial cost is low.
Previously the most common type used by Utilities.
Delayed turn off wastes energy in mornings.
A lightning flash can cause the lamp to go off. Cool down and re-strike may take
several minutes.
Electronic Control with Thermal Switch4
• Effectively filters out short on or off cycles.
• The 30 to 60 second time delay for on/off is considered excessive.
• The on/off ratio can be 1:1.
Electronic Control with DC Relays4
• Instantaneous switching with no chatter or buzz.
• Small ratio will not cause excessive morning burning time.
• Large enough ratio to give positive switching with fast moving clouds.
• The control can be adapted to be blind to lightning or poorly aimed car headlights.
• Most common use control with utilities.
Monitoring and Control Systems
Monitoring and control systems available to electric utilities offer a great amount of flexibility in
the control and maintenance of the light, as well as the reduction of power consumption and
costs. These systems operate on many different software platforms and communications options.
They can be integrated into a Utilities SCADA or GIS system allowing a spatial representation
of street lights on system maps.
These systems offer the ability to control street lights on an individual or group basis, as well as
an entire urban area. The energy consumed when dimming or shutting off lights is then reduced.
This can be accomplished through automated measures or light intensity measurements. Control
can be accomplished manually, by internet, or cell phone, or a fixed time program. The
monitoring aspect allows the utility to obtain maintenance efficiencies resulting in a decrease in
operating expenses, reduction of calls related to lamp faults or failures, and data collection with
reporting capabilities.
The system can also be utilized to reduce light trespass. Organizations, such as the International
Dark-Sky Association (IDA) and other grass roots organizations have pushed government
entities to pass legislation for a reduction in light trespass. These systems can help supplement
other programs working to reduce light emissions and come closer to meeting the objectives of
IDA. A majority of respondents to the survey (54%) indicated that they utilize a full cutoff
fixture to meet the demands of groups like IDA while the remainder is looking at requiring full
cutoff lighting in the future.
38
A concern of Utilities and Public Safety officials is the failure of the central unit or
communications media. A system communications or processor failure does not mean
illumination will not occur. Most systems have a fail safe built in so that each light will fall back
to an internal program and continue to illuminate the street.
As technology advances and economies of scale are achieved, these systems will become
prevalent in the industry. Control, maintenance, and data acquisition from these systems will
fuel higher demand.
39
VII. OPERATION AND MAINTENANCE PLAN – Practices Determined
From Survey Conducted by LRC
A survey of street lighting practices was prepared by the LRC and handed out to participants in
the 2004 Street and Area Lighting Conference. Based on the responses of the survey
respondents, best practices for operation and maintenance were developed.
Nearly half of the survey respondents (48%) report that maintenance of streetlights is performed
by dedicated streetlight crews. Contractors perform this function 26% of the time and 26% of
the time it is performed by regular line crews. The use of high voltage linemen to perform
streetlight maintenance was reported by 50% of respondents. However, municipalities that own
streetlights are more likely to use low voltage line personnel.
Group relamping is only used by 38% of the respondents. All survey respondents indicated that
streetlight fixtures, poles and wiring are only replaced upon failure.
Inventories of streetlights in use are conducted by 71% of the survey respondents either as part of
any group relamping or conducted as separate inventories. Streetlight outage reporting is
predominately provided by customers (55%) and by police and a dedicated person within the
streetlight owning entity (21% each).
The annual maintenance cost per streetlight as reported in the survey varies greatly from a low of
$10 to a high of $400. The most likely costs for entities not conducting group relamping is
approximately $40.
Dedicated streetlight maintenance crews may be warranted if sufficient streetlights are owned by
a single entity.
Streetlight Poles
All survey respondents indicated they only replace streetlight poles upon failure. This practice is
recommended. Inspection of any wood streetlight only poles should occur at the same inspection
interval as wood overhead line poles. In fact, the inspection of wood streetlight poles should
occur at the same time as the line poles in the area are being inspected. This will eliminate
separate inspection trips for just the streetlight poles.
Dedicated Streetlight Wiring
The vast majority of survey respondents (79%) indicated they do not perform any streetlight
wiring inspections. Streetlight wiring is only replaced upon failure according to all survey
respondents. Replacement of only failed streetlight wiring is the recommendation set forth here.
However, there is an exception to this recommendation. Certain types of underground/direct
buried electrical wires are known to deteriorate more rapidly than their original specifications. If
these types of wires begin to have multiple failures throughout the streetlight system, it might be
less costly to replace all of this type of streetlight wire under a designed replacement plan rather
40
than wait for failures to occur. In order to determine these types of failures, a database must be
maintained. The use of databases will be addressed in further detail later in this document.
Inspection of streetlight wiring for safety purposes is discussed elsewhere. However, there is one
inspection that is recommended at the time of group relamping of underground fed streetlights.
If the streetlight wires are terminated at the base of the streetlight pole within a wiring hand hole
in the pole, inspections to ensure the cover for these hand holes is present and properly installed
should be conducted.
Streetlight Fixture Maintenance and Repair
All survey respondents indicated they only replace streetlight fixtures upon failure of the fixture.
It is believed this is a sound economic and safety policy. Therefore, it is recommended that
streetlight fixtures only be replaced upon their failure.
Low Capital Cost Streetlight Fixtures (cobra heads)
What is deemed a fixture failure for low cost streetlight fixtures? The recommended definition
of failure for these fixtures is anything that fails beyond lamps, photocells and the glass globe.
Replacing/repairing ballasts and other electrical components may cost (parts and labor) more
than replacing a low cost fixture.
High Capital Cost Streetlight Fixtures (decorative post tops, etc.)
All efforts should be made to repair the higher cost streetlight fixtures. Replacement of ballasts,
lenses, glass, photocells, etc. will be less costly than replacing the entire fixture. The higher cost
fixtures should be chosen with maintenance in mind. Easy to maintain fixtures that have snap in
connections for ballasts, photocells and other electrical components will reduce maintenance
costs.
Recommendations
Based on the results of the survey, it is not perfectly clear that group relamping is a best practice
for street lighting maintenance; however; it appears that larger utilities with a greater quantity of
lights would benefit more from a group relamping methodology. Smaller utilities with fewer
lights to maintain and patrol would probably realize that group relamping is too costly and
therefore spot relamping combined with night patrolling for burned out lamps would be more
economical. It is recommended that larger utilities establish a more pro-active street light
maintenance and repair program. This program would include a replacement rotation schedule
based on the following replacement criteria: type of light, area installed, age of lamp, and useful
life of lamp (utilizing life cycle curves provided by manufacturers).
The results of the survey showed that 71% of the respondents took inventory of their street
lighting systems either through relamping or a separate inventory. This step is essential in order
to determine which types of lights are present on the system, their classifications, and most
importantly their physical location. A GIS based mapping system would be ideal for developing
a street lighting maintenance plan.
41
A representative sample of one utilities’ methodology for categorizing the types of street lighting
are broken down below. They are separated into 4 categories based on wattages of the fixtures
and their locations:
Alley – 70 watts
Local – 100 watts
Collector – 150 watts
Major – 250 watts
Within these major lighting categories there are many types of fixtures including flood lighting,
street lighting, security lighting, and decorative lighting. It will be important to note the specific
fixture types at each location will need to be incorporated into the GIS mapping system in order
to prepare the operations and maintenance crews and allow for proper stocking of the repair
trucks. A GIS system is also a very valuable tool that can be used to track the in service dates of
street lighting equipment. By using these in service dates and comparing the hours in service for
lamps in the field to manufacturers life cycle curves, a more pro-active approach for lamp
replacement can be formulated. In addition, early failures of lamps could be noted and new life
cycle curves for lamps could be prepared.
Spot Relamping versus Group Relamping
Spot Relamping is defined as fixing lighting lamps only when they are broken. This program is
usually dependent on drive by inspections at night or consumer/police outage reports. Group
Relamping is defined as replacing lamps on a periodic replacement schedule or “best time
schedule”. A group relamping program is usually defined by area within a system and is largely
influenced by the luminaire life curves provided by lamp manufacturers. A “best time schedule”
is based on when the total cost of energy use, cost of installation, and relamping is at its
minimum. Effectiveness less than 50% is a good indicator while 33% to 25% of lamp life
remaining offers a good mix as well.6
The most debated issue surrounding lamp replacement is whether to do group relamping or to
replace lamps only upon notification of failure, i.e. spot relamping. Survey respondents
indicated a strong preference for spot relamping. Municipally owned utilities had even a
stronger preference for spot relamping.
The survey not withstanding, it is recommended that group relamping be pursued. All economic
studies on this subject show potential savings by using group relamping. The Illuminating
Engineering Society of North America (IESNA) design guide DG-4-03, Design Guide for
Roadway Lighting Maintenance, illustrates an analysis of spot versus group relamping. A
review of their assumed costs shows them to be reasonable. The use of the non-cycling,
environmentally friendly HPS lamp will further improve the economics of group relamping
because of the extended life of these lamps. The group relamping schedule can be stretched
from four years to five years.
6
Design Guide for Roadway Lighting Maintenance (DG-4-03) by IESNA Roadway Lighting Committee
42
Group relamping offers the appeal of more evenly aged lamps, while spot relamping can limit
light depreciation which is important for overall safety and security. While a spot relamping
program requires little planning to implement, a group relamping program requires considerable
planning to develop the schedules and personnel requirements for a cleaning or group relamping
program. Spot relamping is generally more expensive due to the increased labor costs involved
with the increased travel times that are incurred by replacing lamps across a wide service
territory. In addition, by relying on consumer or police outage reports, a utility employing a spot
relamping program may incur some liability with burned out lamps.
An example of the costliness of liability surrounding the maintenance of street lights happened to
a Florida utility. A civil case in Florida pitted the family of a man killed by a delivery truck
against a Florida utility. In this particular case, a young man was walking along a road during
the early morning hours and was struck and killed by a passing delivery truck. The family of the
deceased claimed that the street light near the accident, of which the utility owned and was
responsible for maintenance, was burned out. Since the light was burned out, the truck driver
could not see the man, and therefore the blame rested on the utility. The case went through
several courts and was ultimately decided for the Plaintiff. The utility had to write a check to the
family and agree to better maintenance procedures. By adopting a group relamping program, a
utility is better shielded from this type of litigation due to better service records and by being
able to prove that maintenance of street lights is performed in a timely manner.
Many states define an allowable percentage street lights out at a given time or have
recommendations for making repairs after outage calls. Connecticut and Massachusetts utilities
are required to re-lamp fixtures within 72 hours of notice of a problem. California requires a
specific maintenance schedule. The Institute Of Lighting Engineers (United Kingdom)
recommends that no more than 2% of public lighting should be out on any one night.
The City of Philadelphia has three different parties involved with their street lighting
maintenance, including the city street lighting shop, PECO Energy7, and a contractor. The
contractor works at night and is responsible for lamps and photocontrols. The contractor is also
required to perform weekly streetlight inspections. They report on problems and fix minor
problems such as a lamp replacement or a photocell. Otherwise, they submit a work order for
the city or PECO Energy to handle. The city shop is responsible for poles and luminaires.
PECO Energy is responsible for electrical distribution and taps. The contractor is allowed no
backlog. The city shop is allowed a backlog of 10 days on average for major repairs. PECO
Energy is allowed a backlog of 20 days on average for underground circuit repairs
Some of the benefits of a group relamping and maintenance plan for street lighting are as
follows:
•
Maintaining high standards of light output
7
Based on a presentation by Joseph Dyle, chief street lighting engineer for the city of Philadelphia , at the 2003
IESNA Street and Area Lighting Conference.
43
•
Minimizing the higher costs associated with random lamp failure replacement
•
•
Confining maintenance work to pre-planned areas
Preventing the expensive replacement of lighting control failure caused by
burning the lamp to destruction
•
Keeping energy usage to a minimum
Several studies have been performed by utilities to determine whether they should pursue a
group relamping program or continue their current program of spot relamping. The results of
these studies show that the total cost of maintaining a group relamping program can be more cost
affective than a spot relamping program. Some of the utilities who have had success with group
relamping include Madison Electric and Gas (MGE) and Upper Peninsula Power Company
(UPPCO). Each utility is different in terms of consumers, equipment used, cost of labor, and
capabilities. Utilities are urged to do a cost analysis to determine whether or not a group
relamping program is right for them. The IESNA Design Guide for Roadway Lighting
Maintenance (DG-4-03) is an excellent source for an example of maintenance practices and for
guidance in performing a cost benefit analysis.
An economic analysis of group relamping for a large municipal utility using the methodology
depicted in Table 1 of IESNA DG-4-03 follows. It assumes the utility has 90,000 streetlights in
place. It also assumes the use of the non-cycling HPS lamps. Cost of these lamps are
approximately $11.50, the group relamping cycle is five years, group relamping costs are $12 per
streetlight and spot relamping costs are $100 per streetlight. These costs include travel time,
time to setup, replace the lamp and clean the fixture.
Item Description
1. Total Number of Streetlights in System
Group
Relamp
90,000
Spot
Relamp
90,000
2. Average Lamp Cost
$11.50
$11.50
3. Number of Lights Cleaned & Group Re-lamped per Yr .
$18,000
$0.00
4. Cost of Labor, Truck & Components – Spot Relamp
$100.00
$100.00
5. Cost of Labor, Truck & Components – Group Relamp
$12.00
$0.00
6. Annual Spot Relamping/Cleaning Rate – Weighted
average failure rate. Data taken from lamp manufacturers
0.048
0.116
7. Estimated number of Spot Replacements per Year (#1x#6)
$4,320
$10,440.00
8. Annual Cost – Spot Relamping (#2+#4)x#7
$481,680
$1,164,060.00
mortality curves and modified for non-cycling lamp.
44
9. Annual Cost – Group Relamping (#2+#5)x#3
$423,000
$0.00
Total Cost
$904,680.00
$1,164,060.00
After a utility has adopted a group relamping program, it is important to remember that in
addition to changing out lamps on a pre-determined cycle, proper maintenance should be
performed on the luminaire and supporting pole as well. The easiest way to ensure that this
maintenance is performed correctly will be to establish an inspection checklist. The inspection
checklist needs to be developed with several important criteria in mind. First and foremost the
safety of the public and that of the maintenance workers needs to be ensured. In addition,
ensuring proper operation of the lamps so they can operate at maximum efficiency needs to be a
top priority as well since it also affects safety and security. Theoretically, 2 inspection checklists
will be prepared: a safety inspection checklist and a maintenance inspection checklist. The two
different checklists will be discussed below.
Safety Inspection Checklist
Developing a proper safety inspection checklist for street lighting maintenance is very important
to maintain adequate safety levels and reliability. An excellent guideline for safety inspection is
the California Public Utility Commission’s General Order #95, which outlines requirements for
street and decorative lighting. In addition, safety inspections should be performed whenever a
light standard is worked on. The following is a summary of checklist items with a brief
description of the task.
a) Electrical Connections - The first item to inspect should be the secondary electrical
connections that supply the luminaire, whether it is an overhead or an underground
connection. Inspect the connection to ensure proper connection with involved conductors
(i.e. squeeze on connectors, bolt on connections, crimp on connection, etc…). Also, the
maintenance personnel should look for any signs of arcing or frayed conductors. A
simple test for power lead reversal should also be performed using a multimeter rated for
the proper voltage level. Any conductors or connections in need of repair or replacement
should be addressed immediately.
b) Fuses – Fuses on the hot leg of the lighting conductor and the neutral conductor (if fused)
should be visually inspected. Caution should be exercised in the use of neutral fusing, as
the fuse may open up under a fault, while the hot leg remains energized. This may result
in the fault current path being through the metal pole to the ground rod and back to its
source.. The fuses on lighting conductors are critical in the case of a fault and are
designed to prevent damage to the luminaire and a hazard to the public. Failed fuses
should be changed out immediately.
c) Grounding – Special attention needs to be paid to ensuring that proper grounding
techniques are in use and operational at each installation. The proper bonding of metallic
street light components to the neutral and/or safety ground for each installation should be
checked for proper installation. If a separate ground rod is present for each installation,
45
maintenance personnel should check for corrosion and proper connection to the ground
wire. Any problems should be remedied immediately.
d) Security – The security of the inspection plates should be checked to make sure they still
perform their job of keeping the public out of the standard were contact with energized
conductors can occur. If the plate is faulty or inadequate, the problem should be
remedied immediately.
The following timetable for inspection is based upon the American Association of State
Highways and Transportation Officials, An Information Guide for Roadway Lighting. The
survey respondents averaged 6.67 years for inspections; Municipalities averaged every 5 years
and Investor Owned Utilities averaged 7.5 years. The timetable is:
Electrical Connections – Inspect when lamp is replaced
Fuses - Inspect when lamp is replaced
Grounding- Inspect when lamp is replaced
Security- Inspect when lamp is replaced
Operation and Maintenance Checklist
a) Lighting Controls – Photocontrols should be checked for dirt build-up, proper orientation,
and proper operation. Master controls and timers should be checked to ensure that lights
are turned on properly when operated. Faulty control devices should be repaired or
replaced immediately to ensure timely operation.
b) Check/Replace Lamps – Manufacturers can provide Lamp Lumen Depreciation curves
for the lamps that utilities use. These curves show the approximate useful life of the
lamp and its decreased light output over time. Most lamps last approximately 20,000
hours which yields about 5 years when used approximately 11 hours per day.
c) Clean Refractors – Refractors should be checked for breakage or discoloration and
cleaned during inspection. The dirt build up affects the amount of light that can pass
through the refractor, so it is important to keep these clean to ensure proper light output.
d) Check Luminaire Parts - Seals should be checked to prevent water and contaminants
from entering which could cause overheating and damage. Gaskets, wildlife shields,
filters, and hardware should be inspected for breakages, dirt build-up, or corrosion.
e) Check Pole – Lighting poles should be inspected to make sure that they are sturdy
enough to support the load of the luminaire and any wind loading on the pole.
Maintenance personnel should check for any breakage, dents, weak spots, or stresses that
may have been caused by a pedestrian or vehicle collision, mowing or trimming vehicle,
or by acts of God. Faulty poles should be replaced as soon as possible to ensure safety.
f) Wiring - Streetlight wiring is only replaced upon failure according to all survey
respondents. Replacement of only failed streetlight wiring is the recommendation set
46
forth here. However, there is an exception to this recommendation. Certain types of
underground/direct buried electrical wires are known to deteriorate more rapidly that
their original specifications. If these types of wires begin to have multiple failures
throughout the streetlight system, it might be less costly to replace all of this type of
streetlight wire under a designed replacement plan rather than wait for failures to occur.
g) Voltage – Voltage fluctuations affect light life by causing lamps to re-strike (low voltage)
or to become damaged (excessive voltage). The voltage levels on the service conductors
should be checked with a multi-meter to ensure that proper voltage levels are being
maintained. Light ballasts in most lamps are used to control the current flow in the arc
tube. Voltage fluctuations can cause permanent damage to the ballast or arc tube. The
ballasts should be checked to ensure that they are operating properly and that they are
sized correctly to the lamp wattage. Voltage problems should be remedied using prudent
engineering solutions.
h) Night Patrolling – Night patrolling is an extremely important practice if a utility wants to
be pro-active with street light maintenance and repair. Relying solely on customers and
policemen to report outages is a practice that is barely adequate and spotty at best.
Utilities should use their mapping system to plan routes for night patrolling in order to
identify burned out lamps or underperforming lamps. By being more pro-active in
identifying and repairing faulty lamps, a utility can better provide safety to its consumers
and protect themselves from liability concerns.
i) Troubleshooting – There are many different causes of failure in lamps used on utility
street lighting system. The location of the outage including address, pole number, or
relative location should be included in any paperwork so it can be added to the GIS
system for future reference. This information will also help to develop new life cycle
curves for the different types of lamps on the system. The malfunction type, such as,
Dayburner, Light Out, Light Cycles, Other Damage, should be noted for future reference.
Common causes of failure for the most common types of lamps in use are listed below8:
•
•
8
Mercury Vapor and Metal Halide Lamp Failure – The ballast is a current limiting
device that is used to control current flow. Deterioration of the electrodes in the
arc tube and on the ballast are a common cause of light impairment and failure. A
mismatch in the ballast and lamp will also cause failure. Gases or metals lost
from the arc tube through migration to the outer bulb or air leaking into the outer
bulb will cause failure. End of life arc tube rupture can cause damage to the outer
envelope.
High Pressure Sodium Lamp Failure – This lamp type is also controlled by
ballast. When a mismatch between the ballast and arc tube occurs, gases can leak
into the outer envelope, causing a failure. As these fixtures age, the voltage
required to keep the lamp operating increases beyond the capacity of the ballast
Design Guide for Roadway Lighting Maintenance (DG-4-03) by IESNA Roadway Lighting Committee
47
•
and the lamp will extinguish. Once the lamp cools, it will re-ignite, causing a
continuous cycling on and off until the lamp fails permanently.
Low Pressure Sodium Lamp Failure – Deterioration of electrodes in the arc tube
is the most common cause of failure.
Timetable for Inspection:
The following inspection timetable is based on a pro-active group relamping and maintenance
program. It is assumed that during the visit to re-lamp the fixture these inspections will be
performed. When group re-lamping is not employed, the schedule is still valid and is a prudent
program to implement for protection of the public and personnel. Several Public Utility
Commissions have intervened regarding inspection cycles, the most recent being New York.
The more stringent testing and inspection program required by the New York Public Utilities
Commission revolves around a fatal electrocution of a woman and her pet in New York City in
January 2004. The New York Public Service Commission Case 04-M-0159- Proceeding on
motion of the Commission to Examine the Safety of Electric Transmission and Distribution
Systems, is the catalyst for the inspection program. This Case set forth a requirement that all
utilities under control of the New York Public Service Commission inspect their electric
facilities on a minimum of a five year cycle. This Case is available at the New York Public
Service Commission website for complete details of the inspection requirements.
The following timetable for inspection is based upon the American Association of State
Highways and Transportation Officials, An Information Guide for Roadway Lighting. The
survey respondents averaged 6.67 years for inspections; Municipalities averaged every 5 years
and Investor Owned Utilities averaged 7.5 years. The timetable is:
Lighting Controls – Inspect when lamp is replaced
Check/ Replace Lamps – Replace based on replacement schedule
Cleaning Refractors- Inspect when lamp is replaced
Check/ Replace Luminaire Parts- Inspect when lamp is replaced
Check/ Replace Pole- Inspect when lamp is replaced. Replace only when broken.
Wiring- Inspect when lamp is replaced. Replace only when broken.
Voltage- Inspect when lamp is replaced
Troubleshooting- On an as needed basis to determine problems
Night Patrolling- On an as needed basis to determine problems
48
APPENDIX A
STREET LIGHTING SURVEY RESULTS
Submitted to:
Hi-Line Engineering, LLC
Submitted by:
Lighting Research Center
Date:
January 3, 2005
Lighting Research Center
Rensselaer Polytechnic Institute
21 Union Street
Troy, NY 12180
518-687-7100
518-687-7120 (fax)
51
SUMMARY
Background
The street lighting survey was undertaken as a means of understanding current practices
of utilities and municipalities to provide street lighting services within their designated
service areas and to determine best practices.
The Lighting Research Center (LRC) was retained as a subcontractor to Hi-Line
Engineering, LLC to conduct a street lighting best practices survey. The survey was
conducted of willing participants who attended the 2004 Street and Area Lighting
Conference. Attendees included municipality and utility representatives, as well as
outdoor lighting designers and manufacturers. This document presents the findings of the
survey and analyzes the data.
Research Objectives
The research objectives for the survey were to explore:
• Safest operating voltage level and proper wiring methods.
• Illumination levels to alleviate public safety concerns.
• Types of streetlight fixtures and structures used for long service life and low
maintenance.
• Selection practices of overhead versus underground service.
• Comparison of operating voltages (120, 240 or 480 volts).
• Standardization of inventory.
• Lighting efficiency with regards to energy use.
• Types of equipment used in maintenance and installation of streetlights.
• Procedures and methods used in installation and maintenance.
• Costs, on a per streetlight basis, for maintenance and installation.
Methodology
The LRC developed a surveying instrument to collect data regarding the specifications,
standards, installation and maintenance practices, personnel training and record keeping
of street lighting programs of selected utilities and municipalities. The survey was
reviewed, amended and approved by Hi-Line Engineering, AMP-Ohio and the City of
Columbus, Ohio prior to its distribution. All participants of the 2004 Street and Area
Lighting Conference received a survey and instructions for its completion with the
promise that the results would be made available to all who completed the survey. 50
surveys were completed. However, some of the surveys were duplicates from the same
utility or municipality. There were also some surveys from street lighting manufacturers
and consultants. The duplicates and non-street lighting entity surveys were not included
in the data analysis. 40 surveys were available for analysis. Of the 40 surveys used not
all respondents provided answers to all the questions. Conversely, some of the questions
required multiple responses from the same entity.
52
Survey responses were placed in sub-categories based on the type of entity owning the
streetlights. These sub-categories are:
• Municipalities that own streetlights – These are towns or cities that own the
streetlights within their boundaries. They do not, however, own or maintain the
electrical distribution system. They may own the wiring to the streetlights from
some distribution point of the electrical system. On the following tables, these
entities are referred to as “Municipality”.
• Cooperative Utility – These are utility companies that are organized under the
rural electric cooperative style. These entities own the streetlights and the
electrical distribution system. On the following tables, these are referred to as
“Utility – Coop”. There were insufficient responses to conduct any meaningful
analysis on this class.
• Investor owned utilities – These are utility companies that own the streetlights and
transmission and distribution facilities within their designated service areas. On
the following tables, these are referred to as “Utility – IOU”.
• Municipal utilities – These are utility companies owned by a municipality. They
provide both the electric distribution system and the streetlights to the town or
city they serve. On the following tables, these are referred to as “Utility –
Municipal”.
• Other – One entity reported itself as other. This entry refers to a municipality
where some of the streetlights are owned by the municipality and others are
owned by the local utility. On the following tables, this is referred to as “Nonutility, Other”.
Survey Demographics
Survey respondents represented most areas of the United States. The exceptions were the
northern plains and Rocky Mountain states. Most of the respondents (72%) own more
than 50,000 streetlights each. The large majority (82%) of these streetlights are high
pressure sodium. However, there still remains in use a substantial amount (11%) of
inefficient mercury vapor streetlights.
Streetlights Owned by Survey
Respondents
50%
40%
30%
20%
10%
0%
Less than
10,000
10,000 to
50,000
53
50,000 to
100,000
greater than
100,000
KEY FINDINGS
Specifications and Standards
To determine how many streetlights to place along a roadway, someone has to define the
type of road. Survey respondents indicated they either used the Illuminating Engineering
Society of North America (IESNA) definitions (48%) or the type of road is defined by
the municipality (29%). After defining the roadway, choosing and/or approving the
location of streetlights falls to the municipality in 72% of survey respondents’ cases. In
32% of these cases, the utility recommends the location of the streetlight.
How are Roadways Defined
60%
50%
40%
30%
20%
10%
0%
IESNA
National Municipality
Not
Highw ay
Classified
System
Other
Who Selects Streetlight Locations
O ther
Munic ipality
Utility
Rec ommends ,
Munic ipality
Approv es
Utility
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
Statistically accurate information regarding illumination levels by street type was not
attainable through the survey. Too few respondents indicated any design criteria for
illumination levels. This may be an indication there is no set level of illuminance based
on roadway type for most entities responding to the survey.
Continuous street lighting along roadways is not practiced except under certain specific
conditions. Only one-third of survey respondents indicated using continuous roadway
54
street lighting on collector or major types of roadways. Continuous roadway lighting on
other types of roads was used infrequently.
The most common streetlight operating voltage was 120 volts (62%) followed by 240
volts (28%). Most entities that own streetlights (82%) use individual photocells to
control the on/off function of the streetlight. The use of low mercury content lamps in
streetlights is used mostly by investor owned utilities (IOUs) and municipal utilities.
This is not true for municipalities that own streetlights.
Streetlight Voltages
70%
60%
50%
40%
30%
20%
10%
0%
120 volts
240 volts
277 volts
480 volts
Streetlight Controllers
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Photocells
Time Clocks
Master Control
Full cutoff streetlight fixtures are now mandated in the majority of jurisdictions with the
remainder of survey respondents expecting they will be mandated shortly. The most
common streetlight fixture is the cobra head (69%). When respondents were asked to
rank the criteria for selecting streetlight fixtures, quality was ranked ahead of cost.
55
Type s of Stre e tlights
80%
70%
60%
50%
40%
30%
20%
10%
0%
Cobra
Head
Post Top
Decorat ive
Shoe B ox
Ot her
Wood is still the most popular material used for dedicated streetlight poles. Mounting
heights of streetlights vary based on the location and type of street.
Types of Streetlight Poles
Other
Cast Iron
Aluminium
for High
Mounting
Aluminium
for
Decorative
Wood for
High
Mounting
Wood for
Low
Mounting
Fiberglass
for Low
Mounting
35%
30%
25%
20%
15%
10%
5%
0%
All survey respondents indicated they keep some type of streetlight records.
Computerized records account for 62% of the records. The most popular information
included within the records are streetlight location, fixture type, lamp type, lamp size,
date of installation, pole type and who pays for the use of the streetlight.
Safety codes are followed in the installation of streetlights. IOUs and municipal utilities
tend to follow the National Electric Safety Code while municipalities that own
streetlights follow either the National Electrical Code or state mandated codes. The code
that is followed sets the grounding standards that are practiced.
56
Safety Codes Used
60%
50%
40%
30%
20%
10%
0%
NEC
NESC
State
Other
Installation Practices – Overhead Distribution
Surprisingly, the survey results indicate the use of qualified high voltage linemen (58% of
respondents) to install streetlights on overhead distribution facilities. High voltage
linemen are more expensive to use than other qualified individuals.
In terms of payment, if someone is charged for the installation of streetlights on overhead
distribution facilities, it is normally the developer of the new development. This is
especially true (83%) where the municipality owns the streetlights. However, in 40% of
the cases, there are no charges for streetlight installations in overhead distribution areas.
Where the municipality owns the streetlights or for a municipal utility, dedicated
streetlight wiring is more likely to be used. Grounding of streetlights is a function of
which electrical safety code is used. Municipalities, following the NEC, will tend to use
a driven ground rod. Utilities, following the NESC, will normally tie the ground to the
neutral conductor which is attached to a ground.
Type of Grounding
60%
50%
40%
30%
20%
10%
0%
Secondary Driven Rod Equipment
Neutral
57
Neutral &
Ground
Together
None
Other
Installation Practices – Underground Distribution
Unlike overhead installation practices, the use of high voltage linemen, low voltage
linemen and a mixture of both to install streetlights in underground distribution areas is
fairly evenly split among survey respondents.
Municipalities that own streetlights are more likely to use conduit for streetlight wiring
under all circumstances. Those utilities not using conduit in all circumstances tend to use
it under paved areas and in downtown areas. The excavation for the conduit and its
installation is most like done by the developer (56%) or by the utility (36%).
The majority of streetlight owning entities (70%) charge for the installation of streetlights
on underground distribution systems in new developments. The cost is either the full
price of the installation or the differential between the overhead cost and the underground
cost. On existing streets, the municipality picks up the installation cost 40% of the time
followed by a developer 29% of the time.
Who Pays for Underground Fed Streetlights
60%
50%
40%
30%
20%
10%
0%
Utility
Developer Municipality No Charge Developer
Pay
Differential
Grounding practices, similar to overhead, follow the safety code practices being
followed. Those entities using ground rods are split as to the requirement for impedance
to ground. Forty-two percent have no impedance requirement, 29% require impedance
less than 25 ohms and 29% require impedance less than 50 ohms.
Maintenance Practices
Nearly half of the survey respondents (48%) report that maintenance of streetlights is
performed by dedicated streetlight crews. Contractors perform this function 26% of the
time and 26% of the time it is performed by regular line crews. The use of high voltage
linemen to perform streetlight maintenance was reported by 50% of respondents.
However, municipalities that own streetlights are more likely to use low voltage line
personnel.
58
Who Maintains Streetlights
60%
50%
40%
30%
20%
10%
0%
Dedicated Streetlight
Crews
Regular Line Crews
Contractors
Group relamping is only used by 38% of the respondents. All survey respondents
indicated that streetlight fixtures, poles and wiring are only replaced upon failure.
Inventories of streetlights in use are conducted by 71% of the survey respondents either
as part of any group relamping or conducted as separate inventories. Streetlight outage
reporting is predominately provided by customers (55%) and by police and a dedicated
person within the streetlight owning entity (21% each).
The annual maintenance cost per streetlight as reported in the survey varies greatly from
a low of $10 to a high of $400. The most likely costs for entities not conducting group
relamping is approximately $40.
Training
The majority of entities owning streetlights provide some type of training to their
streetlight designers, installers and inspectors. This training mostly is in the form of onthe-job training. Low voltage training is provided to some of the installers.
RECOMMENDED BEST PRACTICES
The recommendations made as part of this report reflect the results of the survey. It does
not include recommendations that are not supported by the survey outcome or were not
part of the survey.
Specifications and Standards
•
Lighting design practices need to start somewhere. The best place to start is by
defining the types of roadways within a municipality and the type of lighting that
each roadway will receive. It is recommended that municipalities define their
roadways by using the IESNA definitions or developing their own.
59
•
•
•
•
Since the municipality will pay either for the rental of streetlights from a utility or be
the owner of streetlights, it is recommended that the municipality set up a procedure
for approving the installation and location of any new streetlight requested.
The practice of continuous street lighting, as defined by IESNA, should only be
practiced along select sections of roadways where required for safety or aesthetics.
The use of full cutoff streetlight fixtures is recommended. They are already mandated
by most jurisdictions and all indications are they will be mandated in the remainder of
jurisdictions.
The keeping of streetlight records is essential. Periodic updating of these records
through physical inventory is recommended.
Installation Practices
•
•
•
Installations should be made in accordance with whichever electrical safety code the
streetlight owning entity is required to follow. This includes grounding practices.
Use of the least costly installers and maintenance personnel is recommended. This
usually means the use of low voltage qualified line personnel. The use of dedicated
streetlight crews with the proper equipment may also reduce costs provided there are
sufficient numbers of streetlights to install and/or maintain to keep a full time crew
busy.
Charges are recommended for the added cost to install streetlights in new
developments where underground electrical distribution systems exist. The added
cost should be borne by the developer.
Maintenance
•
•
•
•
Any benefits of group relamping cannot be supported by the outcome of the survey.
Dedicated streetlight maintenance crews may be warranted if sufficient streetlights
are owned by a single entity.
The annual cost to maintain street lighting in proper order should be around $40 per
streetlight owned. This is based on spot relamping only.
It is recommended to replace streetlight fixtures, poles or wiring only upon failure.
Training
•
Training of streetlight system designers, installers and inspectors is recommended to
ensure proper street lighting systems are installed and maintained. At a minimum,
installers should receive low voltage training.
60
STUDY FINDINGS
Demographic Information of Survey Respondents
Fifty surveys were completed from 40 unique streetlight serving entities. Table 1
describes the type and size of entities responding to the survey. The majority of the
respondents (24) were from investor owned utilities and the majority of those owned
greater than 100,000 streetlights each. There is a sufficient sampling of municipalities
that own streetlights and from municipally owned utilities to segment the findings by
these two subsets as well as investor owned utilities. The sample size from cooperative
utilities is insufficient to develop data for this group. However, their responses are
included in the findings from the total survey population.
Table 1: How many streetlights do you own?
Utility Types and Lights Owned
% of
Count
% of
% of
% of
group
of
Less
group 10,000 group 50,000 group
More
reporting
to
Type
Utilities than reporting to reporting
reporting than
more
10,000 less than 50,000 10,000 to 100,000 50,000 to 100,000
in
than
Group
10,000
50,000
100,000
100,000
Municipality
7
1 14.3%
2 28.6%
2 28.6%
2 28.6%
Non-utility
1
1 100%
0 0%
0 0%
0 0%
Other
Utility - Co2
0 0%
1 50%
1 50%
0 0%
Op
Utility - IOU
24
1 4.2%
1 4.2%
9 37.5%
13 54.2%
Utility 6
1 16.7%
3 50%
1 16.7%
1 16.7%
Municipal
Total
40
4 10%
7 17.5%
13 32.5%
16 40%
Survey respondents represented most sections of the United States. Only the northern
plains and the Rocky Mountain States were not represented.
61
Table 2 illustrates the type of light source used by each of the types of street lighting
entities. Over 80% of streetlights use high pressure sodium regardless of the entity type.
The largest difference between investor owned utilities (IOU) and municipal provided
street lighting appears to be in the amount of metal halide streetlights provided by the
IOUs. It is also necessary to point out there still exists large quantities of energy
inefficient mercury vapor streetlights in all entity categories but more so with municipal
providers (14%).
Table 2: Percent of streetlights by type of lamp.
Utility Types and Streetlight Types
Type
Municipality
Non-utility
Other
Utility - Co-Op
Utility - IOU
Utility Municipal
Total
%
% Metal
HPS
Halide
82% 0%
100% 0%
% Mercury
Vapor
14%
0%
%
% Low Pressure
%
Incandescent
Sodium
Other
1%
0%
2%
0%
0%
0%
80%
81%
87%
15%
11%
12%
0%
0%
0%
0%
1%
0%
0%
0%
0%
11.5%
0.1%
0.4%
0.3%
5%
7%
2%
82.8% 4.9%
Specifications and Standards of Survey Respondents
Respondents were asked to describe how or who defines different types of streets for
determining to what degree each type of street will be lighted. Table 3 depicts the
findings from this inquiry. Streets are defined using either the IESNA definition
guidelines (48%) or directly by some entity within the municipality (39%). This is true
regardless of the type of entity providing the streetlights.
Table 3: How do you define different types of roads to determine what type & how many
streetlights will be installed?
Utility Types and Highway Definitions Used
Type
Municipality
% of
% of
% of
% of
Count of
National Group
% of Group
Group
Group
Not
Group
Responses IESNA
Hwy reporting Municipality reporting
reporting Other
Classified
reporting
reporting
in Group
Sys
National
Municipality
Not
IESNA
"Other"
Hwy Sys
Classified
5
1
2 40%
0 0%
0 0%
0 0%
3 60%
0 0%
0 0%
0 0%
0 0%
1 100%
Utility - CoOp
2
1 50%
0 0%
1 50%
0 0%
0 0%
Utility - IOU
29
7
14 48%
4 57%
2 7%
0 0%
11 38%
2 29%
1 3%
0 0%
1 3%
1 14%
44
21 48%
2 5%
17 39%
1 2%
3 7%
Non-utility
Other
Utility Municipal
Total
62
As table 4 illustrates, streetlight locations, in the majority of cases (72%), are determined
by some entity within the municipality. In 32% of the cases, the utility recommends
streetlight locations to the municipality who then approves the locations.
Table 4: Who determines the number and location of streetlights on a street?
Utility Types and Streetlight Location Determiner
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
Count of
Responses Utility
in Group
% of Group
Utility
% of Group
% of Group
% of Group
where
Recommends,
where
where Utility Municipality
Other responding
Utility
Municipality
Municipality
Recommends
"Other"
Determines Approves
Determines
7
1
0 0%
0 0%
2 29%
0 0%
4 57%
0 0%
1 14%
1 100%
2
0 0%
1 50%
1 50%
0 0%
45
8
8 18%
4 50%
15 33%
2 25%
18 40%
2 25%
4 9%
0 0%
63
12 19%
20 32%
25 40%
6 10%
Data regarding illuminance levels for different types of roads was inconclusive to
determine current practices of utilities or municipalities. Most survey respondents (20 no
response and 12 illuminance levels not determined by road type) did not provide data to
this question. One respondent’s data was deemed inaccurate. The remaining data is
insufficient to reach any statistically accurate conclusions. This may be an indication the
survey respondents do not have set illuminance levels by street type. Average values
from the remaining data by type of roadway are:
Alley – 0.3 foot-candles
Local – 0.96 foot-candles
Collector – 1.0 foot-candles
Major – 1.64 foot-candles
Continuous lighting of roadways, as defined by IESNA, indicates that there is an average
illuminance or luminance level and an acceptable uniformity ratio along a portion of a
roadway based on the roadway type. Many streets do not require continuous lighting.
The survey requested respondents to identify the types of streets where continuous
lighting is used. Table 5 presents the findings on the issue of continuous lighting of
roadways. Approximately one-third of all respondents indicated continuous lighting was
practiced on collector and major road categories. Municipal owners of streetlights and
municipal utilities also had a higher response of continuous lighting on local type
roadways, 25% and 31% respectively, than IOUs at 22%.
63
Table 5: What types of streets are designed for continuous/uniform level of street
lighting?
Utility Types and Continuous Lighting Streets
Type
% of
% of
% of
% of
% of
Count of
responses
responses
responses
responses
responses
Responses Alley
Local
Collector
Major
Other
indicating
indicating
indicating
indicating
indicating
in Group
Alley
Local
Collector
Major
"Other"
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
12
3
1 8%
0 0%
3 25%
1 33%
4 33%
1 33%
4 33%
1 33%
0 0%
0 0%
3
0 0%
1 33%
1 33%
1 33%
0 0%
46
16
3 7%
0 0%
10 22%
5 31%
15 33%
5 31%
17 37%
5 31%
1 2%
1 6%
80
4 5%
20 25%
26 33%
28 35%
2 2%
The dominant voltage used for street lighting purposes is 120 volts (62%) followed by
240 volts (28%) as can be seen in Table 6. Very few municipalities or utilities use 480
volts for street lighting purposes. This is attributed to the distribution practices found
along most streets. Secondary 120/240 wiring is common along roadways. Utilities,
rather than running another set of wires at a different voltage, will tap the streetlights off
the secondaries that are found on the pole already.
Table 6: At what voltage do you operate your streetlights?
Utility Types and Operating Voltage Percentages
Type
Municipality
Non-utility Other
Utility - Co-Op
Utility - IOU
Utility - Municipal
Total
120 volts
59%
0%
70%
65%
56%
62%
240 volts
36%
100%
5%
22%
42%
28%
277 volts
0%
0%
25%
3%
0%
3%
480 volts
5%
0%
0%
10%
1%
7%
There were only seven responses to the typical streetlight lamp wattages found by type of
street. Similar to the illuminance levels by street type, insufficient data is present to
reach any statistically accurate conclusions. Given that most respondents did not provide
illuminance levels by street type, not responding to the similar question on wattage by
street type could be expected. For the data that was provided the mean wattage lamp by
street types are:
Alley – 70 watts
Local – 100 watts
Collector – 150 watts
Major – 250 watts
64
Lamps used in street lighting applications are now available with a minimum amount of
mercury. These lamps have a cost premium over the standard lamps used for street
lighting. As Table 7 indicates, most utilities (greater than 80%) have switched to the
more ecologically acceptable low mercury lamps and the remaining utilities are
considering the switch. The opposite is true for municipal owned streetlights. Most
municipalities (80%), while considering a switch to the low mercury lamps, still employ
the older technology.
Table 7: Do you use ecologically (low mercury) enhanced streetlight lamps? If no,
would you consider using ecologically enhanced streetlight lamps even if they cost more?
Q11 - Low Mercury? Consider Low Mercury?
Type
Count of
Responses in
Group
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
5
1
% Using
Low
Mercury
1 20%
0 0%
1
1 100%
0 0%
14
2
11 79%
2 100%
3 21%
0 0%
23
15 65%
8 35%
Using Low
Mercury
Considering
Low Mercury
% Considering
Low Mercury
4 80%
1 100%
Control of the on/off function of street lighting is performed predominately by a
photocell located on each streetlight. Utilities tend to use the photocell more frequently
(87% for IOUs and 83% for municipal utilities) than municipally owned street lighting
(68%). Master controllers are the second most popular means of controlling streetlights
(17%) although far behind photocells. Municipalities that own streetlights are more
likely to use master controllers than other entities. See Table 8 for details.
Table 8: How are streetlights controlled for on/off operation?
Utility Types and Automatic Control Options
Type
Municipality
Non-utility Other
Utility - Co-Op
Utility - IOU
Utility - Municipal
Total
Avg. of % Photocells
68%
20%
100%
87%
83%
82%
Avg. of % - Time
Clock
4%
0%
0%
0%
0%
1%
Avg. of % - Master
Controller
29%
80%
0%
12%
17%
17%
The cobra head style streetlight fixture represents two-thirds of all streetlights owned by
the survey respondents. This is to be expected because the cost of these fixtures is
relatively low compared to any other streetlight fixture. As more areas within a
65
municipality or utility service area are receiving underground utilities, the use of post top,
decorative and shoebox style streetlight fixtures are gaining popularity. For IOUs, the
use of these three types of fixtures is split rather evenly (8% for post top, 10% for
decorative and 11% for shoebox). Municipalities and municipal utilities tend to favor the
post top fixture over decorative or shoe box as illustrated in Table 9.
Table 9: What types of streetlight fixtures are used?
Utility Types and Streetlight Fixture Types
Type
Municipality
Non-utility
Other
Utility - Co-Op
Utility - IOU
Utility Municipal
Total
Avg. of % - Cobra Avg. of % Head
Post Top
74%
13%
90%
0%
Avg. of % Decorative
6%
10%
Avg. of % Shoebox
6%
0%
60%
67%
66%
2%
8%
20%
10%
10%
5%
28%
11%
9%
0%
5%
0%
69%
10%
8%
10%
3%
Other
0%
0%
Most (54%) of utilities and municipalities are now requiring full cutoff streetlight fixtures
be installed. The remaining survey respondents (46%) believe full cutoff street lighting
will be required soon.
Table 10: Are you required to use full cutoff streetlight fixtures?
Full Cutoff Required? Coming Soon?
Type
Municipality
Utility - IOU
Utility Municipal
Total
Count of
% of responses
% of responses
Currently
Required
Responses in
indicating
indicating
Required
Soon
Group
Currently Required
Required Soon
5
3 60%
2 40%
17
9 53%
8 47%
2
1 50%
1 50%
24
13 54%
11 46%
It appears quality of streetlight fixtures matters more in their selection process than cost,
availability, aesthetics, brand name or optics to IOUs and municipalities that own
streetlights. However, municipal electric utilities care more about cost followed by
quality. The order of importance is quality, cost, optics, aesthetics, availability and
brand.
66
Table 11: Prioritize the selection criteria for fixtures and manufacturers.
Utilities and the avg. ranking for Selection Criteria
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Average
Average
Average Average
Ranking Ranking Ranking - Ranking Brand
Aesthetics
Optics
Other
Name
4.6
3.75
4.75
3.25
Average Average
Average
Ranking - Ranking - Ranking Quality
Cost
Availability
1.5
2.4
1
1
3
4
2
5
6
1.35
2
2.26
1.25
4.17
4.33
4
4.33
4.72
5.33
3.57
3.5
2
The type of material used in dedicated streetlight poles varies greatly (see Table 12). The
primary type of pole listed as other was concrete. Wood (29%), aluminum (22%), fiber
glass (15%) and concrete are all used extensively. The only type of streetlight pole used
in infrequent locations is cast iron. Cast iron poles are the most expensive. Today’s cast
aluminum poles can mimic the decorative design of cast iron at a fraction of the cost.
Table 12: What types of dedicated streetlight poles are used?
Utility Types and Averages of Streetlight Pole Percentages
Avg.
Fiberglass
Type
for Low
Mounting
Heights
Municipality 0%
Non-utility 0%
Other
Utility - Co- 38%
Op
Utility - IOU 18%
Utility 12%
Municipal
Total
15%
Avg.
Wood for
Low
Mounting
Heights
0%
0%
Avg.
Avg.
Avg.
Avg. Cast
Wood for Aluminum Aluminum
Iron for
High
for
for High
Other
Decorative
Mounting Decorative Mounting
Fixtures
Heights
Fixtures
Heights
25%
22%
9%
3%
41%
0%
0%
2%
0%
98%
0%
55%
0%
0%
0%
8%
5%
1%
28%
14%
13%
33%
4%
16%
1%
0%
25%
24%
3%
26%
16%
6%
1%
29%
67
Streetlight mounting heights, as depicted in Table 13, are relatively consistent across all
types of street lighting entities. Overhead distribution mounting is approximately 28 feet,
residential 17 feet, downtown area 24 feet and commercial 21 feet.
Table 13: What is the standard mounting height (feet)?
Utilities and Averages of Standard Pole Mounting Heights
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
Overhead
Distribution
30
Residential
Downtown
Neighborhoods
16.6
26
20
22.5
16
27.43
29.5
16.71
18.5
27.85
16.9
Decorative,
Interstates
Commercial
22.4
41.67
40
22.5
25
23.06
25.75
21
19
34.77
48.33
23.93
21.16
37.48
Most streetlight records are computerized (63%) with a large number of entities keeping
both computer and paper records (32%). IOUs and municipal utilities are more likely to
keep computerized records (70% and 60% respectively) than municipalities that own
streetlights (43%) as is shown in Table 14.
Table 14: How is streetlight records kept?
Utilities and Method of Keeping Streetlight Records
Type
Municipality
Non-utility
Other
Utility – CoOp
Utility - IOU
Utility –
Municipal
Total
7
1
% of
% of
% of
responses
responses
responses
Paper
Both
indicating
indicating
indicating
Computerized
Paper
Both
3 43%
2 29%
2 29%
1 100%
0 0%
0 0%
2
1 50%
0 0%
1 50%
23
5
16 70%
3 60%
0 0%
0 0%
7 30%
2 40%
38
24 63%
2 5%
12 32%
Count of
Responses Computerized
in Group
Streetlight record keeping is depicted on Table 15. The information included on
streetlight records varies by entity. All survey respondents indicated the records include
the location of the streetlight. Most entities also keep records on fixture type, lamp type,
lamp size, date of installation, voltage and pole type. For IOUs and municipal utility
companies who rent lights to customers, the entity paying for the streetlight rental and the
amount of the rental are also included in most record systems.
68
Table 15: What information is kept in streetlight records?
% of Responses
Indicating
Location
records kept
Type
Count of
Responses
in Group
Municipality
7
7 100%
6 86%
Non-utility Other
1
1 100%
0 0%
Utility - Co-Op
2
2 100%
1 50%
24
24 100%
19 79%
Utility - IOU
Utility - Municipal
Location
6
Lamp Type
Type
6 100%
% of Responses
indicating Lamp
Type
records kept
% of Responses
indicating Fixture
Type records kept
Fixture Type
6 100%
Lamp Size
% of Responses
Indicating
Lamp Size
records kept
% of Responses
Indicating
Maintenance
records kept
Maintenance
Municipality
6 86%
5 71%
4 57%
Non-utility Other
0 0%
0 0%
0 0%
Utility - Co-Op
1 50%
1 50%
1 50%
19 79%
23 96%
12 50%
Utility - IOU
Utility - Municipal
6 100%
Date Initially
Installed
Type
% of Responses
indicating Date
Initially
Installed
records kept
6 100%
Date Replacement
Fixture Installed
1 17%
% of Responses
indicating Date
Replacement
Fixture Installed
Voltage
% of Responses
indicating Voltage
Municipality
4 57%
4 57%
5 71%
Non-utility Other
0 0%
0 0%
0 0%
Utility - Co-Op
1 50%
0 0%
0 0%
19 79%
11 46%
16 67%
Utility - IOU
Utility - Municipal
Type
5 83%
Notes
% of Responses
Indicating
Notes
1 17%
% of Responses
indicating Light
Rental Payor
5 83%
Pole Type
% of Responses
Indicating
Pole Type
Municipality
3 43%
14%
4 57%
Non-utility Other
0 0%
0%
0 0%
Utility - Co-Op
0 0%
100%
1 50%
Utility - IOU
8 33%
79%
18 75%
1 17%
100%
Utility - Municipal
Type
Rental
Charge
% of Responses
indicating Rental
Charge
Special Options
Installed
6 100%
% of Responses
indicating
Special
Options Installed
Other
% of Responses
Indicating
Other
Municipality
0 0%
1 14%
0 0%
Non-utility Other
0 0%
0 0%
0 0%
Utility - Co-Op
2 100%
0 0%
0 0%
13 54%
7 29%
2 8%
1 17%
0 0%
0 0%
Utility - IOU
Utility - Municipal
Table 16 indicates half of the respondents (50%) use the National Electrical Safety Code
(NESC) when constructing streetlight facilities. IOUs (63%) and municipal utilities
(56%) use NESC more so than municipal entities that own streetlights (23%). This
should be expected since utilities, in general, abide by NESC for all their construction
safety requirements. Because there are more responses to this survey question than there
are responding organizations, it is possible the responses indicate that multiple safety
codes are used within the same entity. Municipalities that own streetlights tend to use
either the National Electrical Code (31%) or state safety codes (38%). However, large
69
percentages (23%) also use the NESC. Again the response from municipalities is in line
with the code requirements for non-utility entities.
Table 16: What safety standards are followed?
Utility Types and Safety Standards Used
Count of
%
%
%
%
Responses NEC reporting NESC reporting State reporting Other reporting
in Group
NEC
NESC
State
Other
Municipality
13
4 31%
3 23%
5 38%
1 8%
Non-utility
2
1 50%
0 0%
1 50%
0 0%
Other
Utility - Co4
2 50%
2 50%
0 0%
0 0%
Op
Utility - IOU
30
8 27%
19 63%
2 7%
1 3%
Utility 9
0 0%
5 56%
3 33%
1 11%
Municipal
Total
58 15 26%
29 50%
11 19%
3 5%
Type
Installation and Installation Practices – Overhead Distribution of Survey Respondents
Surprisingly, the majority (58%) of entities responding to who installs streetlights on
overhead distribution facilities indicate they use qualified high voltage linemen. (see Table
17) High voltage linemen are expensive workers to install streetlights. Only 17% of IOUs
and municipal utilities use dedicated low voltage linemen, normally a lower cost worker.
Municipalities who own streetlights indicated they use low voltage linemen in 50% of the
cases. This is expected because high voltage lineman are normally not required within
municipalities. There are also a large number of streetlight entities (22%) that use either low
or high voltage linemen.
Table 17: What is the qualification of the overhead distribution streetlight installers?
Utilities and Qualifications of Overhead Dist Installers
Type
Municipality
Utility - CoOp
Utility - IOU
Utility Municipal
Total
% of
responses
indicating
High
Voltage
Linemen
1 25%
2 100%
Qualified
Count of
High
Responses
Voltage
in Group
Linemen
4
2
% of
Qualified
% of
responses
Low
responses
indicating Both
Voltage
indicating
Low Voltage
Linemen
Both
Linemen
2 50%
0 0%
1 25%
0 0%
24
6
13 54%
5 83%
4 17%
1 17%
7 29%
0 0%
36
21 58%
7 20%
8 22%
Who pays for the installation of streetlights on overhead distribution facilities in new
developments is depicted in Table 18. Overall, in 43% of the cases, the developer pays
70
for streetlight installation. However, in 40% of the cases, there is no charge for
streetlight installations. There are dramatic differences on who pays based on the type of
entity that owns the streetlights. For municipalities that own streetlights, developers pay
for new streetlights 83% of the time with the municipality paying 17% of the time. In the
case of IOUs, there is no charge 56% of the time and 30% of the time the developer is
charged for new streetlights. Municipal utilities also favor the developer paying for new
streetlights in 57% of the cases.
Table 18: Who pays for streetlights in new developments on overhead distribution poles?
Utility Type and Overhead Installation Payer
%
Count of
%
% reporting
No
reporting
Type
Responses Developer reporting Municipality
Municipality Charge
No
in Group
Developer
Charge
Municipality
6
5 83%
1 17%
0 0%
Utility - Co2
1 50%
0 0%
1 50%
Op
Utility - IOU
27
8 30%
4 15%
15 56%
Utility 7
4 57%
2 29%
1 14%
Municipal
Total
42
18 43%
7 17%
17 40%
The issue of dedicated streetlight wiring versus streetlights served off of existing
secondary distribution wires is split essentially evenly (49% vs. 51%) as indicated in
Table 19. Municipalities that own streetlights and municipal utilities favor dedicated
secondary wiring for streetlights (67% each) while IOUs favor serving streetlights off
existing secondary distribution systems (60%).
Table 19: Are separate/dedicated secondary wiring used for streetlights on overhead
distribution poles?
Utilities and Separate/Dedicated Secondary Wiring
Type
Municipality
Utility - CoOp
Utility - IOU
Utility Municipal
Total
Uses Separate
Does Not Use
%
or Dedicated
Separate or
responding
Secondary
Dedicated
Uses
Wiring
Secondary Wiring
6
4 67%
2
2
1 50%
1
Count of
Responses in
Group
% responding
Does Not Use
33%
50%
25
6
10 40%
4 67%
15 60%
2 33%
39
19 49%
20 51%
Streetlight grounding practices on overhead distribution systems vary by the type of
entity owning the streetlights (see Table 20). It appears utilities favor bonding the
streetlight neutral only to the secondary neutral conductor of the secondary distribution
system (45% for IOUs and 83% for municipal utilities). This practice may be linked to
71
the use of the NESC by many utilities. Twenty-one percent of IOUs responding to the
survey also use a ground rod at each overhead pole and bond both the streetlight neutral
conductor and the equipment ground to the grounding rod. Municipalities that own
streetlights appear to favor the NEC grounding requirements to bond to an equipment
ground. Again, this may be due to their use of the NEC in their construction practices.
Table 20: What type of grounding practices are employed for streetlights on overhead
distribution systems?
Count of
% reporting
Secondary
Responses in
Secondary
Neutral
Group
Neutral
Municipality
5
1 20%
Utility - Co2
1 50%
Op
Utility - IOU
33
15 45%
Utility 6
5 83%
Municipal
Total
46
22 48%
% reporting
Neutral and
Neutral and
Type
Ground
None
Ground
Together
Together
Municipality
1 20%
0
Utility - Co0 0%
0
Op
Utility - IOU
7 21%
5
Utility 1 17%
0
Municipal
Total
9 19%
5
Type
Driven Rod
% reporting
% reporting
Equipment
Driven Rod
Equipment
1 20%
1 50%
2 40%
0 0%
3 9%
0 0%
2 6%
0 0%
5 11%
4 9%
% reporting
None
Other
%
reporting
Other
0%
0%
0 0%
0 0%
15%
0%
1 3%
0 0%
11%
1 2%
Installation and Installation Practices –
Underground/Direct Buried Distribution of Survey Respondents
There is a consistency of responses from municipalities that own streetlights and
municipal utilities as to who installs streetlights on both overhead and underground
distribution systems. By comparing the responses on Table 17 (Overhead Distribution
Installers) and Table 21 below, we see identical percentages for municipalities that own
streetlights, 25% installed by high voltage linemen, 50% installed by low voltage linemen
or splicers and 25% installed by a mixture of either high or low voltage linemen. The
percentages are close to being the same for municipal utilities for both overhead and
underground distribution systems. IOUs have a shift from 54% using high voltage
linemen on overhead distribution systems to install streetlights to 25% on underground
systems. The shift is toward using either high or low voltage personnel (29% for
overhead to 42% for underground).
72
Table 21: What are the qualifications of the underground streetlight installers?
Utilities and Qualifications of Underground Dist Installers
Type
% of
% of
responses
High
Low
% of responses
% of
responses
Count of
indicating
High
Voltage
indicating Voltage
indicating Low
responses
Mixture
Responses
High
Voltage
Cable
Linemen/
Voltage
indicating
High
in Group
Voltage Linemen
Splicers
Voltage
Splicers Linemen/Splicers
Mixture
Cable
Linemen
Splicers
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
4
1
0 0%
0 0%
1 25%
0 0%
2 50%
1 100%
1 25%
0 0%
2
0 0%
2 100%
0 0%
0 0%
24
6
2 8%
0 0%
6 25%
4 67%
5 21%
1 17%
10 42%
1 17%
37
2 5%
13 35%
9 24%
12 32%
Table 22 indicates where conduit is used for streetlight wiring in underground
distribution systems. Municipalities that own streetlights have more of a tendency to use
conduit all the time (50%) followed by municipal utilities at 40% and then IOUs at 25%.
If not using conduit all the time, the entities have a tendency to use conduit under
pavement and within downtown areas. The use of conduit for streetlight wiring in
residential areas occurs only 15% of the time according to the survey respondents.
Table 22: Is conduit used for underground streetlight wiring?
Type
Municipality
Non-utility
Other
Utility - Co-Op
Utility - IOU
Utility Municipal
Total
Type
Municipality
Non-utility
Other
Utility - Co-Op
Utility - IOU
Utility Municipal
Total
Count of
% reporting
Always
Responses in
Always
Underground
Group
Underground
10
5 50%
1
1 100%
3
36
10
% reporting
Never
Underground
0 0%
0 0%
Never
Underground
0 0%
9 25%
4 40%
0 0%
0 0%
0 0%
60
19 32%
0 0%
% reporting
Under
% reporting
% reporting
Under
Downtown
Residential
Pavement
Downtown
Residential
Pavement
1 10%
2 20%
2 20%
0 0%
0 0%
0 0%
1 33%
12 33%
3 30%
1 33%
10 28%
2 20%
1 33%
5 14%
1 10%
17 28%
15 25%
9 15%
73
The dominant response as to who is responsible for installing street lighting conduit in
new developments is the developer (56%) followed by the utility (36%) according to the
results of the survey as shown on Table 23 below. When the municipality owns the
streetlights, the developer has the responsibility for the conduit installation 86% of the
time. Municipal utilities also lean toward the developer installing the conduit (67%).
IOUs are relatively evenly split between developers (47%) and the utility (41%) as to
who will install the conduit.
Table 23: Who is responsible for the installation of any required conduit in new
construction developments?
Utilities and New Const Conduit Install Responsibility
Count of
%
%
% reporting
Developer reporting
Responses Utility reporting Municipality
Municipality
in Group
Utility
Developer
Municipality
7
1 14%
0 0%
6 86%
Non-utility
1
0 0%
0 0%
1 100%
Other
Utility - Co2
1 50%
0 0%
1 50%
Op
Utility - IOU
34
14 41%
4 12%
16 47%
Utility 6
2 33%
0 0%
4 67%
Municipal
Total
50
18 36%
4 8%
28 56%
Type
The responsibility for excavation in new developments for the installation of streetlight
wiring in underground distribution areas follows closely the results found for who is
responsible for installing conduits in underground distribution areas as shown in Table
23. Table 24 shows the same percentages for who is responsible for excavation as is
shown in Table 23 when the municipality owns the streetlights. For municipal utilities
and IOUs, there is a slight shift toward the utility doing the excavation.
Table 24: Who is responsible for the excavation for the installation of streetlights and
streetlight wiring in new construction developments?
Utilities and Excavation Responsibility in New Construction
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
Count of
%
% reporting
Responses in Utility reporting Municipality
Municipality
Group
Utility
7
1 14%
0 0%
1
0 0%
0 0%
Developer
% reporting
Developer
6 86%
1 100%
2
1 50%
0 0%
1 50%
29
7
15 52%
3 43%
3 10%
0 0%
11 38%
4 57%
46
20 43%
3 7%
23 50%
74
The utility is most likely (70%) to provide and install the streetlight wiring in
underground distribution area (see Table 25 below). The exception to this response is
where the municipality owns the streetlights. In this case, the developer of the new
development is more likely to provide and install the streetlight wiring (57%) with the
utility installing the wiring 43% of the time.
Table 25: Who is responsible for providing and installing the underground wiring for
streetlights?
Utilities and Provide & Install Underground Wires
Count of
%
%
% reporting
Developer reporting
Responses Utility reporting Municipality
Municipality
in Group
Utility
Developer
Municipality
7
3 43%
0 0%
4 57%
Non-utility
1
0 0%
0 0%
1 100%
Other
Utility - Co2
2 100%
0 0%
0 0%
Op
Utility - IOU
30
23 77%
3 10%
4 13%
Utility 6
4 67%
0 0%
2 33%
Municipal
Total
46
32 70%
3 6%
11 24%
Type
Most entities (80%) that own streetlights in underground distribution areas install
separate or dedicated wires to the streetlights as depicted in Table 26.
Table 26: Are separate/dedicated secondary wiring used for streetlights in underground
distribution areas?
Utilities and Secondary or Dedicated Underground Wiring
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
Uses Separate
Does Not Use
%
or Dedicated
Separate or
responding
Secondary
Dedicated
Uses
Wiring
Secondary Wiring
7
7 100%
0
1
1 100%
0
Count of
Responses in
Group
% responding
Does Not Use
0%
0%
3
2 67%
1 33%
24
6
18 75%
5 83%
6 25%
1 17%
41
33 80%
8 20%
In new developments with underground electric distribution systems, the property
developer is most likely to pay for the installation of the streetlights in total (56%) or the
differential cost between overhead and underground streetlights (15%). Only for 8% of
the IOUs responses are no charges assessed. In some instances (12%), the municipality
75
pays for the installation of streetlights in new developments in underground distribution
areas. (See Table 27)
Table 27: Who pays for the installation of streetlights in new developments with
underground distribution?
Utilities and Underground New Dev Installation Payer
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
%
Count of
%
%
%
% reporting
No reporting
Responses Utility reporting Developer reporting Municipality
Differential reporting
Municipality Charge
No
in Group
Utility
Developer
Differential
Charge
7
1
0 0%
0 0%
6 86%
1 100%
1 14%
0 0%
0 0%
0 0%
0 0%
0 0%
3
1 33%
1 33%
0 0%
0 0%
1 33%
36
5
5 14%
0 0%
16 44%
5 100%
5 14%
0 0%
3 8%
0 0%
7 19%
0 0%
52
6 12%
29 55%
6 12%
3 6%
8 15%
When the installation of streetlights shifts to existing streets in underground electric
distribution areas, the entity responsible for costs associated with the installation of the
streetlights also shifts. Municipalities are more likely to pay any installation costs
associated with streetlights (40%) followed by the developer (29%).
Table 28: Who pays for the installation of streetlights on existing streets with
underground distribution?
Utilities and Underground Existing Streets Install Payer
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
%
Count of
%
%
%
% reporting
No reporting
Responses Utility reporting Developer reporting Municipality
Differential reporting
Municipality Charge
No
in Group
Utility
Developer
Differential
Charge
6
1
0 0%
0 0%
2 33%
1 100%
4 67%
0 0%
0 0%
0 0%
0 0%
0 0%
4
0 0%
0 0%
2 50%
1 25%
1 25%
35
6
5 14%
1 17%
10 29%
2 33%
12 34%
3 50%
3 9%
0 0%
5 14%
0 0%
52
6 12%
15 29%
21 40%
4 7%
6 12%
Municipalities that own streetlights are most likely to use driven ground rods at each
streetlight within underground distribution areas (80%). IOUs and municipal utilities are
less likely to use grounding rods (38% and 50% respectively) as Table 29 illustrates. The
use of ground rods may be tied to which safety code is used by the streetlight entity.
Municipalities that own streetlights tend to follow the NEC while utilities tend to use
NESC.
76
Table 29: Are driven ground rods used for streetlights in underground areas?
Utilities and Driven Ground
Type
Count of Responses in Group Yes
Municipality
5
4
Non-utility Other
1
0
Utility - Co-Op
2
0
Utility - IOU
21
8
Utility - Municipal
6
3
Total
35 15
% reporting Yes No % reporting No
80%
1 20%
0%
1 100%
0%
2 100%
38%
13 62%
50%
3 50%
43%
20 57%
For those entities that use grounding rods, the impedance to ground varies as described in
Table 30. Given the small response to this question, it is difficult to imply any
statistically significant conclusions.
Table 30: If driven grounds are used, what are the impedance requirements?
Utilities and Impedance of Driven Ground
Type
Municipality
Utility - IOU
Utility Municipal
Total
Count of
Responses in
Group
<= 25 % reporting <= 50 % reporting No % reporting
ohm <= 25 ohm ohm <= 50 ohm Req.
No Req.
1
5
1
1 100%
1 20%
0 0%
0 0%
2 40%
0 0%
0 0%
2 40%
1 100%
7
2 29%
2 29%
3 42%
Table 31 indicates the number of conductors distributed to streetlights in underground
distribution areas. There is no dominant answer as to how many conductors. Thirty-six
percent of respondents use a two wire conductor with a hot leg and neutral, 22% use a
three wire conductor with hot, neutral and ground and 42% use two hot legs and the
neutral.
Table 31: When serving underground fed streetlights, how many conductors are installed
between the transformer and the streetlight pole?
Utilities and No. Conductors for Underground Fed Streetlights
%
Count of Hot Leg reporting
Type
Responses
and
Hot Leg
in Group
Neutral
and
Neutral
Municipality
5
0 0%
Utility - Co2
2 100%
Op
Utility - IOU
23
8 35%
Utility 6
3 50%
Municipal
Total
36
13 36%
77
Hot Leg, % reporting Two Hot % reporting
Neutral
Hot Leg,
Legs
Two Hot
and
Neutral and
and
Legs and
Ground
Ground
Neutral
Neutral
2 40%
0 0%
3 60%
0 0%
5 22%
1 17%
10 43%
2 33%
8 22%
15 42%
Fuses are used by most of the streetlight entities (91%) responding to the survey as
shown on Table 32. The location of the fuse varies widely from the transformer or
controller (23%), the hand hole or streetlight pole base (48%) to a two location scheme of
the transformer and the pole base (20%). Municipalities that own streetlights and
municipal utilities prefer the hand hole or the pole base (100% and 57% respectively)
while IOUs have no preference.
Table 32: Where are the fuses located on underground street lighting circuits?
Utilities and Fuse Locations on Underground Circuits
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
%
Hand
%
% reporting
% reporting
reporting
Count of
Transformer
Hole
Transformer
No reporting
Transformer
Hand
Transformer
or
Responses
or
and pole
No
or
and pole
Fuses
Hole or
in Group
Controller
Pole
base
Fuses
Controller
Pole
base
Base
Base
5
1
0 0%
0 0%
0 0%
0 0%
5 100%
1 100%
0 0%
0 0%
2
0 0%
1 50%
1 50%
0 0%
29
7
4 14%
0 0%
8 28%
1 14%
10 34%
4 57%
7 24%
2 29%
44
4 9%
10 23%
21 48%
9 20%
Street Lighting Maintenance Practices
Table 33 delineates who performs routine streetlight maintenance for the different
streetlight owning entities. All entities favor the use of dedicated streetlight maintenance
crews (56% for municipalities that own streetlights, 44% for IOUs and 71% for
municipal utilities). IOUs are also more likely than the other street lighting entities to use
contractors to maintain their streetlights (32%).
Table 33: Who performs routine maintenance on streetlights?
Utilities and Performers of Routine Maintenance
%
%
Count of
Regular reporting
Dedicated reporting
% reporting
Type
Responses
Line
Regular Contractors
Crews Dedicated
Contractors
in Group
Crews
Line
Crews
Crews
Municipality
9
5 56%
3 33%
1 11%
Non-utility
1
0 0%
1 100%
0 0%
Other
Utility - Co3
1 33%
1 33%
1 33%
Op
Utility - IOU
34
15 44%
8 24%
11 32%
78
Utilities and Performers of Routine Maintenance
Type
Utility –
Municipal
Total
%
%
Count of
Regular reporting
Dedicated reporting
% reporting
Responses
Line
Regular Contractors
Crews Dedicated
Contractors
in Group
Crews
Line
Crews
Crews
7
5 71%
1 14%
1 14%
54
26 48%
14 26%
14 26%
Of the streetlight maintenance personnel used, 50% are fully qualified high voltage
linemen, 39% are low voltage linemen, 9% are other and 2% have no special
qualifications. Utilities, both IOUs and municipal, are more likely to use high voltage
linemen (52% and 71% respectively) than are municipalities that own streetlights (14%).
Municipalities that own streetlights tend to use low voltage linemen.
Table 34: What are the qualifications of personnel maintaining the streetlights?
Utilities and Qualifications of Maintenance Personnel
%
%
Count of
reporting
reporting
HV
LV
Type
Responses
Other
Linemen
HV
Linemen
LV
in Group
Linemen
Linemen
Municipality
7
1 14%
4 57%
2
Non-utility
1
0 0%
0 0%
1
Other
Utility - Co2
2 100%
0 0%
0
Op
Utility - IOU
27
14 52%
11 41%
1
Utility 7
5 71%
2 29%
0
Municipal
Total
44
22 50%
17 39%
4
%
% reporting
No Special
reporting
No Special
Qualification
Other
Qualification
29%
100%
0 0%
0 0%
0%
0 0%
4%
0%
1 4%
0 0%
9%
1 2%
Table 35 indicates most streetlight entities do not perform group relamping, 62% - no vs.
38% - yes. Municipalities that own streetlights are more likely to group relamp than the
other entities. The average group relamping cycle is 4.1 years. It does not differ greatly
from the average replacement cycle of those entities that report they do not group relamp.
Table 35: Is group relamping performed? If group relamping, what is the interval
between relamping?
Utilities and Group Relamping
Type
Municipality
Non-utility
Other
Count of
%
%
Responses in Yes reporting No reporting
Group
Yes
No
8
1
4 50%
1 100%
4 50%
0 0%
79
Avg. Interval
Reported by
those
responding
"Yes"
Avg. Interval
Reported by
those
responding
"No"
4
6
4
Utilities and Group Relamping
Type
Utility - CoOp
Utility - IOU
Utility Municipal
Total
Count of
%
%
Responses in Yes reporting No reporting
Group
Yes
No
2
0 0%
Avg. Interval
Reported by
those
responding
"Yes"
Avg. Interval
Reported by
those
responding
"No"
2 100%
25 10 40%
6
1 17%
15 60%
5 83%
4
3
4.5
42 16 38%
26 62%
4.1
4.3
A secondary method of examining the question of group relamping is by the number of
streetlights owned rather than the type of entity owning the streetlights. The low (less
than 10,000 streetlights) number of streetlights owned group appears to group relamp
more so that the other size entities.
Table 35A
Streetlights Owned and Group Relamping
Number of
Streetlights
Less than
10,000
10,000 to
50,000
50,000 to
100,000
More than
100,000
Total
Count of
%
%
Responses Yes reporting No reporting
in Group
Yes
No
Avg. Interval
Reported by
those
responding
"Yes"
Avg. Interval
Reported by
those
responding
"No"
4
2 50%
2 50%
5
8
1 12%
7 88%
4
4
13
6 46%
7 54%
3.5
4
17
7 41%
10 59%
4.33
5
42 16 38%
26 62%
4.1
4.3
Most entities that own streetlights conduct an inventory either at the time of group
relamping (16%) or as a separate activity (55%). Only 29% do not conduct any type of
inventory of installed streetlights. (see Table 36 below) However, IOUs are more likely
to conduct inventories of installed streetlights (83%) than are either municipalities that
own streetlights (50%) or municipal utilities (60%).
80
Table 36: Is inventorying of streetlight conducted periodically?
Utilities and Streetlight Inventory Practices
%
%
%
Count of
Part of
reporting
Conducted reporting
No
reporting
Type
Responses Group
Part of
Separately Conducted Inventory
No
in Group Relamping Group
Separately
Inventory
Relamping
Municipality
6
1 17%
2 33%
3 50%
Non-utility
1
0 0%
0 0%
1 100%
Other
Utility - Co2
0 0%
1 50%
1 50%
Op
Utility - IOU
24
5 21%
15 62%
4 17%
Utility 5
0 0%
3 60%
2 40%
Municipal
Total
38
6 16%
21 55%
11 29%
The majority (79%) of streetlight owning entities responding to the survey, as depicted in
Table 37, do not inspect streetlight wiring for deterioration, shorts or wear. However,
50% of municipalities that own streetlights do inspect their streetlight wiring. Of the
entities that do inspect wiring, the average frequency is 6.67 years.
Table 37: Is regular inspection of streetlight wiring for deterioration, shorts or wear
performed?
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
Count of
Responses in
Group
6
1
%
% reporting
No reporting
Yes
No
3 50%
3 50%
0 0%
1 100%
2
0 0%
24
6
4 17%
1 17%
20 83%
5 83%
7.5
39
8 21%
31 79%
6.67
Yes
Avg Frequency Reported
by those responding
"Yes"
5
2 100%
Given the number of responses to the question of who reports streetlight outages, it is
obvious that many streetlight owning entities have multiple groups reporting outages.
The most frequent group that reports streetlight outages are the general public at 55%.
Police and people within the streetlight owning entity at 21% each also play key roles in
reporting streetlight outages.
81
Table 38: What is the primary method for streetlight outage reporting?
Utilities and Primary Method of Outage Reports
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
Count of
Responses
in Group
13
1
2
%
%
%
Dedicated reporting
Customers reporting Police reporting
%
Person Dedicated
Report Customers Report Police
Other reporting
Reports Person
Outages
Report Outages Report
Other
Outages Reports
Outages
Outages
Outages
7 54%
2 15%
4 31%
0 0%
1 100%
0 0%
0 0%
0 0%
2 100%
0 0%
0 0%
0 0%
44
11
23 52%
6 55%
11 25%
2 18%
8 18%
3 27%
2 5%
0 0%
71
39 55%
15 21%
15 21%
2 3%
Survey respondents reported only replacing streetlight fixtures, poles and wiring upon
failure of the asset. (see Table 39 below)
Table 39: How often are streetlight fixtures, poles and wiring replaced?
Utilities and Fixture, Pole & Wiring Replaceme
Type
Number Reporting
Replaced on Fixture
Failure Only
Number Reporting
Replaced on Pole
Failure Only
1
6
1
6
1
2
2
2
24
6
23
6
23
6
39
38
38
Municipality
6
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
Number Reporting
Replaced on Wiring
Failure Only
The annual cost to maintain streetlights on a per streetlight basis is depicted on Table 40
below. There was a wide range of costs per streetlight per year reported in the survey
with municipalities that own streetlights reporting a higher cost than the utilities. An
expected cost might be in the $40 range based on spot relamping with a fully qualified
high voltage lineman and replacement every four years.
82
Table 40: What is the cost for maintenance per streetlight per year?
Utilities and Cost for Maintenance per Streetlight per Yr
Type
Municipality
Utility - IOU
Utility - Municipal
Range-Low
$85
$10
$25
Range-High
$400
$50
$382
Average
$260.50
$27
$203.50
Training
There is some kind of training provided to most people involved in the design of
streetlight systems. However, the majority of the training (57%) is on the job. Some
street lighting owning entities (23%) provide classroom training in addition to on the job
training.
Table 41: What type of training is given to the people designing streetlight systems?
Utilities and Streetlight System Designer Training
%
Count of
%
On
%
reporting
Type
Classroom reporting Other
Responses None reporting The
On The
in Group
None Job
Classroom
Job
Municipality
9
0 0%
6 67%
2 22%
1
Non-utility
1
0 0%
1 100%
0 0%
0
Other
Utility - Co2
0 0%
1 50%
0 0%
1
Op
Utility - IOU
30
2 7%
16 53%
7 23%
5
Utility 7
0 0%
4 57%
2 29%
1
Municipal
Total
49
2 4%
28 57%
11 23%
8
%
reporting
Other
11%
0%
50%
17%
14%
16%
Installers of street lighting equipment also receive some type of training. Thirty-seven
percent receive low voltage training and another 37% receive special training on the
installation of streetlight equipment.
83
Table 42: What type of training is given to people installing streetlights?
Utilities and Streetlight Installer Training
Type
Municipality
Non-utility
Other
Utility - CoOp
Utility - IOU
Utility Municipal
Total
Count of
Responses
in Group
5
1
%
%
Special reporting
%
%
Low reporting Correct Special
None reporting
Other reporting
Voltage Low
Install Correct
None
Other
Voltage Training Install
Training
0 0%
2 40%
2 40%
1 20%
0 0%
0 0%
0 0%
1 100%
2
0 0%
0 0%
0 0%
2 100%
24
6
2 8%
1 17%
11 46%
1 17%
9 38%
3 50%
2 8%
1 17%
38
3 8%
14 37%
14 37%
7 18%
The number of responses to the question regarding streetlight inspectors indicates some
of the streetlight owners do not have dedicated streetlight inspectors. Fifty-five percent
of those that do have inspectors do provide some type of formal training. (see Table 43
below)
Table 43: What type of training is given to inspectors of streetlight systems?
Utilities and Dedicated Inspector Training
Type
Municipality
Utility - IOU
Utility Municipal
Total
Count of
Responses in
Group
None
% reporting
% reporting
% reporting
Some
Other
None
Some
Other
4
13
3
0 0%
5 38%
2 67%
3 75%
7 54%
1 33%
1 25%
1 8%
0 0%
20
7 35%
11 55%
2 10%
84
APPENDIX B
Table of Code References
Organization
California Public
Utility Commission
Standard
General
Order #95
American
National
Standard
Practice for
Roadway
Lighting
National Fire Protection National
Agency
Electrical
Code (NEC)
National
American National
Electrical
Standards Institute/
Safety Code
Institute of Electrical
(NESC)
and Electronic
Engineers
American National
Standards Institute/
Illumination
Engineering Society of
North America
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
National Fire Protection
Agency
Rule
58.5, 78.3,
et al
RP-8-00
Addressing
Requirements for
street and decorative
lighting in the State
of California.
Basic design guide of
fixed lighting for
roadways, adjacent
bikeways, and
pedestrian ways.
90.2(A)(2)
Installation of electric conductors
along public and private premises.
C2-2002
Basic safeguard of
persons from hazards
arising from
installation, operation,
or maintenance of
electric supply and
communication lines
and associated
equipment.
Establishes the NESC as the rules
governing public or private utilities.
National
Electrical
Safety Code
(NESC)
011.A
National
Electrical
Safety Code
(NESC)
011.B
Defines the applicability of NESC
rules.
90.1(A)
Defines the purpose of the NEC.
90.2(B)(5)
Defines the point of demarcation
between the NESC and NEC rules.
011
Defines the point of demarcation
between the NEC and NESC rules.
National
Electrical
Code (NEC)
National Fire Protection National
Agency
Electrical
Code (NEC)
National
American National
Electrical
Standards Institute/
Safety Code
Institute of Electrical
(NESC)
and Electronic
Engineers
87
Organization
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
National Fire Protection
Agency
Standard
National
Electrical
Safety Code
(NESC)
Rule
Part 1,
Section 2
Definitions
Addressing
Defines terms qualified person,
service point, and utility.
100.
Definitions
Defines the term service point.
210.8
Ground- fault circuit- interrupter
protection for personnel.
232.B.4
Clearances of wires, conductors,
cables, equipment, and support arms
mounted on supporting structures for
street and area lighting.
Table 2322
Vertical clearances of equipment
cases, support arms, platforms, braces
and unguarded rigid live parts above
ground, roadway, or water surfaces.
011.C
Defines NESC as the rules covering
street and area lighting under the
exclusive control of utilities or other
qualified persons.
1910.269
This provision establishes a standard
which requires conditions, or the
adoption or use of one or more
practices, means, methods, operations,
or processes, reasonably necessary or
appropriate to provide safe or
healthful employment and places of
employment.
National
Electrical
Safety Code
(NESC)
092.B.1
Alternating current systems that are to
be grounded, 750 volts and below.
National
Electrical
Safety Code
(NESC)
097.A.2
Separation of grounding conductors.
National
Electrical
Code (NEC)
National Fire Protection National
Agency
Electrical
Code (NEC)
National
American National
Electrical
Standards Institute/
Safety Code
Institute of Electrical
(NESC)
and Electronic
Engineers
National
American National
Electrical
Standards Institute/
Safety Code
Institute of Electrical
(NESC)
and Electronic
Engineers
National
American National
Electrical
Standards Institute/
Safety Code
Institute of Electrical
(NESC)
and Electronic
Engineers
29 CFR Part
Occupational Safety
1910
and Health
Occupational
Administration
Safety and
(OSHA)
Health
Standards
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
88
Organization
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
National Fire Protection
Agency
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
Standard
National
Electrical
Safety Code
(NESC)
Rule
097.B.2
Addressing
Exception to separation of grounding
conductors.
National
Electrical
Safety Code
(NESC)
093.C.7
Bonding of equipment frames and
closures.
National
Electrical
Safety Code
(NESC)
384.A & B
Effectively grounding conductive
cases and closures of equipment.
National
Electrical
Safety Code
(NESC)
215.C.1
Effectively grounding metal or metal
reinforced supporting structures
including lamp posts.
National
Electrical
Safety Code
(NESC)
314.B
Conductive lighting poles shall be
effectively grounded.
National
Electrical
Safety Code
(NESC)
093.C.8
Grounding conductor ampacity limits.
National
Electrical
Safety Code
(NESC)
093.A
Composition of grounding conductor.
National
Electrical
Code (NEC)
National
Electrical
Safety Code
(NESC)
250.66
Size of alternating current grounding
electrode conductor.
Table 2356
Clearances in direction from line
conductors to supports and to vertical
or lateral conductors, span, or guy
wires attached to the same support.
89
Organization
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
American National
Standards Institute/
Institute of Electrical
and Electronic
Engineers
Standard
National
Electrical
Safety Code
(NESC)
Rule
350.F
Addressing
Bonding of all above ground metallic
power and communications
equipment separated by a distance of
six feet or less.
National
Electrical
Safety Code
(NESC)
441.A.1.a,
b, and c
Minimum approach distances, deenergizing and grounding of lines
above 300 volts unless insulated from
the energized part.
90
APPENDIX C
Electric Shock and the Human Being
This section discusses contact incidents; it explains methods of protection against and the
process the body goes through during such an occurrence. This section is intended to
inform the reader of the dangers of accidental contact and methods of protection that can
be utilized to protect one’s life. These concepts can be brought forward into street
lighting practices to help achieve the best system possible for safeguarding the public.
The human body, particularly the heart, is very vulnerable to electrical current. Muscle
contraction, paralysis, or heart stoppage can result from the flow of current through the
body. Burns of the skin may also occur. These effects depend upon the amount of
current and the path which the current takes through the body. The length of time during
which the current flows through the body is also a significant factor.
At currents ranging from 0.0001 to 0.001 ampere, a person my start to sense that current
flow is present. A current level of 0.001 to 0.005 ampere may cause the arm muscles to
contract and pain to begin. A current level of 0.01 ampere induces both pain and muscle
contraction. Uncontrolled contraction of muscles results from current between 0.01 and
0.02 ampere. Thus, a person cannot let go of an energized conductor.
If the current level is above 0.03 ampere, loss of voluntary controls over respiratory
muscles may occur causing breathing to stop. Normal respiration generally resumes if
the current is interrupted.
Current flow through the heart muscle will cause ventricular fibrillation. During this
condition, the muscles of the heart operate in a disorganized manner and do not pump
blood. Current levels as low as 0.075 ampere can cause this condition, but the human
body can normally tolerate this for a short time. The threshold for 60 Hz current is
proportional to body weight and inversely proportional to the square root of shock
duration time. A current of 1 ampere through the heart muscle for 1/60 of a second will
cause fibrillation.9
When a person touches an energized conductor, current flows through the body to the
ground. Some of the current may flow through the heart, depending upon how contact
occurred. The amount of current that flows depends upon the resistance of the skin, the
voltage on the energized conductor, and the ground resistance. The skin typically
provides a resistance on the order of 1500 to 5000 ohms. Skin puncture, which can result
from burns caused by electrical current flow, reduces the resistance to as low as 500
ohms.10
9
“A range of Body Impedance Values for Low Voltage, Low source Impedance systems of 60 Hz”,
M. S. Hammam, R. S. Baishiki, IEEE Transactions on Power Apparatus and Systems, Vol. PAS-102, May,
1983, pp 1097 – 1105
10
“Downed Power Lines: Why They Can’t Always Be Detected”, D. R. Volzka et al., IEEE Power
Engineering Society, February 22, 1989, p23
93
Now consider what happens when a person touches a 120 volt conductor. The typical
skin resistances noted above permit a current flow of approximately 0.024 to 0.080
amperes which can be enough to cause fibrillation given sufficient time. When a person
touches a 480 volt conductor, the current flow would be 0.096 to 0.320 amps. It should
be noted that a breaker or a fuse can not distinguish between these currents and those of
load currents and will not operate to protect the person. GFI (Ground Fault Interrupter)
outlets are designed to operate for faults of 0.005 amps and do provide protection from
electric shock.11
Figure 5 shows how skin resistance and voltage affect current flow through the body, and
the effects of these currents. This figure shows that contact with an energized power line
conductor is likely to cause ventricular fibrillation or cardiac standstill. These effects will
occur faster than the fault can be detected and the circuit isolated.12
The effects of current flowing through the body depend primarily on the frequency,
magnitude, duration, and path of the current through the body. On the basis of safety, the
50-60 Hz range of frequencies used by utilities is not a good choice for power systems,
because it is in the same range of frequency as the human heart. The body is capable of
surviving much higher levels of current at either lower or higher frequencies. The higher
threshold at higher frequencies is apparently due to the tendency of the current to remain
near the skin’s surface and away from the heart region. Research indicates that current
magnitude is not the only important factor, the shock impulse to the heart must occur
during a certain window of the heartbeat to cause ventricular fibrillation. The duration of
the shock increases the probability that the shock impulse to the heart will occur during
this window.
Some experiments also indicate that physiological factors, such as age and gender, may
be more important than body weight. Thus, the following equation yields the tolerable
body current that is recommended for all body weights:
0.116
Amperes
ts
IB = rms magnitude of the current through the body (Amps)
ts = duration of the shock (seconds)
IB =
Individual cases needs to be considered when determining risk, but how a person contacts
the electrical equipment and other factors can influence the level of risk. There are three
types of accidental shock circuits that are normally studied:
Touch Potential = voltage differences between hand and feet
Step Potential = voltage differences from foot-to-foot
11
“Downed Power Lines: Why They Can’t Always Be Detected”, D. R. Volzka et al., IEEE Power
Engineering Society, February 22, 1989, p23
12
“Downed Power Lines: Why They Can’t Always Be Detected”, D. R. Volzka et al., IEEE Power
Engineering Society, February 22, 1989, p23
94
Figure 5 Effects of Electricity on Humans
95
Metal-to-Metal Touch Potential = voltage potential difference between one hand and the
other hand
For Touch Potential and Step Potential it is necessary to be able to model the resistance
of the feet to the earth. The foot is represented as a perfectly conducting circular metallic
disk (ignore the resistance of shoes and shocks). The equation for the resistance of the
foot on uniform soil is
Rf =
ρ
ohms
4b
ρ = the resistivity of soil directly beneath the foot, in ohm-m
b = equivalent radius of the foot, in meters
If b is assumed to be 0.08m (3 in.), then Rf is approximately 3ρ in ohms. Though an
equation is given for the mutual resistance between the feet, it has negligible effects.
Thus, the resistance of two feet in parallel (touch circuit), is approximately Rf /2 in
ohms.13
Soil resistivity varies based on the type of soil and moisture content. Dry asphalt has an
average dry resistivity of 16,000,000 ohm-meters, but when wet it can be as low as
10,000 ohm-meters. Concrete has a low resistivity when wet, 21 to 63 ohm-meters.
(Note: these values for soil resistivity are typical values only). 14
The tolerable touch potential voltages can be computed for each shock situation by
multiplying the tolerable body current by the appropriate equivalent shock circuit
impedance.15 The touch potential occurs when a person touches the pole and his feet are
approximately three feet from the pole.
Step potential is normally only considered in areas of high fault currents, such as electric
power substations. Touch potential is the metal-to-metal touch voltage. For practical
purposes, the grounding system, and all objects bonded to it, may be considered at the
same potential.
Understanding Grounding
To create a circuit, a voltage potential causes current to flow through a conductor (hot
leg) to an appliance or load and return on another conductor. The voltage at the receiving
end (at the appliance) is different than at the sending end because of the voltage drop in
13
“Tennessee Valley Public Power Association Research and Development Grounding Manual”,
Allen & Hoshall, Inc., May 1996, page 46
14
“Tennessee Valley Public Power Association Research and Development Grounding Manual”,
Allen & Hoshall, Inc., May 1996, page 49, Table 4.1
15
“Tennessee Valley Public Power Association Research and Development Grounding Manual”,
Allen & Hoshall, Inc., May 1996, page 50
96
the conductor (V=IR). The amount of voltage drop is dependent on the amount of current
and the resistance of the conductor.
In the example circuit below, Figure 6, only a grounded circuit conductor (system
neutral) and a hot leg are run to a blender and a disposal in a kitchen. The case of each
device is tied directly or indirectly to remote ground. When the disposal is turned on and
current flows through the hot leg to the disposal and back through the neutral, there is a
voltage drop in the hot leg and a voltage drop in the neutral conductor. With the neutral
isolated from the case ground, no voltage potential will be measured between the
grounded cases. However, if a volt meter was placed on the load end of each neutral, a
voltage potential would be measured which will equal the voltage drop from the return
current in the neutral. The typical voltage drop allowed by the NEC is only 4 volts.
Blender
120 V
Disposal
120 V
Figure 6 Example Circuit, Equipment Case Remotely Grounded
Another situation to be concerned about occurs when the there is a short circuit in the
disposal. This would occur if the hot leg is tied or shorted to the case. In this instance,
the potential difference between the disposal case and blender case is very near the full
120 volt. The actual voltage will depend on the resistance of each case ground. In this
instance, assuming the ground resistance of the disposal case ground is 20 ohms, the
resulting fault current is 6 amps (I=V/R). This current may or may not be of a sufficient
magnitude to trip a breaker or fuse.
Another possible way to ground the cases is to bond the neutral conductor to the case, as
shown in Figure 7. This time there is no ground connection at each case. With no
current flowing, the voltage between the case of the blender and the disposal is zero.
When the disposal is turned on, the voltage difference between the disposal case and the
blender case is the voltage drop from the current in the system neutral (V=IR). The
potential difference is often too low to present a shock hazard to persons or affect
operation of conventional electrical load equipment.16 It should be noted that while this
small potential difference may not be a shock hazard to people, a similar situation within
16
“IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems”,
Gordon S. Johnson et al., 1992, page 39
97
a dairy barn, can result in a voltage potential of sufficient level to be detected by
livestock.
In this same connection, if the hot leg shorted to the case of the disposal a closed circuit
is formed from the hot leg to the case and back to the source through a low impedance
path (the neutral conductor). This low impedance path will result in high currents which
will quickly trip a breaker or fuse. There will be voltage potential between each case.
This is a result of the voltage drop from the fault current returning to the source through
the system neutral. Because the fault current is many times higher than the load current,
the potential difference can pose a hazard to humans. However, the low impedance path
will help to de-energize the fault quickly. If one touches both cases during the fault, an
alternate return path is established through the individual’s body (metal-to-metal touch
potential). Standing next to the disposal and touching it during a short circuit results in
an alternate path to ground through the body (touch potential). As long as the impedance
in the body and the remote ground (resistance beneath the feet) is sufficiently high, the
shock potential is limited but is still a cause for concern.
Blender
120 V
120 V
Disposal
Figure 7 Example Circuit, Equipment Case Bonded to System Neutral
To avoid the problems shown in Figures 4 and 5, the NEC requires that a separate
grounding conductor be run in addition to the grounded circuit conductor (neutral). For
this system, the grounding conductor is tied to neutral at the service entrance and the
grounding conductor is tied to each case. Each case can also have a direct connection to
the earth via a separate ground rod or tied to other grounding sources such as metallic
water pipes or structural steel in a building. The neutral is not connected or bonded to the
case. In fact, the neutral is treated like the hot leg and isolated from the case and from the
grounding conductor at all locations except at the service entrance. The connection is
shown in Figure 8.
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Blender
120 V
120 V
Disposal
Figure 8 Example Circuit, Equipment Case Remotely Grounded and Bonded to System
Neutral
When load current is flowing to the disposal, the cases are at ground potential because
there is no return current in the grounding conductor. A voltmeter would measure a
voltage potential between the load ends of each neutral. During a short circuit at the
disposal (the hot leg tied to the case ground), the low impedance path to the source will
result in sufficient fault current to trip a breaker or fuse. There will still be a voltage
potential during the fault between the case of the disposal and the case of the blender.
The NEC sets parameters to ensure that the impedance of the grounding conductor is low
enough to accept the available line-to-ground-fault current without creating a hazardous
impedance (IR) voltage drop. Thus the available ground-fault current of the supply
system will have a direct bearing on the equipment-grounding conductor requirements.17
The NEC also provides protection from a circuit fault by requiring ground fault
interrupters (GFI) in bathrooms, kitchens near water sources, and outside. These devices
compare the current on the hot leg to the current on the neutral conductor. If there is a
difference, the device de-energizes the circuit. The comparison of the currents allows the
device to operate very fast for very small differences in currents (less than .005 amps).
This speed and sensitivity is necessary to protect humans from electric shock.
The example based discussion to understanding grounding is critical to the design of safe
and reliable systems. These examples show how systems react under different grounding
and bonding situations, and help show advantages and disadvantages to each system.
Without this understanding, all protections available to safeguard the public may not be
utilized.
17
“IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems”,
Gordon S. Johnson et al., 1992, page 81
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APPENDIX D
Street Lighting Design Basics and Inspection Techniques
Presented by Hi-Line Engineering, LLC
Training Prerequisite
Participants involved in this training segment must have a demonstrated knowledge of the
basic concepts of electrical theory, grounding practices and principles, a minimum of 6
months construction experience, ability to interpret electrical codes, are familiar with
map and diagram reading, familiarity with the National Electrical Code and National
Electrical Safety Code.
Seminar Goals
The intent of this training is to provide inspectors, linemen, and technicians with the
techniques and tools required to safely, efficiently and effectively inspect street lighting
systems to protect the public and personnel. Insight gained from the inspection process
will benefit linemen and technicians who can later apply innovative techniques in the
field. This will be accomplished by explaining the basic concepts of street lighting, how
to apply codes and standards, verification of wiring, and bonding and grounding
requirements. Also, discussion will be held on current technology available for the
protection of the public, such as, breakaway poles and wiring. Proper wiring is
paramount for the protection of life, methods of wiring verification will be discussed and
simple measures shown for checking wiring.
It is assumed those attending the course are familiar with wiring techniques, electrical
theory, grounding and bonding practices and concepts, and electrical codes. The ability
to read maps and diagrams, as well as, construction experience will help the student
absorb the material more easily.
Training Objective
• Verification techniques for compliance with all applicable electrical codes and
utility specifications with regards to street light installation.
• Recognition of source side hot wire reversal.
• Recognition of wiring in compliance with construction drawings.
• Purpose of grounding and bonding techniques, as required by codes, to protect
employees and the public from touch potential and ground plane differential
voltages.
• Introduction to the basic theory overview of lighting concepts including lighting
levels, veiling luminance, glare, etc.
• Application of standards for offset distances from roadways and standards for
breakaway pole foundations and wiring requirements.
• Inspection techniques for concrete street lighting foundations will be explored
with common problems identified.
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•
Comprehension of design specifications including reading maps and diagrams,
and code references.
Terminal Objectives
• The student will be able to apply codes and utility specifications to an inspection
and provide feedback as to the condition of the installation.
• The student will be capable of verifying proper wiring and check for lead reversal
utilizing techniques learned.
• The student will utilize techniques from the class to verify the grounding and
bonding per applicable codes and specifications. The student shall utilize their
class experience of bonding concepts to identify possible areas of concern to be
brought forth to the design engineer.
• The student will use skills from class to aid in identifying areas where lighting
levels may not be sufficient or areas of shadows occur and bring forth these
concerns to the design engineer.
• The student will be capable of determining if street lighting poles proximity to the
roadway may pose a hazard to the public and bring concerns forward to a design
engineer.
• The student will utilize techniques obtained through training to analyze the
concrete structure for basic compliance with specifications. The student will
utilize knowledge gained in the seminar to check for common problems found in
concrete foundations.
• The student may utilize his training on breakaway pole and wiring systems,
obtained from class, to verify proper operation of the scheme. The student will be
able to recognize different types of breakaway poles and wiring schemes and
verify their proper operation.
• The student will be able to read a plan, verify proper locations and installation in
accordance to the plan.
Training Strategies
Audience Specific
Effective training takes into consideration the characteristics of the
audiences being trained and what those audiences need to learn. A
seminar can be created that is tailored to the training needed for the
intended audience to transfer the knowledge and skills identified in
this analysis.
Hands-On
The participants will acquire new skills and will practice those skills
throughout training to ensure knowledge retention. The training will
allow participants to see, hear and do (practice) the actions they will
be expected to perform.
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Focused Content
The seminar will focus on street lighting inspection process. The
course will not cover basic knowledge of electricity, plan reading, or
code implementation. The training will focus on essential skills and
concepts necessary to safeguard the public and personnel from
improper street light installation. While a training program must
teach individuals the building blocks to garner an overall perception
of street lighting, this program is not intended to make street light
designers out of the students. The participant will be required to
interpret portions of design standards to be effective. A good
example highlighting this concept is the need for a participant to
know distances from roadways in which breakaway poles or wiring
may be required. Supporting materials, in printed format, will
contain tables, charts and diagrams needed to perform an inspection.
Several real world inspection problems will be given in the
classroom as a joint exercise. In addition, individual problems will
be assigned for completion.
Due to the highly visual nature of the trainees and the dominant
mode of learning, the presentation material will include photos and
repetition of the material content. Good example problems and
situations will also be presented in both group exercises and
individual exercise. The repetition of the examples helps to
reinforce the new design skills.
Interactive
Participants involved in training will find the classroom interaction
enjoyable and valuable. The give and take of classroom interaction,
permits trainees to address unique concerns that could not be
covered using more rigid training methods. The training materials
will use creative approaches including a variety of presentation
styles, methods of instruction, realistic examples, and frequent
opportunity for trainees to assess their understanding of a topic.
Surveys of the class will help all participants to learn from their
peers in their geographic area. The methods used and lessons
learned by the individuals and their utilities will be discussed as it
relates to street lighting safety, inspection techniques, and inspection
timetables. Throughout the training, the trainee will work on
sample problems followed by a group review to give the trainee
immediate feedback informing them the answer they gave was
correct.
Modular
A modular approach to training should be used, grouping the
information given in logical and easy to understand format. This
pertains to the instructional design elements and provides flexibility
in organizing and presenting the training. This logical step by step
approach will lead the trainee from the simple concepts to the
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Modular
complex design techniques employed and there importance to the
task of street light inspection.
Timely Delivery
Ideally training should occur prior to the required use of the
information, as refresher training or support a continuous training
program. The trainees who will attend the training seminar will
already have experience in construction type activities, plan reading,
basic electricity and familiarity with applicable electrical codes and
utility standards. The seminar will be designed for those new to the
inspection of street lighting, preparing the student for exposure to
varying types, styles and design concepts. It will also be useful as a
refresher training seminar for those who have been in the field
performing these services already.
Real-Life
Scenarios
Abstract explanations and far-fetched examples will be avoided in
favor of concrete, real-life scenarios. Street lighting wiring
diagrams, utility standards, and other sources, from actual utilities,
will be utilized to show real world designs. The testing for lead
reversal on a street light, proper grounding and bonding, and
adherence to standards are all real life situations faced by inspectors.
The information will be pertinent thereby increasing retention and
recall when called upon to perform the task in the field.
Trainee Skill
Assessment
Trainee skill assessments will be conducted informally during the
course through class and individual problems. Each course will
include exercises for participants to complete specific tasks on their
own. These exercises give the user immediate feedback and allow
for clarification of concepts prior to advancing to other topics.
Trainee feedback is an important function in developing training.
The instructor will ask for feedback during and at the end of
training. A written evaluation is essential to judge if the terminal
objectives were met. Modifications can be made to the curriculum
to improve participation and retention.
Course
Evaluations
Training Curriculum
The course lesson overview/ outline are provided in this section. The following
information provides a summary of the lessons and topics for the seminar. The
curriculum is designed to meet the objectives of the training seminar.
I. Electric Shock and the Human Body
A. Affects of Electricity on the Body
i. Level of Current Required to Affect the Heart Muscle
ii. How Voltage Levels Affect Current Flow
B. Resistance of the Human Body
i. Hand to Hand Contact
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II.
III.
IV.
V.
VI.
VII.
VIII.
ii. Hand to Foot Contact
iii. Other Contact Methods
Understanding Grounding
A. Grounding Versus Bonding
B. NEC, NESC Requirements
C. Effectively Grounded
Bonding
A. Touch Potential
B. Step Voltage
C. Proximity to Other Objects
D. Effectively Grounded
Code Implementation
A. NEC, NESC, OSHA, DOT
B. Case studies
Roadway Lighting Design
A. Identify Roadway Types
i. Expressway
ii. Major
iii. Collector
iv. Local
B. Luminance Levels
C. Design Techniques
D. Light Trespass
E. Pole Offsets
i. Breakaway Pole Requirements
ii. Breakaway Wiring Requirements
F. Pedestrian Conflict Areas
Map and Diagram Reading
A. Knowledge of Symbols
B. Interpreting Schematic Diagram
C. Verify the Construction to the Drawing (Conceptualization)
Wiring and Construction Standards
A. Equipment Utilized
i. Type Poles
ii. Type Fixtures
iii. Wattage of Fixture
iv. Type Bulb
B. Voltage Levels
C. Wiring Methods
D. Mounting and Aiming
E. Methods of Control
i. Understand How This Affects Safety of Personnel and Public
Inspection Requirements
A. Verification of Proper Wiring
i. Check for Lead Reversal
ii. Use of Multimeter
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iii. Falls Within Utility or Applicable Safety Code
iv. Are Connections Proper With No insulation Exposed
v. Understand the Operation and Connections Required for
Breakaway Poles and Wiring
B. Adherence to Utility Specifications
i. All Applicable Codes
C. Determining Proper Grounding and Bonding
i. Some Form of Grounding or Bonding Present
ii. Neutral Tied to Ground Rod
D. Structural Support is Installed Properly
i. Base is Secure and Meets all Requirements of Applicable Codes
and Utility Specifications
1. Concrete Base Properly Formed and Reinforcing Rod
Present
E. Proximity to Roadway
i. Breakaway Pole and Wiring Required
F. Safety Inspection Checklist
i. Verify All Safety Critical Items are Properly Installed
G. Understand What to Look for in an Inspection
i. Perform a Mock Inspection and Critique the Process
IX. Certification Test and Practical Exam
108
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