CHAPTER 2

Miscellaneous or special loads in commercial buildings may include
small or occasional loads that do not fit into the major load groups.

A sample partial load calculation can be done for an office building to
determine the demand load.

Maximum total harmonic content of the power system waveforms
should not exceed 5% with the equipment not operating.

The demand load of a system is determined by calculating the highest
point of the load profile, which represents the maximum demand load
of the system.

Frequency variation should not be greater than ±0.5 Hz.

Line-to-line voltage balance is not usually specified, but 2.5% is a
conservative figure.

Voltage variations should be limited to +6% and -13%.

Accumulated load: The accumulation of demand load for typical
groups of loads (e.g., heating, cooling, lighting, etc.).

Load profile: The graphic representation of the demand load, usually
on an hourly basis, for a particular day.

Electric service can be any commercially available voltage with an
insulated equipment grounding conductor.

Load factor: The ratio of the average load over a designated period of
time to the peak load occurring in that period.

Larger installations may require 208 Y/120 V or 480 Y/277 V power
supply.

Gross demand load: The summation of the demands for each of the
several group loads.


Diversity factor: The ratio of the sum of the individual maximum
demands of the subdivisions of the system to the maximum demand
of the complete system.
Data processing equipment in buildings will have varying power
requirements, with smaller installations potentially being adequate
with single-phase power at 120V.

Transportation systems in buildings, such as elevators, have varying
load requirements based on the number and type needed.

Demand factor: The ratio of the maximum demand of a system to the
total connected load of the system.

Fire detection and alarm systems have small magnitudes and can
often be disregarded when calculating the building's total load.

Interval of time: Generally 15 minutes, 30 minutes, or 60 minutes.


Demand: The amount of power or energy required by a system over a
specified interval of time, expressed in various units such as kilowatts,
kilovoltamperes, kilovars, or amperes.
Fire protection systems in buildings typically require a fire pump to
maintain system pressure.

Allowing for several 2 hp duplex units is a satisfactory allowance for
the basement in terms of plumbing and sanitation equipment.

Plumbing and sanitation equipment loads in commercial buildings are
usually not large, with small sump and sewage pumps being
commonly used.

Larger heating loads should be connected to power panels to avoid
voltage drop on lighting circuits.

Some units provide hot water supply, ranging from large electric
boilers to small units.

Heating loads typically comprise one-third to one-half of the total
electrical load in a building, ranging from large heat sources to small
supplemental heaters.

Electrical engineers should collaborate with mechanical designers to
consider the use of large motors or electrical heating loads that could
impact the initial load estimate.

Small commercial buildings usually have small units with fractional
horsepower motors, while larger buildings may have larger fans and
pumps ranging from 10-75 hp or more.

The electrical load for boiler room and mechanical auxiliary
equipment typically does not exceed 5% of the total building load, but
may reach up to 10% in schools.

In absorption-based air-conditioning systems, the electrical load is
reduced.

A common practice is to multiply the total tonnage by a factor of 1.6 to
2.0 to estimate the total connected load.

Examples of applications that may require shielded enclosures
include research laboratories, computer facilities, test and
measurement laboratories, and biomedical research and treatment
rooms.
Compressors typically make up 55% to 70% of the total connected
air-conditioning load, with pumps, fans, and other components
constituting the rest.

Electrical requirements should be obtained from those responsible
for system design, as they can vary significantly based on specific
needs and technologies employed.

Shielded enclosures may be necessary for applications requiring
control of electromagnetic energy.


Inadequate grounding can lead to electrical shock hazards and noise
interference.
The power requirements for space conditioning systems depend on
factors like climate, building design, interior loads, and specialized
equipment.

Typically, 1 VA/ft² is sufficient for most commercial buildings, but
wiring is often considered.

Power required for appliances depends on the type of space usage,
and the NEC's Article 220 outlines safe demand factor use for
receptacle loads.

The NEC provides guidelines, like Article 220, for calculating lighting
loads in commercial buildings and determining feeder-circuit panel
board sizing.

Demand, or demand load, refers to the electrical load at the receiving
terminals.

Connected load is the sum of the continuous ratings of the powerconsuming apparatus connected to the system or any part thereof.

Coincident demand is any demand that occurs simultaneously with
any other demand and can also be the sum of any set of coincident
demands.

Branch-circuit load refers to the load on the portion of a wiring
system beyond the final overcurrent device protecting the circuit.

Diversity is the term used to describe the effect of total load variation
and can be expressed as a diversity factor.

Certain loads may be turned off or operated at reduced power levels,
reducing the system load.

The average load on the power system, known as the demand load, is
usually less than the total connected load and may vary depending on
the time interval over which the load is averaged.

Total Load Considerations: Adding up all connected loads in the
building may result in a seemingly larger power system capacity than
actually needed to adequately serve the loads.

An engineering study of the existing electric power distribution
system should be included in the initial planning of the building
renovation.




When renovating or expanding a building, consideration should be
given to the nature and magnitude of the additions to ensure proper
grounding and shielding.
Computers, communications equipment, and low-level electronic
systems require special analysis of the grounding system.
The use of electronic equipment in commercial buildings raises
concerns about electromagnetic hazards, pollution, and
environmental quality.


Lighting loads in air-conditioned commercial buildings typically
account for 20% - 50% of the total load, with a range of 3 - 6 VA/ft2.

Non-coincidence of many loads often invites consideration of
diversity or demand factors.

Load characteristics such as repetitive starting or cycling of a load
from lightly loaded to full load should be taken into consideration.
The electric power distribution system in a building exists to serve
the loads and electrical utilization devices.
CHAPTER 3

Mitigating harmonics is done to reduce their negative impact.

Tuned (Resonant) Filters: Designed to target and eliminate specific
harmonic frequencies by providing a low-impedance path at the
targeted frequencies.

Active Filters: Use electronic components to actively inject equal but
opposite harmonic currents into the system, canceling out unwanted
harmonics.

Band-Pass Filters: Allow a specific range or band of frequencies to
pass through while attenuating frequencies outside this band.

High-Pass Filters: Allow higher-frequency components to pass
through while blocking lower-frequency fundamental and harmonics.

Low-Pass Filters: Allow low-frequency components to pass through
while attenuating higher-frequency harmonics.

Common types of harmonic filters include passive filters, active filters,
and tuned (resonant) filters.

Harmonic filters are electronic devices or systems designed to reduce
the presence of unwanted harmonic frequencies in an electrical
system.

Loads sensitive to voltage and frequency transients should be
identified for proper protection.

The required reliability and expected continuity of service should be
identified.

It is important to consider the average usage or load factor, seasonal
and time-of-day variations, ratings of largest loads, and associated
switching requirements.

Switched loads and redistribution techniques can help balance the
load and reduce strain on the system.

Programmed loads and regenerative systems can help optimize
energy usage.

High-efficiency motors and motor-speed control can be implemented
to reduce energy consumption.

Power factor correcting equipment and power factor improvement
techniques can help improve the power factor of the total load.

Load limiters can be used to reduce the demand and connected load,
as well as allow for possible expansion.

Harmonic voltages are abnormal electrical patterns that disrupt the
standard smooth flow of electricity in a power system.

Before discussing rate structure and availability of service, the
engineer should develop a load survey to estimate initial and future
loads and their electrical characteristics.

Harmonics are integral multiples of the fundamental frequency.

Variations in single-phase loading cause the currents in the threephase conductors to be different, producing different voltage drops
and causing the phase voltages to become unbalanced.

Phase voltage unbalance in three-phase systems can be caused by the
use of four-wire, grounded-wye distribution systems and the
connection of single-phase distribution transformers.

Voltage interruptions are sudden and temporary losses of voltage,
often caused by faults, equipment failures, or lightning strikes.

Electrical noise refers to short-duration, unwanted variations in
voltage caused by electromagnetic interference (EMI) or radio
frequency interference (RFI) from nearby electrical devices.
The design of an electric distribution system should begin with a load
survey to identify the size, location, and nature of the various loads.

Momentary voltage swells can be caused by the sudden removal of a
heavy load or a fault in the power system.
Load tabulation is necessary as power systems for different buildings
vary due to different load requirements.

Voltage swells are short-lived increases in voltage above the nominal
level.

Voltage sags are short-duration decreases in voltage below the
nominal level, often caused by sudden high-current demands or faults
in the power distribution system.
Minimum service and feeder sizes ensure the safety of electrical
systems by preventing undersizing of components.

Voltage spikes are sudden, short-lived increases in voltage caused by
lightning strikes, power surges, or switching operations.
NEC Load Estimate: Calculation based on the National Electrical Code
(NEC) requirements.

Examples of momentary voltage variations include voltage spikes,
voltage sags, and voltage swells.
Final Load Estimate: Calculated from ultimate electrical and
mechanical drawings, includes motor sizes, permanent appliances,
lighting loads, receptacle estimates, and heating equipment loads.

Momentary voltage variations can damage or affect the operation of
electronic devices, causing data loss, equipment malfunctions, or
permanent damage.
Early Design Load Estimate: More accurate assessment used to
determine necessary services, utility negotiations, and choice of
distribution systems and voltages, impacting space requirements for
electrical rooms and substations.
CHAPTER 4













Each electric utility differs in rate structure, service policies, and
requirements, so it is important for the electrical engineer to contact
the utility company early in the design phase.
Useful information for electrical load requirements can be obtained
from meter readings, measurements for similar buildings, electric
utility companies, equipment manufacturers and associations, or
governmental agencies.
Data for load estimation is typically obtained from those involved in
designing the building and its integral systems, such as lighting,
heating, ventilation, air conditioning, and transportation.
Energy codes, enacted by local governments, allocate electric power
based on standards like ASHRAE/IES to promote energy conservation
and may adjust power allowances based on usage patterns.
Preliminary Load Estimate: Based on available data from existing
buildings of the same usage and square footage or volume, used for
preliminary engineering studies and cost feasibility.
The engineer should make provisions for load growth and building
expansion to ensure adequate electrical capacity and equipment
provision.
The power distribution system should provide sufficient reliability,
safety, and flexibility to accommodate changing loads and building
requirements.
Electric utility metering and billing involve various aspects such as
metering by type of premises, service voltage characteristics, meter
location, and types of metering.
Effective communication and collaboration among designers, stakeholders,
and project managers are key to navigating these factors.
The selection of a power source is determined by design engineers and
utility engineers.
An electric power supply is a device that converts electric current from a
source to the correct voltage, current, and frequency to power an electrical
load.

Maintenance facilities and cost
Communication with the local supplying utility is important to incorporate
local requirements in building plans.

Removable power circuit breaker with self-coupling disconnecting
contacts
Utility and project factors should be carefully considered throughout the
design process.

They absorb all the arc energy using a powder or sand filler around
the fusible element.
Each electric utility has different rate schedules for supplying power to
customers under various conditions.

Compliance with IEEE standards for safety and functionality.

Class L Fuses (601-6000 A)

Transformers in commercial installations are used to change voltage
levels from utility distribution voltage to a usable voltage within a
building and to reduce building distribution voltage for specific
equipment.

Applicable standards for transformers are the ANSI C57 Series and
NEMA TR and ST Series.

Power distribution apparatus includes medium- and high-voltage
fuses, metal-enclosed load interrupter switchgear, metal-clad circuit
breaker switchgear, low-voltage power switchgear and circuit
breakers, metal-enclosed distribution switchboards, primary-unit
substations, secondary-unit substations, panelboards, molded-case
circuit breakers, low-voltage fuses, service protectors, enclosed
switches, bolted pressure switches, high-pressure contact switches,
network protectors, lightning and transient protection, load transfer
devices, and interlock systems.

Substation: Application - Outdoor substations, Ratings - Single-phase
units: 750-5,000 kVA, Three-phase units: 750-25,000 kVA, Primary
Voltage Range - 2,400 V and up, Taps - Usually manually operated
when de-energized, Automatic load tap changing may be available,
Secondary Voltage Range - 480-13,800 V, Primary Connection Usually delta connected, Secondary Connection - Usually wye
connected (to ease grounding of the secondary neutral), Insulation
and Cooling - Usually liquid medium, High-Voltage Connections - On
cover-mounted bushings, Low-Voltage Connections - May be covermounted bushings

Primary-unit substation, Secondary-unit substation (power center),
Network, Pad-mounted, Indoor distribution transformers are also
used in commercial buildings.

Application: Used with their secondaries connected to mediumvoltage switchgear.

Ratings: Three-phase units rated from 1,000 kVA to 10,000 kVA.

Primary Voltage Range: 6,900 V to 138,000 V.

Secondary Voltage Range: 2,400 V to 34,500 V.

Taps:

- Usually manually changed while de-energized.

- Automatic load tap changing may be available.

Primary Connection: Usually delta connected.

Transformer Type: May be oil-filled, may use less-flammable liquid as
insulation, air insulation may be used, dry-type transformers may be
employed, cast-coil transformers may be used, gas-insulated
transformers are an option.

Primary Connection: Delta connected.

Secondary Connection: Wye connected.

Transformer Type:
The methods and formulas used in these calculations are given in IEEE Std
493 - 1990 (ANSI) and MIL-HDBK-217, Reliability for Electric and
Electronic Equipment Handbook.
Statistical analysis methods involving the probability of power failure can
be used to calculate the failure rate and forced downtime for the power
distribution system.
To ensure the reliability of a power distribution system, it is necessary to
have reliability data on the electric utility supply and each piece of
electrical equipment used in the system.
Reliability data for electrical equipment is used to calculate the failure rate
and forced downtime per year of the power system.
This quantitative comparison can be used to make trade-off decisions
involving initial cost versus failure rate and forced downtime per year.
The standard includes a quantitative comparison of failure rates and
forced downtime in hours per year for different circuit arrangements, such
as radial, primary-selective, simple spot-network, and secondary-network
circuits.
It addresses considerations for system design, equipment selection, and
operational practices to enhance the reliability and performance of power
distribution systems.
The standard provides recommendations for designing power systems
that deliver reliable and high-quality electrical power to industrial and
commercial facilities.
IEEE Std 493-1990 provides guidance and recommendations for the design
of reliable power systems in industrial and commercial settings, covering
aspects such as system planning, equipment selection, system grounding,
and protection.
Power factor correction helps reduce losses in the distribution system and
electricity bills.
Power factor correction is achieved by adding capacitors to the electrical
network to compensate for the reactive power demand of inductive loads
and reduce the burden on the supply.
Voltage at any utilization equipment should be within the guaranteed
operative range of the equipment.
Power Factor Correction: The process of improving the power factor of a
system to reduce energy losses and lower costs.
Voltage Regulation: The process of controlling the voltage of a system to
keep it within a practical range.
Remote 400 Hz UPS: A UPS system designed to provide backup power for
remote 400 Hz applications.
Point-of-Use 400 Hz UPS: A UPS system specifically designed for powering
400 Hz applications at the point of use.
Point-of-Use Redundant 400 Hz UPS: A UPS system that provides backup
power for 400 Hz applications at the point of use.
Remote Redundant 400 Hz UPS: A remote UPS system that provides
backup power for 400 Hz applications.
- May be oil-filled.
Combination UPS for Multiple-Mainframe Computer Site: A UPS system
designed to power multiple mainframe computers at different locations.
- May use less-flammable liquid as insulation.
Alternative Combination UPS for Single Mainframe Computer Site: An
alternative UPS configuration for powering multiple mainframe computers
at a single site.
- Air insulation may be used.
CHAPTER 5: Transformers and Power Distribution
Apparatus
- Cast-coil transformers may be used.

Availability and cost of space


Initial cost including installation, operational personnel and cost
- May be cover bushings.
- Dry-type transformers may be employed.
- Gas-insulated transformers are an option.
High-Voltage Connections:
- An air terminal chamber can be used.

Delta-Connected Tertiary: Delta-connected tertiary is not acceptable
with a three-legged core unless an upstream device opens all three
phases for a single-phase fault.
- Throat connections are another option.

Low-Voltage Connection: Typically a throat connection.

Circuit breaker as the main circuit interrupting and protective device

Application: Used with their secondaries connected to low-voltage
switchgear or switchboards.

Transformer Type: The transformer may be oil-filled, use lessflammable liquid as insulation, use air insulation, be dry-type, employ
cast-coil technology, or be gas-insulated.

Ratings: Three-phase units rated from 112.5 kVA to 2,500 kVA.


Primary Voltage Range: 2,400 V to 34,500 V.
Pad-mounted transformer: A type of transformer that is mounted on a
pad.

Taps: Manually changed while de-energized.


Secondary Voltage Range: 120 V to 480 V.
High-Voltage Connection: Found in an air terminal chamber and can
have pressure- or disconnecting-type connectors, or a disconnecting
device.

Primary Connection: Usually delta-connected.

High-Voltage Connection Types: Can be for single or loop feed.

Secondary Connection: Usually wye-connected.

Low-Voltage Connection: Usually made by cable at the bottom, but
can also be made by bus duct.

Transformer Type: May be oil-filled, may use less-flammable liquid as
insulation, air insulation may be used, dry-type transformers may be
employed, cast-coil transformers may be used, gas-insulated
transformers are an option.

Dry-Type Transformer: Does not have the fire hazards of oil-filled
transformers and is often mounted on building roofs for proximity to
the load center.

High-Voltage Connections: May be cover bushings, an air terminal
chamber can be used, throat connections are another option.

ANSI C57.12.22-1989 applies to oil-immersed transformers with
primary voltages of 16,340 V and below.

Low-Voltage Connection: Typically a throat connection.

Pad-mounted transformer: Type of transformer, numbered as 5 in the
list.

Application: Used with secondary-network systems.


Ratings: Three-phase units rated from 300 kVA to 2,500 kVA.
Application: Used with panelboards and as separately mounted
transformers.

Primary Voltage Range: 4,160 V to 34,500 V.

Ratings: Single-phase units range from 1 kVA to 333 kVA, while threephase units range from 3 kVA to 500 kVA.

Taps: Manually operated while de-energized.


High-Voltage Connection: Generally a network switch (on-off-ground)
or alternatively, an interrupter-type switch with or without a ground
position.
Primary and Secondary Voltages: Both primaries and secondaries are
600 V and below.

Cooling Medium: Air, which can be either ventilated or nonventilated.
Smaller units may be encapsulated.

High- and Low-Voltage Connections: Utilize pressure-type
connections for cables.

Secondary Connection: Generally an appropriate network protector
or a low-voltage power air circuit breaker designed to provide the
functional equivalent of a network protector.

ANSI C57.12.40-1990, Requirements for Secondary Network
Transformers, Subway and Vault Types (Liquid Immersed) applies to
liquid immersed, subway- and vault-type network units.

Impedances: Distribution transformers typically have lower
impedances compared to substation or secondary-unit substation
transformers.

A subway-type unit is suitable for frequent or continuous operation
while submerged in water; a vault-type unit is suitable for occasional
submerged operation.

Indoor and Outdoor Distribution Transformers:

Available at primary voltages of up to 34,500 V.

Application: Used outside buildings where conventional unit
substations may not be suitable.



Construction: Tamper-resistant construction, eliminating the need for
fencing.
Feature a basic impulse insulation level (BIL) of 150 kV.
For three-phase transformers, a common secondary voltage is
480Y/277V, which is compatible with standard three-phase motors
rated at 460V.


Primary and Secondary Connections: Made in compartments adjacent
to each other but separated by barriers from the transformer and
each other.
Phase-to-neutral 277V circuits are commonly used to serve
fluorescent and high-intensity discharge (HID) lighting.

General-Purpose Transformers:

Access: Accessible through padlocked hinged doors designed to
prevent unauthorized personnel from entering either compartment.

Commonly used for distributing power at 480 V in commercial
buildings.

Ventilation: If ventilating openings are provided, tamper-resistant
grills are used.

Secondaries are typically rated at 208Y/120 V.

Predominantly dry-type transformers.

Gauges and Accessories: Located in the low-voltage compartment.

Some smaller-sized units may come in encapsulated form.

Ratings: Units are rated from 75 kVA to 2,500 kVA.


Primary Voltage Range: 2,400 V to 34,500 V.
Primarily used for supplying power to 120 V lighting, appliances, and
receptacles in commercial buildings.
Isolating or Insulating transformers:

Taps: Taps are manually changed while the transformer is deenergized.


Secondary Voltage Range: The secondary voltage range of the
transformer is 120 V to 480 V.

Primary Connection: The primary connection of the transformer is
usually delta connected or special construction wye connected.

Secondary Connection: The secondary connection of the transformer
is usually wye connected.


Virtually all power transformers used in commercial buildings are of
the two-winding type.
Autotransformers:


One-winding type transformer.
Advantages of Two-Winding Transformers:

Provide positive isolation between the primary and secondary circuits.




Desirable for various reasons, including safety, circuit isolation,
reduction of fault levels, coordination, and reduction of electrical
interference.
Applications include x-ray machines, laboratories, electronic
equipment, and special machinery.
Health care applications are detailed in IEEE Std 602-1986, IEEE
Recommended Practice for Electric Systems in Health Care Facilities
(ANSI).
Transformer specification: The "kVA" rating of a transformer stands
for kilovolt-amperes and represents the apparent power rating of the
transformer.

Segregate Circuits for Sensitive Loads: Separate heavy variable loads
from more sensitive loads and consider using a separate transformer
or secondary-unit substation for the sensitive loads.

Use Voltage Regulating Supplies for Sensitive Loads: Employ voltage
regulating supplies specifically for sensitive loads to maintain
consistent voltage levels.

Typical impedance values for power transformers are outlined in
Table 34 for self-cooled transformer kVA ratings.

These typical impedance values have a tolerance of ±7.5% according
to IEEE C57.12.00-1987 (ANSI) standards.

The kVA rating indicates the maximum amount of power that the
transformer can handle without exceeding its designed capacity.

Nonstandard impedance values may be specified, resulting in higher
costs or specific performance requirements.

Transformers are available in various kVA ratings to suit different
applications and power distribution needs.

Impedance values for small transformers can vary considerably
between manufacturers, so it is advisable to consult manufacturers'
bulletins for specific values.

Table 33 gives the preferred kVA ratings of both single-phase and
three-phase transformers according to IEEE C57.12.00-1987, IEEE
Standard General Requirements for Liquid Immersed Distribution,
Power, and Regulating Transformers (ANSI).

Transformers are manufactured with different insulation material
systems, categorized into different classes.

Performance Data Reference Temperature: Transformers with lower
conductor losses and corresponding lower temperature rises are
available, which can lead to longer life expectancy and reduced
operating costs.

Class 105 Insulation System allows for a 55 °C temperature rise above
the reference temperature, with a total ultimate temperature limit of
105 °C.

Class 120 Insulation System permits a 65 °C temperature rise with a
total permissible ultimate temperature of 120 °C.

Class 150 Insulation System allows an 80 °C temperature rise.
440Y/254V (Three-Phase, Four-Wire): Features a line-to-line voltage
of 440V and a line-to-neutral voltage of 254V, used in larger industrial
applications.

Class 185 Insulation System permits a 115 °C temperature rise.

Class 220 Insulation System allows a 150 °C temperature rise.

380/220V (Three-Phase, Four-Wire): Has a line-to-line voltage of
380V and a line-to-neutral voltage of 220V, commonly used for larger
commercial and industrial facilities.

The specific materials or combinations of materials included in each
insulation material class are specified in IEEE C57.12.00-1987 (ANSI)
standards.

480Y/277V (Three-Phase, Four-Wire): Represents a line-to-line
voltage of 480V and a line-to-neutral voltage of 277V, commonly used
in larger commercial and industrial settings.

Transformer sound levels can be an issue in commercial building
interiors, particularly in areas where a quieter environment is needed,
such as conference rooms and certain office spaces.

240V (Single-Phase): Used in smaller commercial establishments for
powering lighting, small appliances, and general electrical loads.

Technical specifications may require transformer sound levels to be
lower than the levels specified in tables in order to meet specific noise
reduction goals.

Voltage Taps: Used to change the ratio between high-voltage and lowvoltage windings in transformers.

To minimize the effects of transformer sound levels, several measures
can be taken, including isolating transformers in separate rooms,
avoiding direct attachment, using sound-isolating pads and vibration
dampers, and avoiding plenums and stairwells.

Smaller transformer sizes typically apply to lower voltages, while
larger sizes are for higher voltages.

Voltage ratings and ratios should be selected based on available
standard equipment as indicated in manufacturers' catalogs.

Common Secondary Voltages in Commercial Projects: 208Y/120V,
480Y/277V

220/127V (Three-Phase, Four-Wire): Consists of a line-to-line voltage
of 220V and a line-to-neutral voltage of 127V, commonly used in
commercial buildings for equipment and lighting.


Manual de-energized tap changing is commonly used to adjust for
differences between transformer ratio and system's nominal voltage.

Taps are classified as underload and no load.


Taps on transformers can be adjusted even when the transformer is
energized and under load to compensate for significant fluctuations in
the supply voltage.
For large transformers, flexible connections from the transformer to
long busway runs can be provided to reduce the transmission of
vibrations and noise.

Air from transformer vaults should be directly exhausted outdoors to
prevent the accumulation of hazardous gases or smoke in indoor
spaces.

Preference for Dry-Type Transformers: In situations where fire and
smoke considerations are of paramount importance, dry-type
transformers are usually preferred over liquid-filled transformers,
including less-flammable liquid-insulated types.

Transformer Protection: Well-designed transformer protection
systems can minimize the extent of damage in the event of a fault or
failure, regardless of whether the transformer is dry-type or liquidfilled.

Tap changes are more commonly used in outdoor substations with
transformers that have a capacity of over 5000 kVA.

Load tap changers can be controlled automatically or manually.

Automatic control systems are often used to continuously monitor
and adjust the taps to maintain a stable output voltage, while manual
control can be used for occasional adjustments.

Transformer tap changes can only be performed when the
transformer is deenergized for safety reasons.

Most liquid-filled and sealed-type transformers are equipped with an
externally operated tap changer with a lockable handle.

Both dry-type and liquid-filled transformers can exhibit failure modes
such as burning and generating smoke.

In very small liquid-filled transformers and most ventilated-dry-type
transformers, tap changes are adjusted by moving internal links
accessible through a removable panel on the transformer's enclosure.

Dry-type transformers, including cast-coil types, can burn when
subjected to faults for an extended period.

Liquid-filled transformers can burst, burn, and generate smoke.

Request Utility Power Supply Improvement: Ask the utility provider
to improve the regulation of the power supply to stabilize voltage
levels.

In critical areas or locations where transformer failures can have
severe consequences, provisions should be made to address rare
failure modes.

This may include fire suppression systems, ventilation systems, and
other safety measures.

Voltage and BIL Ratings: Cast-coil transformers are available with
primary voltage ratings up to 34.5 kV and BIL ratings up to 200 kV,
making them suitable for various voltage levels.

Alternative to Liquid or Gas-Filled Transformers: Cast-coil
transformers are a good alternative to liquid-filled or gas-filled units,
particularly in indoor or rooftop applications where space or
environmental considerations are important.

The effects of transformer failures are not mentioned in the given text.

Harmonic currents generated by nonlinear loads such as computers,
variable speed drives, electronic ballasts, HID lighting, arc furnaces,
and rapid mode switching devices can impact transformer windings.

Specifying %IR, %IX, and %IZ is required when paralleling
transformers to address the effects of harmonics.

Forced Air Cooling Option: Cast-coil transformers can be forced air
cooled to increase their self-cooled ratings by 50%.
Recent developments have highlighted transformer failures due to
nonlinear loads and the introduction of third and higher harmonics.

Totally enclosed, nonventilated-dry-type transformers are
constructed similarly to ventilated-dry-type transformers.

The enclosure of these transformers contains air, allowing them to
have the same BIL capabilities as ventilated-dry-type transformers.

They can be installed both indoors and outdoors, making them
suitable for areas with a corrosive or dirty atmosphere.

These transformers can be equipped with fans for forced air cooling,
which increases their capacity by a minimum of 25% and allows them
to handle higher loads.


Primary circuit parts enclosed by grounded metal barriers

Consider specifying special transformers designed to withstand and
mitigate the effects of harmonic currents and fluxes for reliable
performance in the presence of nonlinear loads.

Liquid-filled transformers are a type of transformer construction.

Liquid-filled transformers have windings contained in a sealed tank
filled with insulating liquid, serving as both insulation and a cooling
agent.


It is generally advisable to avoid using liquid-filled transformers in
commercial buildings unless they use nonflammable or lessflammable liquids and meet specific safety requirements.
Transformers require temperature measurement equipment and
controls to monitor winding temperatures and ensure safe operation.

Temperature measurement equipment is used to determine the
temperature of the transformer windings.
The insulating liquid provides insulation between winding sections
and also acts as a cooling medium, dissipating heat from the windings.

Regular maintenance of the insulating liquid is crucial to keep it clean
and moisture-free, as moisture can enter through leaks or humidity in
the surrounding air.
Temperature controls are linked to cooling systems, trip mechanisms,
or alarm devices to activate them if the temperature exceeds safe
limits.

Embedded temperature detectors are commonly installed within each
low-voltage winding to prevent the ultimate temperature of the
insulating system from being exceeded.

Applicable standards for medium- and high-voltage fuses are ANSI
C37.46-1981 and NEMA SG2-1986.

Distribution fuse cutouts have characteristics such as dielectric
withstand strengths, application primarily on distribution feeders and
circuits, mechanical construction adapted to pole or cross arm
mounting, and operating voltages corresponding to distribution
system voltages.

A distribution fuse cutout consists of a mounting (insulating support)
and a fuse holder.

Power fuses are identified by their dielectric withstand strengths,
application in various electrical systems, and adaptable mechanical
construction.

Power fuse components include the mounting structure, fuse holder
or end fittings, and the refill unit or fuse unit.

The refill unit or fuse unit contains the fuse element that breaks or
interrupts the circuit when excessive current flows through it.

Blown Fuse Indicators provide a visual signal when a power fuse has
operated or "blown," helping to identify faults in the electrical system.

Indoor Mountings are specialized configurations of power fuses
designed for indoor use in electrical systems, suitable for mediumvoltage applications with a maximum voltage of 29 kV.

Early power fuses used fiber lining and had limited interrupting
capacity, making them unsuitable for indoor or enclosed use.

In the 1930s, solid boric acid power fuses were developed, using
densely molded boric acid powder in the interrupting chamber.

When the fusible element melts, it generates non-combustible, deionized steam to interrupt the circuit.



Periodic testing for dielectric breakdown voltage and neutralization
number helps extend the transformer's lifespan.

Dry-type transformers use air instead of insulating liquid.

Transformers rated for lower temperatures can offer improved
efficiency, overload capability, and longer lifespan.

IEEE PC57.12.58 provides guidance for conducting transient voltage
analysis of dry-type transformer coils to ensure the insulation system
can withstand repetitive transients.

Ventilated-Dry-Type Transformers have a sheet metal enclosure for
mechanical protection and safety.

Ventilating louvers allow for thermal air circulation over the windings.

Fans can be added to increase the full load rating.

They are typically installed indoors and require periodic cleaning and
a clean ventilating air supply.

They can also be built with special enclosures for outdoor use,
matching the BIL (Basic Impulse Level) of liquid-immersed
transformers.



It is recommended to perform Megger testing before energizing after
lengthy shutdowns or periods of exposure to moisture to ensure
insulation integrity.
Sealed-dry-type transformers are constructed in a manner similar to
ventilated-dry-type transformers.
The enclosing tank of a sealed-dry-type transformer is sealed and
operated under positive pressures, filled with nitrogen or another
dielectric gas.

Heat generated in the windings of the transformer is transferred to
the gas within the sealed housing, conducted to the tank, and
dissipated to the surrounding air.


Sealed-dry-type transformers can be installed both indoors and
outdoors, suitable for areas with a corrosive or dirty atmosphere
where a ventilated-dry-type transformer would be impractical.
Solid boric acid power fuses have higher interrupting capacity,
produce less noise, and require less exhaust gas clearance.

They can be used indoors or in enclosures with exhaust control
devices for quiet operation.
Encapsulated Windings: Cast-coil transformers have both primary
and secondary windings encapsulated in reinforced epoxy resin.

Solid material boric acid power fuses are widely used in utility,
industrial, and commercial power distribution systems.

Current-limiting power fuses do not expel gases during operation.


Ideal for Harsh Environments: Cast-coil transformers are suitable for
applications where moisture or airborne contaminants are a concern
due to the excellent protection provided by epoxy resin.

Current-limiting fuses provide effective current limitation when the
overcurrent greatly exceeds the fuse ampere rating.

This reduces stresses and potential damage in the circuit up to the
fault point.

However, for lower overcurrent values, they may not achieve current
limitation.

Current-limiting fuses can be safely used indoors or in enclosures and
require standard electrical clearances.

They are commonly used for the protection of transformers and in
high-voltage motor starters.

Electronic power fuses are a recent technological development.

They combine features and benefits of fuses and relays.

Electronic power fuses offer coordination and ratings that other
power fuses cannot achieve.

They consist of two main components: an electronic control module
and an interrupting module.

The electronic control module defines time-current characteristics
and provides the energy for tripping.

This allows for various tripping options, including instantaneous or
time-delayed tripping.

Only the interrupting module needs replacement after fuse operation.




Fuses are used for various applications.

Metal-enclosed interrupter switchgear is used for switching and
overcurrent protection in medium-voltage applications.

It uses interrupter switches and power fuses for protection and
control.

Interrupter switches are air switches equipped with interrupters to
make or break specified currents.

Interrupter switchgear can also provide ground-fault protection for
resistance-grounded systems.

Rated maximum voltages range from 4.8 kV to 38.0 kV with various
main bus ratings.

Interrupting ratings are determined by the power fuses, which are
available in a wide range of current ratings and time-current
characteristics.

Interrupter switches can be manually or automatically operated and
are available with vacuum or SF6 gas interrupting mediums.

SF6 interrupter switches cover all medium-voltage ranges, while
vacuum switches are available up to 35 kV.

Interrupter switches can be used in combination with power fuses to
achieve higher ratings than when used alone.

Metal-enclosed interrupter switchgear is available in the range of 534.5 kV.
High-Voltage, Fiber Lined Power Fuses: Primarily used in outdoor
applications at sub-transmission voltage levels.

Automatic control devices can be integrated into metal-enclosed
interrupter switchgear with motor-powered switch operators.
High-Voltage, Solid Material, Boric Acid Fuses: Available in two styles:
end fitting and fuse unit style, and fuse-holder and refill unit style.
End fitting and fuse unit style used outdoors at various voltage levels,
including sub-transmission and distribution, and indoors in metalenclosed interrupter switchgear, vaults, and pad-mounted switchgear.
Fuse-holder and refill unit style suitable for medium- and highvoltage distributions, both indoors and outdoors.

These devices enable automatic source transfer in case of faults or
outages, enhancing service continuity in primary-selective systems.

Optional features include manual or automatic back transfer, time
delay on transfer, and lockout on faults.

Switch operators can be disconnected from switches for testing
without interrupting power to the load.

Metal-enclosed interrupter switchgear is available in 5-34.5 kV.

Metal-enclosed interrupter switchgear may include instrument
transformers, voltage and current sensors, meters, and other auxiliary
devices.

Motor-powered switch operators allow remote operation of the
interrupter switches.

Blown fuse indicators are provided for visual checking of fuses while
in their mountings.

Metal-enclosed interrupter switchgear should comply with relevant
standards and codes, such as the NEC (National Electrical Code)
Article 710-21(e).

Interrupter switches should safely withstand the effects of closing,
carrying, or interrupting all possible currents up to the assigned
maximum short-circuit rating.

Voltage ratings: 4.16–34.5 kV

Interrupting ratings: 8.8 kA at 4.16 kV to 40 kA at 34.5 kV

Continuous current ratings: 1200 A, 2000 A, 3000 A, 3750 A
Current-Limiting Power Fuses: Used for protecting auxiliary power
transformers, small power transformers, and capacitor banks. Also
available for medium-voltage transformers with high interrupting
ratings. Some are designed specifically for high-voltage motors.

Electronic Power Fuses are suitable for service entrance protection
and coordination of commercial distribution circuits.

Circuit instruments, relays, and control switches mounted on a
control panel

They have high current-carrying capability and unique time-current
characteristics for coordination with overcurrent relays and load-side
feeder fuses.

Electronic Power Fuses are ideal for load feeder protection due to
their high continuous and interrupting ratings.

Power fuses are used as primary-side overcurrent protective devices
for transformer banks.

Power fuses are suitable for transformer banks rated up to 161 kV
with a maximum rating of 15,000 kVA.

Power fuses have high short-circuit interrupting capability and fast
operation to clear faults at the transformer.

Power fuses serve as backup protection in case of secondary
overcurrent protective device malfunctions.

Potential transformers and control power transformer fuses in
drawout assemblies

Power fuses are used to protect instrument transformers and
capacitor banks in addition to main power transformers.

Automatic shutters to shield stationary primary contacts

Interlocking features for proper operation sequence

Overcurrent protective devices at primary voltages have several key
functions, including interrupting high overcurrents, acting as backup
protection, opening circuits during overcurrent conditions, and
coordinating with upstream and downstream protective devices.

Draw out feature for easy inspection and maintenance

Separable main and secondary disconnect contacts for connected, test,
and disconnect positions

Insulation is potential tracking-resistant and flame-retardant

Types of medium-voltage power circuit breakers include minimumoil, air-type, SF6-type, and vacuum-type.

Vacuum and SF6-type breakers are common through 15 kV.


Modern medium-voltage power fuses are suitable for providing
protection and coordination in various types and sizes of distribution
systems.
Switches can be applied outdoors in vaults or within metal-enclosed
interrupter switchgear.

Vacuum-type and SF6-type breakers offer advantages in reducing
transient voltage surge effects.

Metal-enclosed distribution switchboards are commonly used in
commercial buildings for distribution at 600 V and below.

Considerations for transient over voltages caused by high-speed
circuit interruption.

They serve as service entrance, power, or lighting distribution
equipment.

Vacuum-type and SF6-type breakers offer advantages in reducing
transient voltage surge effects.

They can be used as the secondary sections of unit substations.


Metal-clad circuit breaker switchgear operates at voltages ranging
from 5-34.5 kV.
They are available in a wide range of protective devices and single- or
multiple-section assemblies.


Metal-enclosed, low-voltage power switchgear and circuit breakers
operate at 600 V.
Service capacities typically range from 40 A to 4000 A, with smaller
service capacities recommended over 4000 A equipment.


Air-type circuit breakers are used for low-voltage circuit protection
and control.
Compliance with NEMA PB2-1989 (Deadfront Distribution
Switchboards) is required.


Drawout switchgear offers flexibility and complex control circuitry.
Ground-fault protection is recommended for grounded wye systems
and required for services over 150 V to ground with a disconnecting
mean rated 1000 A or more.

Used in multiple-bus arrangements for redundancy.


Available in indoor and outdoor construction.
Automatic transfer switches for main and emergency sources are
provided as complete packages with power and control features built
into the assembly.

Compliance with ANSI and IEEE standards.


Air-type circuit breakers are housed in compartments that are
isolated from each other and the bus area.

Various ANSI sizes are available for circuit breakers, such as 225 A,
600 A, 1600 A, etc.
Components of metal-enclosed distribution switchboards include
service protectors, molded-case circuit breakers, fusible switches,
motor starters, low-voltage ac power circuit breakers, bolted pressure
and high-pressure switches, transfer devices or switches, and
instrumentation, metering, and relaying equipment.


Circuit breakers can be electrically or manually operated and may
have additional devices like shunt trip and undervoltage.

There are separable main and secondary disconnect contacts for
different positions.
Construction features of metal-enclosed distribution switchboards
include front accessibility, installation against a wall, all connections
made from the front, multiple-section switchboards with lined-up
backs, enclosure on all sides except the bottom, maximum rating of
2000 A, no drawout low-voltage ac power circuit breakers as branch
devices, and no availability of load-side risers.

Compartments are provided for meters, relays, instruments, etc.


Potential and control power transformers are front accessible.

The rear section is dedicated to the main bus, feeder terminations,
wiring, and terminal blocks.
Rear Accessible — Front Connected: Designed to be free-standing,
with rear accessibility for main connections and maintenance, and
front accessibility for line and load connections for branch devices.
Cross bus is located behind the branch devices and is accessible only
from the rear. Multiple-section switchboards have fronts lined up and
are capable of accepting all components.

The bus work can be made of aluminum or copper, and the circuit
breaker terminals are rear-accessible.

Some switch designs may include integral ground-fault sensing
capabilities.

Control wiring is extended to terminal blocks for remote control and
intercompartment wiring.


The power switchgear and circuit breakers are metal-enclosed and
operate at low voltage (600 V).
Rear Accessible — Rear Connected: Designed to be free-standing,
with rear accessibility for main connections and maintenance. All line
and load connections for branch devices are made from the rear, and
all cross bus and line and load connections for branch devices are
accessible only from the rear. Multiple-section switchboards have
fronts lined up and are capable of accepting all components.

Long-life, quick-make and quick-break switching devices with
overload and instantaneous trip units.

Primary-unit substations transform power from high or medium
voltages to a voltage above 1000 V.

They provide protection and control for lower voltage feeder circuits.

These substations are commonly used in commercial buildings to
convert medium-voltage services to lower voltages, especially for
powering large motors.

Primary-unit substations are typically combinations of transformers
and metal-enclosed interrupter switchgear or power circuit breaker
switchgear.

Short-time rating allows selective systems.

Open construction for easy maintenance and replacement.

Suitable for switchgear compartments or enclosures with deadfront
construction.

Field-adjustable tripping units, interchangeability within frame sizes.

Static-type tripping units available for added selectivity.

Can be used with integral current-limiting fuses for higher
interrupting capacity.

They can be configured for indoor or outdoor use and are adaptable
to various power distribution circuit arrangements.

Selection of Circuit Breaker Tripping Characteristics: Service
continuity depends on coordination between circuit breaker tripping
characteristics.

Secondary-unit substations transform power from the 2300-35,000 V
range down to 600 V or lower.

They provide protection and control for low-voltage feeder circuits.

Design goal is a fully selective system.


Main circuit breakers equipped with long- and short-time delay trip
devices.
Secondary-unit substations are composed of three major sections
available in various forms for indoor and outdoor applications.


Feeder circuit breakers equipped with long-time delay and
instantaneous functions, or both if required.
There are four commonly used basic circuit configurations: simple
radial system, secondary-selective system, primary-selective system,
and secondary-network system.

Selective system ensures only the circuit breaker nearest the fault
trips, maintaining service continuity.

This section is designed for use with simple radial, secondaryselective, or secondary-network systems.

Metal-enclosed, low-voltage 600 v power switchgear and circuit
breakers.

It typically includes one fuse and a two-position (open-close) 5 kV or
15 kV interrupter switch.

Dual-element time delay fuses provide protection for both motors and
circuits and open the circuit on long continued overcurrent.

Current Rating: The maximum current in amperes that a fuse can
carry continuously without exceeding specified temperature rise
limits.
This setup enables one primary supply to serve the entire load in case
the other is unavailable.

Voltage Rating: The maximum voltage, whether AC or DC, at which the
fuse is designed to operate.

Transfer can be performed manually or automatically, with electrical
or mechanical interlocks used to prevent inadvertent connections
between the two sources.

Interrupting Rating: The maximum short-circuit current at rated
voltage that the fuse can safely interrupt.


The transformer section is responsible for transforming incoming
power from the higher primary voltage to the lower secondary
voltage.
Fuses should carry 110% of their rating continuously without
exceeding specified temperature limits.

Fuses should open within specified time frames when carrying 135%
to 150% of their rating in a test circuit.

Different current and voltage ratings of fuses should have specified
physical dimensions to prevent interchangeability.

Interrupter switches or air-filled terminal chambers may also serve
the application.

In primary-selective systems, two interrupter switches may serve a
common bus or two buses with an interrupter tie switch.


The transformer is mechanically and electrically coordinated with
both the incoming line (primary) section and the low-voltage
switchgear section.

The low-voltage switchgear section offers protection and control for
low-voltage feeder circuits.

Fuses listed as having interrupting ratings above 10,000 A should
display their interrupting rating on the fuse label.

It can be composed of various components, such as a drawout circuit
breaker switchgear assembly, a metal-enclosed distribution
switchboard, a panelboard mounted in or on the transformer section,
or a single secondary protective device.

Class H Fuses (0-600 A)

Class J Fuses (0-600 A)

Class K Fuses (0-600 A) - Class K1 and K5

Class R Fuses (0-600 A)

Most manufacturers use aluminum bus work as the standard, but
copper is also available at an additional cost.

Panelboards are classified into two main categories: lighting and
appliance panels, and power distribution panels.

Supplementary Fuses (Special characteristics for supplementary
overcurrent protection)

Lighting and appliance panels are used to distribute electrical power
to lighting fixtures and various appliances in commercial buildings.

Cable limiters are used in multiple-cable circuits to provide shortcircuit protection for cables.

Power distribution panels are used to distribute electrical power to
larger loads such as machinery, equipment, and HVAC systems.

They are rated based on cable


Panelboards for power distribution are designed to handle higher
electrical currents and are equipped with circuit breaker devices or
fuses capable of managing larger loads.
Cable limiters are devices that limit the extent of a fault in a cable
system while preserving service to the rest of the system.

Cable limiters do not provide overload protection.

Motor starter units may also be mounted on panelboards to control
and protect electric motors.

Low-voltage fuses are used for overload protection in low-voltage
systems.

NEMA PB11990 (Panelboards) is a relevant standard for panelboards
that provides specifications and requirements for their design,
construction, and safety.

Low-voltage fuses have high interrupting ratings.

A service protector is a non-automatic circuit-breaker-type switching
and protective device.

It includes an integral current-limiting fuse and can be operated
manually or electrically.

Service protectors are designed to handle currents up to at least 12
times their continuous current ratings.

They are capable of closing and latching against fault currents of up to
200,000 A symmetrical rms.

ANSI/UL 67-1988 (Panelboards) is another relevant standard for
panelboards that ensures they meet industry standards and safety
regulations.

Thermal Magnetic MCCBs offer inverse time-delayed tripping for
overloads and provide instantaneous tripping through coils or
magnet and armature designs.

Magnetic Only MCCBs are primarily used for instantaneous tripping in
specific applications such as welding or motor circuits.


Integrally Fused MCCBs incorporate current-limiting fuses within the
molded case, ensuring safe operation in systems with high shortcircuit current ratings.
Service protectors are capable of withstanding the stresses created by
the let-through current of the fuses during fault interruption.

Current Limiting MCCBs effectively reduce let-through current and
energy (I²t) using electromagnetic principles and are suitable for
systems with high fault currents.
Service protectors are suitable for switching and protection under
various conditions, including normal load, overload, and fault
switching up to their maximum interrupting capacity.

They provide protection against single-phasing, a condition where
one of the three phases in a three-phase system is affected.

Service protectors are mechanisms or tools that are used to ensure
the uninterrupted functioning and availability of a service.


High Interrupting Capacity MCCBs are designed for applications in
systems with high fault currents and use strong, high-temperature
materials.

Molded-Case Circuit Breakers can be used in individual enclosures,
panelboards and distribution switchboards, switchgear, combination
starters and motor control centers, and automatic transfer switches.

They are designed to detect and mitigate potential threats or
disruptions to the service, such as cyber attacks, hardware failures, or
natural disasters.

Types of fuses include non-time delay fuses, time delay fuses, and
dual-element time delay fuses.

Service protectors may include features such as redundancy, backup
systems, failover mechanisms, and monitoring systems.

Non-time delay fuses are used in circuits other than motor circuits or
in combination with circuit breakers.

Electrical trip switches have a contact interrupting rating of 12 times
their continuous rating.

Time delay fuses have intentional built-in time delays and are
commonly used for motor overcurrent protection.

Their primary goal is to maintain the reliability, performance, and
security of the service, even in the face of unexpected events or
challenges.

Service protectors are available in various continuous current ratings,
including 800 A, 1200 A, 1600 A, 2000 A, 3000 A, 4000 A, 5000 A, and
6000 A.

They are designed for use on both 240 Vac and 480 Vac systems.

Service protectors come in two- and three-pole construction.

They can be installed in wall-mounted and free-standing
compartments, as well as switchboards.

Service protectors are often used in conjunction with ground-fault
protective equipment.

Their circuit breaker-type construction allows for rapid fault clearing
in the event of a ground fault, typically achieving a total fault clearing
time of under 3 Hz after shunt tripping by the ground-fault detector.

Ground Fault: Switches used as disconnects in conjunction with
ground-fault detectors should be carefully coordinated with fuses to
ensure proper operation and protection.

Bolted Pressure Switches consist of movable blades and stationary
contacts with arcing contacts, featuring a simple toggle mechanism
and a spring for quick-make and quick-break switching action.

High-Pressure Contact Switches employ an over-center toggle
mechanism with high-energy springs, allowing for higher acceleration
when parting or closing contacts and resulting in a higher
interrupting capability.

Electrical trip mechanisms can be added to bolted pressure switches
and high-pressure contact switches for automatic electrical opening.

Electrical trip switches are designed for remote tripping or for use
with ground-fault protection equipment.

Electrical trip switches can trip at 55% of normal voltage and have an
opening time of approximately 6 Hz.

Both manually operated and electrical trip switches are designed for
use with Class L current-limiting fuses.

IEEE C37.29-1981 (Reaff. 1985), IEEE Standard for Low-Voltage AC
Power Circuit Protectors Used in Enclosures (ANSI), is the applicable
standard for service protectors.

Enclosed switches are switches that may or may not have fuse holders.

They are completely enclosed in a metal enclosure.

Trip switches are available in various current ratings, including 800 A,
1200 A, 1600 A, 2000 A, 2500 A, 3000 A, 4000 A, and 6000 A.

Enclosed switches are designed to be operable without opening the
enclosure.

Trip switches are rated for 600 Vac and can carry 100% of their rating.

They typically have provisions for padlocking in the off position.

Trip switches are suitable for use on circuits with available fault
currents of up to 200,000 A symmetrical rms.

Detailed requirements and standards for enclosed switches can be
found in NEMA KS1-1990 (Enclosed Switches) and ANSI/UL 98-1986
(Enclosed and Dead-Front Switches).

Trip switches can be mounted in switchboards or housed in
individual wall-mounted and free-standing enclosures.

Bolted pressure switches and high-pressure contact switches are
subject to standards such as ANSI/UL 977-1984 (Fused Power-Circuit
Devices) and CSA Std C22.2-1980 (Canadian Electrical Code, Part 2:
Safety Standards for Electrical Equipment, Electrical Signs).

Manufacturers' catalogs should be consulted for a complete range of
equipment features and specific application information.
General-Duty switches can interrupt up to 600% of full load current
50 times at rated voltage and can achieve interrupting ratings up to
200,000 A when used with specific fuse types.

These switches play a critical role in electrical distribution systems,
providing reliable switching and protection capabilities, especially in
applications where high interrupting capabilities are required.
Heavy-Duty (Type HD) switches are available in ratings from 30 to
1200 A and are intended for systems not exceeding 600 Vac (and
possibly 600 Vdc).

Network protectors prevent backfeeding from the collector bus to the
transformer or primary feeder during fault conditions or when
restoring power to a feeder.
Heavy-Duty switches accommodate Class H, J, L, or R fuses and
approved kits are available to convert them for use with different fuse
types.

Network protectors do not provide forward overcurrent protection,
but rely on fuses to open slowly under heavy short-circuit currents,
allowing faults in network cables to self-clear and downstream
overcurrent devices to operate.

Cable limiters are used in modern network protection systems to
isolate cable faults.

Network protectors have fuses that are primarily used to remove a
protector and transformer from the secondary bus in case of relay or
protector trip mechanism malfunctions.

Network protectors incorporate two plug-in relays: the master relay
and the phasing relay.

The relays trip the protector circuit breaker if power flows from the
collector to a transformer and reclose the circuit breaker when the
transformer secondary voltage is slightly above and leading the
collector bus voltage.

Relay settings involve complex considerations, including a 360°
vector diagram for power direction and magnitude settings to account
for voltage differences.

General-Duty (Type GD) switches are rated from 30 to 600 A and are
intended for light-duty applications where typical load conditions are
present.

General-Duty switches are designed for use in systems not exceeding
240 Vac and are compatible with Class H fuses.




Heavy-Duty switches have interrupting requirements based on their
equivalent horsepower (hp) ratings and should be able to interrupt
400% of full load current 50 times at rated voltage for switches
approved for use with DC motors.

UL categorizes switches into three categories: general use without an
hp rating, general use with an hp rating, and fuse motor circuit type.

UL specifies interrupting requirements for switches, such as
operating 50 times at 150% of nominal current for general-use
switches.

Horsepower-rated switches have requirements similar to NEMA for
ratings above 100 hp.

Ratings less than 100 hp should interrupt load currents 50 times at
approximately 160% of nominal current.

Current Rating: Select switches with a current rating of at least 125%
of the expected continuous load current.

Frequency: Most AC-rated switches are approved for 60 Hz systems
only unless otherwise specified.

Network protectors are withdrawable and may require special safety
precautions when removed from an energized circuit.

Temperature: NEMA and UL specify temperature limits, with a
maximum temperature rise of 30°C (86°F) throughout the conductor
path when operated without fuses and carrying rated current.

Some ratings of network protectors may require internal
disconnection by maintenance personnel for withdrawal.


Fused Switches: Enclosed switches with fuses are tested for their
capability to withstand let-through currents of the fuses or interrupt
currents that don't cause instantaneous fuse melting.
Network protectors can be equipped with external controls to trip
and lockout in response to various types of relaying, including
overcurrent, ground, or heat sensing relays.

Desensitizing relays may be used with network protectors to prevent
nuisance tripping, especially in scenarios involving regenerative loads.

Network protectors are available in various ratings and voltage levels,
including 125 V, 240 V, 480 V, or 575 V.

Maximum current ratings for network protectors can reach up to
5000 A.




Network protectors come in different enclosure types, such as
dustproof, dust-tight, dripproof, and submersible enclosures, allowing
for flexible placement within buildings.
Conventional network systems are optimally fed from "balanced
feeders" that are physically identical and dedicated to network
service. Using undedicated feeders requires special design
considerations.
Network protectors have limited overload capacity compared to the
transformers they are associated with, which typically have heavy
overload capabilities.
Protectors are usually rated with higher current capacities than the
transformer's full-load rating.

The choice of loads to be transferred depends on the importance of
the equipment and the allowable duration and frequency of
interruptions.

The reliability requirements for critical loads are classified into three
levels: Level 1, Level 2, and Level 3.

Examples of Level 2 critical loads include transportation systems and
critical controls for heating, ventilating, and cooling.

Examples of Level 3 critical loads include computer data processing
systems and manufacturing processes.

The choice of load transfer devices should be based on the required
reliability classification of the utilization equipment.

Consideration should be given to motor loads, ensuring that the
transfer device and standby power source can handle the load's
characteristics.

Load transfer devices should have the capability to make and break
load current, carry rated current continuously when closed, withstand
fault currents, and interrupt full load currents as per applicable
standards.

Overhead power lines have higher insulation levels compared to
terminal apparatus like transformers, switchgear, and potheads.

Overhead lines are susceptible to overvoltages caused by lightning
strikes and switching surges, which can vary in magnitude.

Accessibility and ease of inspection of contact elements are important
factors.

Traveling voltage waves tend to increase in voltage when they reach
equipment with a surge impedance higher than that of the incoming
line.

Automatic or manual transfer switches (up to 4000 A in low-voltage
and 1200 A in medium-voltage class).


Incoming waves can approximately double in magnitude at the
terminals of transformers or open circuit breakers, leading to
overvoltage risks.
Automatic power circuit breakers (600–3000 A, low- and mediumvoltage).

Manually or electrically operated bolted pressure switches (600 V,
800–6000 A).
Examples of Level 1 critical loads include health care facilities, egress
lighting, fire detection, and military systems.

Static transfer switches for special applications, such as UPS systems.

Automatic transfer switches are used primarily for emergency and
standby power generation systems.

They should be mechanically held and electrically operated to meet
code and standard requirements for reliability.

Special consideration should be given to their ability to handle high
inrush currents, carry full rated current, withstand fault currents, and
interrupt full load currents.


Outdoor substation installations often employ grounded masts or
overhead ground wires to intercept lightning strokes and protect
power lines and equipment.

Surge arresters and capacitors are used to limit overvoltages and
attenuate excess energy during transients caused by events like
lightning strikes, heavy current switching, and system faults.

Surge capacitors act as a short circuit to high-frequency transients.

Gapless-metal-oxide surge protectors are commonly used for high
transient overvoltages.

Circuit breakers may or may not require an energy source like an
electric storage battery for operation.

Equipment like solid-state electronic equipment, motors, and drytype transformers are susceptible to overvoltages and may require
protection.

Magnetically operated transfer switches and solenoid-operated
circuit breakers are rapid in operation.

Motor-operated circuit breakers are slower.

Surge arresters come in three types: station, intermediate, and
distribution, with varying abilities to handle surge energy.

These devices operate rapidly (typically less than 0.5 seconds) and
require special consideration for motor loads.
Selection of arrester protection depends on factors like insulation
levels, arrester characteristics, exposure to lightning, and surges.

Measures may be needed to prevent phase differentials in motor
loads upon transfer.

Accessories like time delays, in-phase monitors, and controls to
disconnect and reconnect motors may be used.

Additional accessories include time delays, test switches, auxiliary
contacts, remote annunciators, lockout relays, and switching neutral
contacts as needed.

Bypass isolation switches allow the isolation of the transfer switch for
maintenance.

Transfer devices can be unidirectional or bidirectional with manual
reset from emergency to normal positions.

Time delays and controls ensure proper timing of transfer operations.

Consideration should be given to the interruption of equipment
during a transfer operation and the need for automatic or manual
restart.

Switching of the neutral conductor may be necessary to properly
ground the service source and alternate sources and simplify groundfault sensing.

Positive Mechanical Interlocks involve physical connections or
mechanisms that prevent the simultaneous operation of two devices.


Electronic systems, including computers and communication systems,
are sensitive to EMI from power supplies, interconnecting cables, and
radiated electric and magnetic fields.

Strategies for reducing EMI include specifying equipment with
controlled emission levels, using filtering and noise suppression
techniques, and employing optoelectronic isolation and fiber optics
for sensitive circuits.

Techniques for control and communication wiring include metallic
conduit, shielding, twisted pairs, and effective grounding.

Equipment like isolation transformers, motor-generator sets, power
conditioners, and uninterruptible power supplies (UPS) can help
mitigate the effects of poor-quality power, including transients,
harmonics, dips, and voltage regulation issues.


Various standards and guides, such as NEMA LA1-1986, IEEE C62.11989, IEEE C62.2-1987, and IEEE Std 518-1982, provide guidance on
surge protection, noise reduction, and minimizing electrical noise
inputs to controllers.
Load transfer devices are essential to ensure continuity of power for
critical loads in commercial buildings.








Key Interlocks use keys to enforce staged or controlled operations of
equipment or access control.
Examples of Key Interlock Applications include preventing the
simultaneous closing of two feeds in a double-ended substation,
preventing the opening of a screen or door in front of a mediumvoltage fuse unless the associated interrupter switch is open, and
preventing the closing of a feeder service.
Key interlock assemblies can be designed to require the insertion and
removal of several keys into a multiple-lock assembly block before
any action can be taken, ensuring multiple conditions or steps are met
before a specific operation is allowed.
Proper control and management of keys are essential in key interlock
systems to maintain safety and prevent unauthorized access or
operations.
Duplicate keys in the hands of operators pose a safety hazard and
should be avoided.
Nominal Ratings: All power equipment is assigned nominal ratings for
voltage, current, phases, and frequency, representing the conditions
at which the equipment is designed to operate.
Ambient Conditions: The conditions of application, such as ambient
temperature and altitude, can affect equipment ratings, and
manufacturers' data and standards provide information about these
limits and any necessary de-rating or uprating considerations.
De-Rating: De-rating is the practice of reducing equipment's nominal
rating to account for non-standard conditions, with the NEC and other
standards specifying de-rating values for certain equipment types
when operated under conditions other than normal.

Full voltage starting is common for applications like ventilating fans
or small pumps.

Larger motors may cause voltage dips, affecting the lighting system.

Electric utilities have restrictions on starting currents to limit voltage
fluctuations.

It is essential to check starting limitations with the utility and
consider using reduced voltage starters before applying large motors.

Time settings for overload relay should be longer than part-winding
starters.

Motors are primarily associated with controllers and are used in
heating, ventilating, air conditioning, refrigeration, pumping,
elevators, and conveyors.

Standardized ratings for medium-voltage starters range from 25007200 V, and for fused Class E2 controllers range from 160-570 MVA.

Controllers can be operated manually or automatically.

Part-winding starters reduce inrush current and torque by 65% and
42% respectively by connecting part of the winding to supply lines
and balancing, typically with two equal windings.

Part-winding starters have a starting time of 2-4 seconds and require
branch-circuit protection at 200% of each winding current. They are
suitable for light loads such as high-speed fans or compressors.

Resistor or reactor starters are the most basic reduced voltage
starting method, using a primary reactor or resistor to reduce voltage
across motor terminals and inrush current.

After a predetermined acceleration period, a timer closes a second
contactor to short the primary resistor and connect the motor to full
line voltage, ensuring a smooth transition from starting to running.

The impressed voltage on a motor is influenced by its speed.

The starting torque of a motor is determined by the square of the
applied voltage.

Resistor- and reactor-type reduced voltage starters offer closed
transitions for standard motors, with resistors typically selected for 5
seconds on and 75 seconds off.

Resistor-type starters have better torque speed characteristics but
are less expensive and are used more frequently.

Resistor-type starters are difficult to adjust and are typically used for
larger medium voltage motors.

Fault-Make Rating: The ability of equipment to safely close on a fault.

Short-Time Rating: The ability of equipment to withstand overcurrent
for a limited time.

Interrupting Rating: The ability of equipment to clear fault currents
safely.

Open vs. Enclosed Ratings: Equipment ratings may differ based on
whether the equipment is installed in enclosures or used in the open.

Temperature Considerations: Equipment terminals, particularly in
low-voltage applications, may have temperature ratings that need to
be considered when connecting cables.

Power, distribution, and general-purpose transformers can withstand
short-term overloads that are twice their normal rating.

Circuit breakers and fuses are typically limited to smaller overloads,
such as 10%.


Medium-voltage equipment requires insulation coordination to
ensure proper surge protection and system protection under surge
conditions.
Autotransformer starters are more efficient than resistor reactor
starters due to their ability to reduce voltage by transformation.

Insulation coordination involves studying BIL (Basic Impulse
Insulation Level) ratings and applying surge protection measures as
needed.
The starting torque of a motor is directly proportional to line current,
as the magnetizing current of the autotransformers usually does not
exceed 25% of the full-load motor current.

Autotransformer starters have taps for 65% and 80% voltage for
motors up to 50 hp and 50%, 65%, and 80% voltage for larger motors.
CHAPTER 6: Motor Controllers and Starting
Methods

The torque remains constant until the transfer from starting to
running voltage in autotransformer starters.

In closed transition, contactor 2S is smaller.


An overload relay is included in wye-delta starters, set at 58% of the
full-load motor current.
The "Korndorfer connection" is commonly used with autotransformer
starters to overcome the issue of constant torque during voltage
transfer.


Controllers are crucial in commercial buildings and are used to
control heating, lighting, ventilation, air conditioning, elevators, and
more.
Wye-delta starters carry 58% of the motor load, with contactors 1M
and 2M carrying 33.3%.

Wye-delta starters have a higher NEMA rating than full voltage
starters.
The National Electrical Manufacturers Association (NEMA) publishes
standardized ratings for controllers, ranging from 2 hp to 1600 hp.

Open transition starters, especially for autotransformer starters,
require careful selection of branch-circuit protection.

Wye-delta starters are commonly used in Europe and the US for large
air-conditioning units.



Most integral horsepower motors in commercial buildings are
squirrel-cage designs and powered by three-phase, AC, low-voltage
distribution systems.

A motor controller is a device that starts, stops, and protects a motor
connected to it.

Series-parallel starters connect two windings in series, allowing
maximum impedance, inrush current, and torque.

It uses a magnetically operated contactor to connect the motor to the
power source.

Solid-state starters provide a smooth, stepless method of acceleration
for standard squirrel-cage motors.

Each device should be tested and approved separately, except for
fusible switches with 5000 A or less short-circuit current for size 1
and 2 starters.

Combination starters consist of a disconnect device, pilot device,
starter, and control transformer, all mounted on a wall or machine.

They must be approved for short-circuit current and can withstand up
to 100 kA at 480 V.

Modular combination starters with multiple width and length
dimensions are used in simplified control centers, placed in front of a
steel structure and wired to a bus system.
Motor branch circuit protection is divided into running overload and
short-circuit protection.

Complex panels, placed in large enclosures, have group protection
and are used for controlling large machines or production lines.

Running overloads are up to locked-rotor current, usually six times or
eight to ten times the full-load motor current.

Motor control centers are essential for central control of multiple
motors and consist of basic vertical structures with a vertical and
horizontal bus system.

NEMA Standards have recommended three overload relays for
running overload protection since 1972.

Vertical sections of motor control centers have prefabricated units
that can be plugged into the bus structure.

The total width of each vertical section is not standardized, but most
manufacturers use a basic width of 20 inches.

Three methods of acceleration available for solid-state starters are
constant current acceleration, current ramp acceleration, and linear
timed acceleration.

A tachometer feedback circuit is needed for acceleration.

A solid-state control circuit manages silicon controlled rectifiers.

Contactors provide isolation between the motor and load.

Solid-state starters are suitable for fast or large operations and are
used for speed control of AC and DC motors.


Overload relays are divided into three classes: Class 30, 20, and 10.

Class 20 overload relays are used for T-frame motors, while Class 30
is used for older U-frame motors.

Leveling channels may be installed to ensure proper alignment.

Ambient compensated and non-compensated overload relays are
available for various applications.

When selecting motor control centers, it's important to consider the
placement of incoming and outgoing conduits.
IEC-type overload relays provide single-phase protection for threephase motors without one phase.

Conduits can be run horizontally on a ceiling or elevated structure,
elbowed or bent downwards to enter the top of the centers.

Removable top plates are typically provided for convenient conduit
entrances.


Short-circuit protection for the total motor branch circuit is provided
by short-circuit protective devices (SCPD), which can be a fuse or
circuit breaker.

Protection of starters should also be considered as required by
ANSI/NFPA 70-1990, National Electrical Code (NEC).

In some cases, conduits may be run horizontally into an upper section
of the centers, requiring a box-like metal structure.

Inherent motor protection is obtained with thermistors, which change
resistance at the switching point and de-energize the motor contactor.

In some cases, conduits may be embedded in floors, necessitating a
waterproofed trench below the centers.

Undervoltage protection allows motors to restart when normal
voltage is restored, while time delay undervoltage protection
prevents motors from being disconnected.

Metering, such as voltmeters, ammeters, kilowatt meters, power
factor meters, and running time meters, should be installed in motor
control centers.

Solid-state overload relays have been developed for special motor
branch circuit protection applications, combining current sensing,
transformation, rectifying, and feeding to an analog unit or
microprocessor.

There are no current standards for the number or types of meters in
motor control centers.

Identification labels should be provided for each motor starter,
devices, and compartments in motor control centers.

Additional floor space should be allocated for anticipated growth or
maintenance in motor control centers.

These devices can react to motor overload, phase loss, phase reversal,
mechanical jam, ground fault, current unbalance, voltage unbalance,
low-voltage conditions, and more.

Interlocking devices on compressors, vanes, dampers, and valves can
ensure the motor doesn't start if the load exceeds the available torque.

Frequent product redesign can render equipment obsolete, affecting
equipment availability in motor control centers.

Elaborate interlocking between motor controllers can ensure proper
sequencing in conveying systems.

Spare parts, such as starters and circuit breakers, should be provided
for periodic replacement.

Mechanically held contactors can perform additional functions like
motor feeder disconnect and controlling loads.

Spare fuses should be included for protective devices.


Combinations of switches, relays, and contactors can alternate the
operation of multiple-pump motors to equalize running time and
provide sufficient capacity for maximum load conditions.
Lockout tags/padlocks should be provided for safe disconnection and
service.

Enclosure types should be specified based on location and service,
with NEMA defining different types for indoor and dust-free areas.

Buses should be specified as either copper or aluminum.

The proper conductor terminating or connecting devices should also
be specified.

Enclosures should be designed to ensure safety and efficiency in the
operation of motor control centers.

NEMA classifies motor control centers as Class 1 or Class 2 assemblies.

Class 1 motor control centers are independent units with mechanical
groupings of motor control units, feeder-tap units, and other electrical
devices.

Class 2 motor control centers are interconnected units with
manufacturer furnished electrical interlocking and wiring between
units.



There are different arrangements available for control systems in
commercial buildings, with the physical configuration varying
depending on the complexity of the system.
Panelboard-type constructions involve placing the fusible disconnect
or circuit breaker for each branch circuit in one enclosure, with the
handle attached to the door or disconnect device.
The starter, control transformer, pushbuttons, and pilot devices are
placed in other enclosures, interlocked to only be accessible when the
disconnect device is off.

The disconnect device is usually connected to the bus bar system of a
switch-type panelboard.

Separate enclosures can be used for disconnect devices and starters,
connected by conduit or cable.

Class 1-S and 2-S motor control centers have custom drawing
requirements and special identifications for electrical devices,
terminal numbering designations, and sizes of drawings.

The most common controller is the across-the-line magnetic-type
starter, which uses an electromagnet to close contactor contacts.

The control voltage is typically 120 V, but other voltages can be used.

Using parallel or sliding-type contacts is recommended for low
control voltage to avoid continuity issues and the need for larger
wires.

120 V is the most common control voltage due to greater insulation
integrity and personnel safety precautions required for high control
voltage.

Overload relays are placed on the load side of contactors to provide
overload protection in each phase.

Overload relays can be nonambient or ambient compensated and
have separate indicating contacts for tripping.

Overload relays should be trip-free and reset manually, with
automatic reset not acceptable on machines where automatic
restarting of the motor could be hazardous.

NEMA standardized starters and contactors have three classes of
overload relays.

Overload relays should trip at 125% full-load current for 40 °C rise
motors and 115% full-load motor current for all other motors.

NEMA-rated controllers provide high performance over a wide set of
application conditions.



IEC-type controllers are rated based on laboratory performance and
are typically smaller and provide lower performance than NEMA-type
devices.
NEMA-type controllers are preferred for their longer life, higher
short-circuit withstand capability, replaceable contacts, and broad
application capability.
NEMA-type controllers are suitable when motor service factor, duty
cycle, contactor life requirement, or short-circuit protective device
are unknown or terminal markings may cause problems.

Defined-purpose contactors are used for specific applications, such as
resistance heating, crop drying equipment, and commercial deep-fat
fryers.

Manually operated controllers are limited to size 1 maximum and
have a longer life than circuit breakers due to their frequent switching
of rated motor currents.

Solid-state contactors are crucial for high-volume operations and high
shock/vibration resistance. With decreasing costs, their market share
will increase, making them competitive for adjustable frequency
drives and reduced voltage starting applications.

Fire pump controllers provide limited overcurrent protection and
short-circuit protection.

The standard for fire pump controllers is ANSI/NFPA 20-1990,
Installation for Centrifugal Fire Pumps.

Fire pump controllers can provide manual or combined manual and
automatic operation, with the manual-only type rarely installed.

Power for fire pump controllers is usually obtained from a tap or a
separate service.

Fire pump controllers are typically wired to the power source near
the service entrance or provided with a separate service.

ANSI/NFPA 20-1990 mandates that fire pump controllers have a
withstand rating equal to the maximum short-circuit current that can
flow to the controller.

Medium-voltage starters and controllers are suitable for larger
motors in commercial buildings.

Medium-voltage starters and controllers offer lower currents and
minimal line disturbance.

Class E1 and Class E2 controllers function similarly to low-voltage
controllers and are available in various configurations and contactor
types.

Motor disconnecting is achieved using disconnecting switches or
multiple-disconnecting-type fuses.

120V control circuits are supplied through transformers.

Medium-voltage controllers can withstand high basic impulse
insulation levels.

Synchronous motor starters bring the motor to synchronous speed
with the dc field de-energized and energized near synchronism.

Small induction motors can be mounted on the shaft for speed.

Most synchronous motors are polyphase and can be started as
squirrel-cage induction motors.

Starting methods for synchronous motors include starting resistance,
reactance, and combinations of these.

DC motors can start with full voltage or reduced voltage methods,
with reduced voltage starting involving a series resistance.

Speed control for DC motors is achieved by varying resistance in
fields or armature circuits.

Solid-state DC motor drives are increasingly used for adjustable speed
applications.

There are manual and automatic pilot devices that initiate the control
of motors.

Manually operated devices include pushbuttons, selector switches,
and master switches.

Selector switches open and close coil circuits and connect to
automatic switches.

Magnetic motor starters can be connected to multiple-speed motors
to achieve different motor velocities.

The windings of each phase can be connected in two ways, resulting
in a stator winding with half the poles in one position.

Pushbuttons can change circuit states only as long as pushed.

Two-speed motors can operate at equal power, equal torque, or
variable torque.

Standardized pushbutton lines include standard duty, heavy duty, and
oil-tight.
It is important to disconnect the high-speed winding to prevent high
torque and overcurrent.

Operators include mushroom-head buttons, key-operated switches,
handles, and pilot lights.
Two-speed motors with different speed ratios should have separate
windings.

Automatically operated devices switch a coil circuit based on the
actuating medium.
Motors with three and four speeds can be created by combining these
elements and using controllers.

Conventional limit switches convert mechanical motion into electrical
control signals.
Pole amplitude modification (PAM) motors are available for arbitrary
speed ratios, using conventional two-speed motor controllers.

Proximity limit switches operate when an object approaches a sensor.





Fire pump controllers are essential in commercial buildings to
maintain water pressure during fires.

Float switches, pressure switches, sail switches, and temperature
switches are examples of automatically operated devices.

They are typically driven by electric motors or diesel engines,
depending on reliability and environmental conditions.

Logic diagrams can be developed using electromechanical relays,
mechanically held relays, and timing relays.

Timers can be motor-driven, dashpot, thermal, solid-state, or
pneumatic.

Legal requirements for services to meet construction standards exist
in many states, often following utility and safety codes.

Programmable controllers are microcomputer-based, solid-state
devices that use digital logic and can be easily reprogrammed.

Overhead service laterals are commonly terminated at brackets on
small buildings for electrical service.

They can add functions difficult to obtain with standard relays and are
generally less expensive than relays.

Larger buildings may be served by open-wire lines connected to
external transformer substations or cable terminal poles.

The central processing unit (CPU) checks the control plan stored in
memory, which can be read-only, read and write, or random access.

Aerial cable supported by grounded messengers is another option for
supplying electrical service to buildings.

Programmable controllers can be studied and checked on computer
terminals, and can also be used as input sources for electromechanical
control devices.

The passage discusses the materials and construction methods used
for open-wire lines, including conductor types and support structures.

Compliance with voltage and insulation requirements is essential for
overhead service design.

Acceptance by the utility provider is a crucial factor in the design
process for overhead service.

Safety measures include maintaining clearances from buildings,
railroad tracks, and driveways, providing adequate climbing and
working space for personnel, and assessing mechanical strength
based on factors like wind and ice loads, pole diameter, and wire size
and strength.

Speed control of DC motors involves regulating armature or field
current, with torque inversely proportional to field strength and
counter-electromotive force.

The counter-electromotive force (CEMF) is equal to the applied
armature voltage (V) minus the armature current (I) times the
armature resistance.

The speed of a shunt motor can be increased by changing the field
strength, adding resistance to the field circuit, or by switching a
resistor into the isolated armature circuit.

The NESC classifies safety levels into construction grades B, C, and N,
with Grade B being the strongest.
The speed of series motors can be regulated by adding resistors in the
armature and field circuit or parallel to the armature to DC.

Insulation measures involve protecting against lightning surges using
surge arresters, shield wires, and enhanced insulation, as well as
safeguarding against voltage surges caused by power switching.
Grounding systems help dissipate lightning currents and minimize
damage.

Safety near traffic areas or buildings is important.

Medium-voltage services have different considerations compared to
low-voltage services.

Installing open-wire electrical lines over or near buildings can
interfere with firefighting and maintenance operations.

Fully insulated cables are recommended as a safer alternative,
especially for medium-voltage applications.

Cables attached to a building's exterior should be enclosed in
grounded metallic conduits, and if on flammable surfaces, encased in
concrete.


DC motor control has evolved over time, with phase control of siliconcontrolled rectifier (SCR) converters being the main method.

Full wave bridge-type rectification is used for single-phase AC, while
three-phase AC uses three SCRs or six SCRs and three diodes.

Motor reverse can be achieved by reversing the polarity of the field
windings, armature voltage, SCR converters, or generator field voltage
in a motor-generator system.

AC induction motors' speed depends on synchronous speed, pole
number, and slip.

Supply frequency controls synchronous speed, while slip depends on
voltage and current regulation.

Wound-rotor motors offer stepless speed control due to adjustable
secondary resistance.

AC adjustable frequency drives offer energy savings and a wide range
of speed and torque control.

Safety clearances for personnel must be maintained when open wire
is used over buildings, following NESC provisions or local code rules.

Common types include variable voltage input (VVI) and pulse width
modulated (PWM).

"Tree" coverings should not be relied upon for insulation on overhead
conductors above 2000 V to ground; proper insulation and shielding
are necessary.

AC-dc-ac controls control frequency and voltage, allowing braking and
reversal.

Bare conductors must be protected in line with regulatory
requirements.
These controls are used with both induction and synchronous motors,
providing wide speed ranges.

Safety and compliance with regulations are paramount in outdoor
electrical installations.

Designing outdoor structures, such as overhead electric lines, should
factor in weather forces like wind and ice loads.


Cycloconverter drives are an economical alternative to dc link drives,
synthesizing adjustable frequency and voltage AC output directly
from input waveforms, suitable for low speeds.

Adjustable speed motor controls use solid-state techniques to create
nonsinusoidal, square-edged AC input current waveforms.

Location-specific considerations are essential, as weather severity
varies across the United States.

These currents may contain harmonic frequency components, which
can cause damage to the power system.

In areas with damp or polluted atmospheres, special insulators with
extended leakage distances or resistance grounded insulators may be
needed to prevent contamination-related issues.

These harmonics can be eliminated by changing a capacitor bank
rating, and electrical consultants and equipment suppliers can
provide advice on preventing or curing these issues.

This approach ensures the reliability of outdoor electrical structures.

Underground construction may be necessary in various situations,
including conflicts with overhead structures, high load density, local
regulations in new residential areas, and aesthetic considerations.

Underground systems offer advantages over overhead systems, such
as improved aesthetics and fewer issues.

Underground systems, particularly those involving conduits and
manholes, are generally more costly than overhead systems.

Direct-burial-type systems like URD and CIPUD can significantly
reduce costs for new developments compared to conduit-andmanhole systems.
CHAPTER 7: Overhead Service



Incoming electric lines and service laterals connect a building to the
utility's power source.
Clearance conflicts with existing or future structures should be
avoided when planning these connections.
Factors like voltage, ownership, maintenance, and installation costs
can vary by region.




Underground construction is necessary under certain conditions, such
as conflicts with overhead structures, high load density, local
ordinances, or aesthetics in residential subdivisions.
Underground systems offer benefits like fewer issues compared to
overhead systems, but they come with higher repair costs and initial
expenses.
Direct-burial-type systems like URD (Underground Residential
Distribution) and CIPUD (Commercial and Industrial Park
Underground Distribution) are cost-effective options for new
developments.
URD is a single-phase distribution system for residential areas, using
organic insulated and jacketed cables with pad-mounted transformers
or prefabricated installations.

CIPUD is a three-phase system for commercial/industrial park
distribution, using looped cable systems with pad-mounted
transformers or above-ground switchgear.

Fault indicators aid in rapid fault detection and repair.

Maintenance and operation of these systems should be managed by
utilities or trained personnel due to their direct burial nature and
limited load handling capability.

Passing service entrance conductors through buildings poses a safety
hazard.

The circuit inside the building is typically not protected against short
circuits, overloads, or arcing faults.

Short distances for these circuits are considered safer.

Longer circuits should be enclosed in a raceway encased in at least 2
inches of concrete or metallic conduit encased in concrete to enhance
safety.




Encasing service entrance conductors in concrete within the building
is a recommended practice to enhance property and life safety.
Busways, neutral grounds, overheat detectors, and cable limiters are
discussed as methods and materials to protect against faults and
ensure service continuity.

The availability of multiple system voltages from the utility can lead
to the provision of different voltages for various building functions.

The physical characteristics of the building, such as size and distances
between buildings within a facility, may require multiple services.

Compliance with NEC and local code requirements, including
considerations like fire walls, can impact service design.

Provisions for future load capacity should be included in the initial
design, with service capacity typically exceeding immediate needs.

Service equipment design should allow for the addition of protective
devices for future feeder expansions.

The physical arrangement of the service entrance can vary based on
the utility's distribution system and the building's type.

Options for the physical arrangement include transformer vaults
located outside the building with bus stabs through the basement wall,
transformer vaults inside the building (in the basement or on upper
floors), underground services, and overhead services.

Engineers should check for high short-circuit current from
transformers with low impedance.

Service entrance equipment rooms should be easily accessible, welllit, dry, and compliant with electric utility and local code
requirements.

Plans should consider future equipment replacement and provisions
for smoke exhaust in the event of an electrical fire.

Service entrance equipment is important for supplying a building's
electrical load.

It should be designed to meet future demands or easily upgraded.

Collaboration between the building's engineer and the utility is
crucial for optimal equipment and voltage selection.

Planning should consider both current and future needs and happen
early in the process.

The engineer should provide necessary data to the utility.

Compliance with NEC requirements, state laws, and local ordinances
is essential for service entrance conductor installations within
buildings.
Details like service type, voltage, and overhead/underground options
must be decided.

Proper routing of cable systems, avoiding high ambient temperatures
and chemical exposure, is emphasized, with precautions for different
cable types.
Some utilities offer medium-voltage services, which require careful
planning but offer flexibility and cost savings for both the facility and
utility.

Detailed load characteristics, including kilovoltampere demand,
service continuity requirements, voltage specifications, special loads,
carrier current needs, largest motor inrush current, and power factor
considerations.

Comprehensive utility service details, encompassing available
voltages, billing demand clauses, rate structures, and potential need
for equipment modifications.

Physical and mechanical service entrance requirements, such as
service termination points, metering equipment locations, access
provisions, structural interference avoidance, and equipment
construction standards.

Electrical service requirements, including equipment voltage, BIL
levels, surge protection coordination, system capacity, fault capability,
protective device coordination, utility-approved equipment types, and
grounding methods.

Recommendations for manholes, pull boxes, and spare ducts in long
duct runs are provided to facilitate cable installation, maintenance,
and future expansion.

Precautions against laying duct systems in the same trench as gas or
sewer service are highlighted.

Service entrance conductors connect a client's service equipment to
the utility's service drop or lateral.

Service equipment includes main service control or disconnect, circuit
breakers, switches, fuses, and metering equipment.

The client typically owns and pays for service entrance conductors
and service equipment.

Billing metering instruments are typically owned and maintained by
the utility.

Schedule data, indicating important deadlines for service, load
requirements, and temporary construction service needs.
The design of service entrance equipment should ensure a highquality electric service without affecting other customers.

Medium-voltage system design flexibility, allowing control over
distribution systems, unit substation installation, and transformer
selection.

Low-voltage equipment design is categorized into three groups based
on capacity: Low-Capacity Circuits, which have current ratings under
600 A and are typically fed by individual transformers.

When multiple services come from one transformer bank, shortcircuit duty may range from 15,000 to 100,000 A.

Equipment choices are broad when available fault current is less than
10,000 A, and ground-fault protection is optional for lower current
installations.


Engineers must strike a balance between client needs and utility
requirements when designing service entrance equipment.

Service reliability requirements and power source influence the need
for multiple services or standby service with load transfer
arrangements.

Economic factors may impact service availability considerations.

The total load magnitude may necessitate additional services as
individual service capacity is limited by the utility.

Screening should prevent pests from entering, and fire-resistant
construction, like reinforced concrete, is ideal.

Vaults should have UL-approved 3-hour fire doors, sumps for spill
containment, and sealed floors.

Gratings should meet load requirements.

Multiple transformer banks should be in separate compartments for
safety, with associated switchgear enclosed.

Compliance with local codes, NEC, insurance, and utility rules is vital.

Pad-mounted three-phase transformers and switching equipment are
cost-effective and safe for various applications.

They are designed for surface pad installation, with no exposed
energized parts.

Additional enclosures can be added for specific needs or aesthetics.
Adding reactance to cable circuits connecting transformers to a
common bus or from each transformer bus to separate service
entrance circuit breakers or switches.

Posts should be installed in accessible areas to protect against traffic.

Vaults should allow for crane-based unit insertion and removal.

Installing reactors in the main service connection to reduce fault
current to the rating of the service entrance main and feeder circuit
breakers or switches.

Concealment options like landscaping or architectural fencing can be
used, considering utility operation and maintenance space.


Reactors can reduce fault currents to about 60,000 A.
Outdoor substations, except for pad-mounted equipment meeting
NESC Article 380 requirements, should be enclosed by walls or fences
with adequate aisles for safe operation and maintenance.

Current-Limiting Busway: Using current-limiting busway to reduce
very large short-circuit currents from 200,000 A to around 100,000 A.

Proper clearances, grounding, high-voltage warning signs, and locking
mechanisms are essential safety measures for substations.

Indoor substations, whether metal-clad or enclosed, require separate
enclosures or locked rooms for authorized personnel only.

Vaults should have multiple emergency escape routes with hinged
doors and panic bars for quick evacuation.

In large modern metropolitan office or commercial high-rise buildings,
multiple transformers are installed to meet high electric demands.



Medium-Capacity Circuits: These circuits have short-circuit duties
ranging from 50,000 to 100,000 A, with the actual fault current
determined by the utility.
High-Capacity Circuits: These service entrances have a short-circuit
capability exceeding 65,000 A, typically found in buildings fed from ac
secondary networks or large buildings with multiple parallel
transformers.
Engineers must examine the limiting characteristics of devices used in
medium and high-capacity circuits to ensure downstream protection,
and additional current-limiting devices may be necessary.

Dividing the electric circuits into independent parts, each fed by one
three-phase transformer or a group of transformers.

Using smaller service disconnecting switches or circuit breakers
equipped with current-limiting fuses to collectively handle the
available short-circuit current.


Current-limiting busway is effective when local codes permit
installing service entrance equipment at a distance from the building
entrance.

Current Limiting by Cables: Achieving current-limiting effects using
cables with controlled phase spacing, installed in nonmetallic
conduits buried in concrete.

Separating cables for each phase in three equally spaced nonmetallic
conduits to provide current-limiting reactance.


Current-limiting fuses start limiting current at 20-30 times their
rating and interrupt the circuit before it reaches its peak value on the
first half-cycle.
These transformers are connected to a common low-voltage bus
through a network protector.

Buildings have multiple points of power supply, such as beneath the
sidewalk, within the building, or on the roof.
The peak let-through current depends on the continuous rating of the
fuse and the available fault current.

The design of network installations involves determining utilization
voltage, the number of transformers, and service points while
adhering to regulations and economic considerations.

A crucial aspect of network design is ensuring the ability to install,
maintain, or replace components without disrupting service.

Network systems are designed to meet power demands on a
contingency basis, maintaining full-load capability even with a
predetermined number of components out of service.

First contingency networks typically use two or three primary feeders,
while second contingency networks may use more primary feeders.

The NEC specifies the minimum clear working space in front of
electrical equipment.

A second contingency network can maintain full-load capability with
two sets of components out of service, while a first contingency
network can maintain full-load capability with only one set of
components out of service.

Contingency design considers the entire distribution system, from
primary feeders to substations and switching stations, to ensure
seamless operation in case of component failure or damage.

The initial step in planning a network installation is creating a simple
sketch of the proposed setup using a standard vault equipment
arrangement.


Using larger current-limiting fuses with the service entrance switch or
circuit breaker can protect service equipment.

Smaller downstream current-limiting fuses or other methods, such as
current-limiting busway, cable runs, or reactors, can protect lowerrated equipment beyond the service entrance.

The NEC, Article 230–95, covers ground-fault protection
requirements for equipment.

Arcing ground faults can cause extensive destruction of equipment,
especially on high-capacity 480Y/277 V circuits.

Fully coordinated ground-fault protection schemes are recommended
for such systems.

Achieving proper ground-fault coordination may require a
combination of fixed time delay, inverse time delay, and zoneselective interlocking.

The design engineer should check the effectiveness of coordination in
all cases between the main service and feeder overcurrent protective
devices, as well as between the feeder and subfeeder overcurrent
protective device.

Equipment vaults housing service transformers require effective
ventilation to dissipate heat.

Natural ventilation is preferred, with a minimum of 3 square inches of
net ventilator area per kVA of transformer capacity.

The sketch should consider adaptations required in the building
structure and potential obstructions beneath the sidewalk.

Additional ventilation may be needed based on local codes and
climate conditions.

The design should ensure adequate space is available near customer
load centers.

Vertical ventilating shafts may require larger vent areas, fans, and
proper controls.

Subsurface conditions should be favorable to avoid costly pilings or
footings.

Environmental factors, such as water, should not pose significant
challenges.

Special attention should be given to the space and clearance
requirements of busway equipment.

Underground transformers can utilize natural convection cooling.

Adequate illumination should be provided for all areas in accordance
with the NEC, NESC, and ANSI/IES RP7-1983.

Exterior transformers may have corrosion-resistant finishes.


Interior transformers may employ ventilated-dry-type designs with
natural and forced air cooling options.
Ventilation should be provided to limit the ambient temperature of
the room to 40 °C (104 °F).


Compliance with municipal regulations, including considerations for
general structural design to support sidewalk loads or highway loads.
When a transformer other than a signal-type transformer is installed
in an electrical closet or room, some local codes require that a system
of mechanical ventilation be provided.

Specification of the location and size of ventilation and access panels.


Adequate ventilation is necessary for network installations with
vaults, typically requiring a minimum of 3 square inches of net open
area per 1 kVA of transformer capacity.
Electrical rooms and closets should only be used for electrical
equipment and maintenance, with no storage or non-electrical
utilities allowed to pass through.

Proper sealing of cable and busway openings is essential to prevent
issues like condensation, and fire stops should be in place where
needed.

Using these spaces for other purposes risks accidents and
unauthorized access.

Forced ventilation may be necessary, usually at a rate of 3 cubic feet
per minute per kVA, as per local codes or utility requirements.

Vaults should be constructed from reinforced concrete for strength
and explosion containment.

Vaults should be as watertight as possible, with provisions for
drainage.

Concrete floors should be sealed to prevent dust from entering
equipment.
CHAPTER 8: Cable System and Conductor Types

Factors to consider in cable system design include load current,
emergency overloading requirements, fault clearing time, voltage
drop, ambient temperatures, circuit length, and system frequency.

The ratio of vault volume to net ventilation area should be kept small,
typically less than 50 cubic feet per square foot of open ventilation
area, often around 30 cubic feet per cubic foot, to prevent excessive
pressure during secondary explosions.
The primary function of cables is to carry energy reliably between
source and utilization equipment.

Cables may be installed in raceway, cable trays, underground in duct
or direct buried, messenger supported, in cable bus, or as open runs
of cable.

Vaults must provide direct and rapid access for maintenance and
emergency personnel.

Cable systems can be classified into solid insulations, taped
insulations, and special-purpose insulations.

Suitable access routes should be included for transformer
replacement, which may involve removable slabs or walls.


Isolation or protective relaying may mitigate equipment failures, such
as explosions, fires, and smoke generation.
Cables with different insulations have varying maximum and normal
operating temperatures, flexibility, fire resistance, and mechanical
and environmental protection.

Aluminum is a commonly used electrical conductor material due to its
high conductivity, availability, and lower cost.

Copper is also widely used for its desirable electrical and mechanical
properties.


Considerations for isolation and protection include location,
transformer type, and protective measures like overcurrent, groundfault, and differential protection.

Physical isolation may be required to protect occupants and the
public.

The National Electrical Code (NEC) requires conductors of No. 8 AWG
and larger to be stranded.

Adequate working space around electrical equipment is necessary for
various operations, including switchgear removal, fuse replacement,
cleaning, and cable installation.

Stranded conductors are commonly found in portable cords.

Different types of stranded conductors include standard concentric,
compressed, compact, rope, and bunched.

A single insulated or bare conductor is defined as a "conductor," while
an assembly of two or more insulated conductors, with or without an
overall covering, is defined as a "cable."

A comparison can be made between copper and aluminum
conductors.

Aluminum requires larger conductor sizes to carry the same current
as copper.

For equivalent ampacity, aluminum cable is lighter in weight and
larger in diameter than copper cable.

Basic insulating materials are either organic or inorganic.

Mineral insulated cable employs the inorganic insulation magnesium
oxide (MgO).

The aging factors of heat, moisture, and ozone are among the most
destructive to organic-based insulations.

The comparisons include Relative Heat Resistance, Heat Aging, Ozone
Resistance, and Corona Resistance.

Heat Aging - The effect on elongation of an insulation when subjected
to aging in a circulating air oven is an acceptable measure of heat
resistance.

The air oven test at 121 °C is used to grade materials for possible use
at elevated conductor temperatures or in hot-spot areas.

Additional factors to consider include roof structures for vehicular
traffic, potential interferences, future street changes, drainage, spare
conduits, duct separation for primary and secondary feeders, cable tie
lengths, equipment loading balance, and illumination.

Room dimensions should be sufficient to provide access and working
space around electrical equipment for easy operation and
maintenance.

Damping treatment can be applied to reduce noise generated by
transformers.

Isolation techniques can be used to minimize vibration and noise
transmission.

Flexible connections can be implemented to reduce vibration and
noise transfer.



Proper placement of ventilation ducts can help dissipate heat and
reduce noise.
Service rooms and electrical closets should be located as close as
possible to the areas they serve.
Doors should be large enough to allow for easy installation or removal
of electrical equipment.

Electrical rooms and closets should be sized larger than the minimum
criteria dictated by the NEC to allow for future expansion and growth.

Additional utility working space may be required.

The 150 °C oven aging is more severe and is used to compare
materials with superior heat resistance.






Ozone and Corona Resistance - Corona discharge produces
concentrated and destructive thermal effects along with the
formation of ozone and other ionized gases.
Classification of circuits under Article 725: Class 1 power-limited
circuits are restricted to not over 30V and not over 1000VA, while
Class 2 circuits are required to be limited to lower levels of power
than Class 3 circuits.

Moisture Resistance - XLPE, polyethylene, and EPR insulations exhibit
excellent resistance to moisture as measured by standard industry
tests, such as the ICEA Accelerated Water Absorption Test.
Class 2 (CL2) or Class 3 (CL3) power limited circuit cable or power
limited tray cable can be used for remote control, signaling, and
power limited circuits with power levels defined in NEC Article 725.

Electrical design considerations include conductor size, type,
insulation thickness, dielectric strength, insulation resistance, specific
inductive capacitance, and power factor.
These cables are rated 300 V and include copper conductors for
electrical circuits and thermocouple alloys for thermocouple
extension wire.

Type MV power cables have solid extruded dielectric insulation and
are rated from 2001 - 35,000 V.
Thermal design considerations include compatibility with ambient
and overload conditions, expansion, and thermal resistance.

These cables are available as single- and multiconductor cables with
nominal voltage ratings of 5 kV, 8 kV, 15 kV, 25 kV, and 35 kV.

For operating voltages below 2 kV, non-shielded constructions are
typically used.
Mechanical design considerations include toughness, flexibility,
jacketing or armoring, and resistance to impact, crushing, abrasion,
and moisture.

Chemical design considerations include stability of materials when
exposed to oils, flame, ozone, sunlight, acids, and alkalies.

Cables above 2 kV are required to be shielded to comply with NEC and
ICEA Standards.

Flame resistance is important for cables installed in cable trays, and
they should be listed as flame-retardant and marked for installation in
cable tray.

Shielding is the practice of confining the electric field of the cable to
the insulation surrounding the conductor.


Low Smoke - The NEC authorized the addition of the suffix "LS" to the
cable marking on any cable construction that was flame-retardant and
had limited smoke characteristics.
Insulation shields have several purposes, including confining the
electric field within the cable, equalizing voltage stress within the
insulation, protecting the cable from induced potentials, limiting
electromagnetic or electrostatic interference, and reducing shock
hazard.

Toxicity - All electrical wire and cable installed or terminated in any
building in the State of New York after December 16, 1987, should
have the toxicity level and certain other data for the product on file
with the New York Secretary of State.

Cable outer finishes or outer coverings are used to protect the
underlying cable components from environmental and installation
conditions.

Extruded Jackets: Outer coverings, either thermoplastic or vulcanized,
that can be extruded directly over insulation or over electrical
shielding systems.

Low-voltage power cables are generally rated at 600 V, regardless of
the voltage used.

The selection of 600 V power cable is oriented more toward physical
rather than electrical service requirements.

Materials for extruded jackets can withstand service temperatures
from -55 °C to +115 °C.
Commonly used conductors for 600V include EPR or XLPE insulated
cables with or without a jacket.

Fiber Braids: Synthetic or natural fiber materials used for braiding,
wrapping, or serving cables.
Type RHW is used for 75 °C (167 °F) maximum operating
temperature in wet or dry locations.

Metallic Finishes: Used for mechanical, chemical, or short-time
thermal protection of cable components.

Commonly Used Shielded and Nonshielded Conductors are also
mentioned.

Installation and operating conditions are not specified in the text.

Interlocked Armor provides mechanical protection with minimum
reduction in flexibility.

Interlocked galvanized steel armor should be avoided on singleconductor AC power circuits due to high hysteresis and eddy current
losses.

Corrugated Metal Sheath has corrugations formed perpendicular to
the cable axis and offers mechanical protection equal to or greater
than interlocked armor but at a lower weight.

Lead Sheath, made of pure or alloy lead, is occasionally used for
moisture protection in underground manholes, tunnels, or
underground duct distribution systems subject to flooding.

Aluminum or Copper sheaths, either extruded or die-drawn, are used
for weight reduction and moisture penetration protection in certain
applications.

Wire Armor: Provides significant mechanical protection and
longitudinal strength through the use of spirally wrapped or braided
round steel armor wire.

Single-Conductor and Multiconductor Constructions: Singleconductor cables are easier to handle and can be furnished in longer
lengths compared to multiconductor cables. Multiconductor
constructions have smaller overall dimensions, which is
advantageous in limited space.

Cable Ratings - Voltage Ratings: The selection of the cable insulation
(voltage) rating is based on the phase-to-phase voltage of the system,
whether it is grounded or ungrounded, and the time it takes to clear a
ground fault on the system with protective equipment.



Type RHH is used for 90 °C (194 °F) in dry locations only.

Type RHW-2 is used for 90 °C (194 °F) maximum operating
temperature in wet and dry locations.

Type XHHW is commonly used for 600V XLPE or EPR insulated
conductors without a jacket, with a maximum operating temperature
of 75 °C (167 °F) in wet locations and 90 °C (194 °F) in dry locations
only.

Type XHHW-2 is commonly used for 600V XLPE or EPR insulated
conductors without a jacket, with a maximum operating temperature
of 90 °C (194 °F) in both wet and dry locations.

Type THWN is commonly used for 600V PVC insulated conductors
with a nylon jacket, with a maximum operating temperature of 75 °C
(167 °F) in wet or dry locations.

Type THHN is commonly used for 600V PVC insulated conductors
with a nylon jacket, with a maximum operating temperature of 90 °C
(194 °F) in dry locations only.

Type THW is commonly used for 600V PVC insulated conductors
without a jacket, with a maximum operating temperature of 75 °C
(167 °F) in wet or dry locations.

These conductors are suitable for installation in conduit, duct, or
other raceway, and may be installed in cable tray (1/0 AWG and
larger) or direct buried if NEC requirements are satisfied.

Metal Clad Cable, Type MC: A multiconductor cable with either an
interlocking tape armor or a continuous metallic sheath, suitable for
installation in various environments.

Power and Control Tray Cable, Type TC: A multiconductor cable with
an overall flame-retardant nonmetallic jacket, suitable for use in cable
trays and raceways.

Load current criteria refer to parameters, standards, or guidelines
that govern the current ratings and characteristics of electrical loads
in various systems.

Locating cable faults is a common problem that needs to be
determined for repairs.

Emergency overload criteria determine the normal loading limits of
insulated wire and cable, based on practical experience, to ensure the
most economical and useful life of the cable systems.

Factors to consider in locating cable faults include the nature of the
fault, type and voltage rating of the cable, value of rapid location of
faults, frequency of faults, and experience and capability of personnel.

Voltage-drop limitations are considered in conductor selection.

Physical evidence of the fault, such as observation of a flash, sound, or
smoke, can help locate the fault.

Fault current criteria are taken into account in conductor selection.

Number of conductors in cable and phase identification required

Frequency criteria and hot-spot temperature criteria are factors to
consider in conductor selection.

Conductor size (AWG, kcmil) and material

Insulation type (rubber, polyvinyl chloride, XLPE, EPR, etc.)

The length of cable in elevated ambient temperature areas is
considered in conductor selection.

Voltage rating and insulation level required (100%, 133%, or 173%)

Equipment termination requirements are taken into account in
conductor selection.

Shielding system required for systems rated 8 kV and above, and may
be required for systems rated over 2001-8000 V

The NEC recommends that the steady-state voltage drop in power,
heating, or lighting feeders be no more than 3%.

Installation approvals required (cable tray, direct burial, messenger
supported, wet location, exposure to sunlight or oil, etc.)

The total voltage drop, including feeders and branch circuits, should
be no more than 5% overall.

Busways originated as a result of a request from the automotive
industry in Detroit in the late '20s for an overhead wiring system.

The distance between the source and the load should be kept as short
as possible in wiring systems layout.

A busway consists of bare copper conductors supported on inorganic
insulators mounted within a nonventilated steel housing.

Open-wire construction consists of single conductors on insulators
mounted on poles or structures.

There are four types of busways: feeder busway, plug-in busway,
lighting busway, and trolley busway.

The conductors may be bare or have a covering or jacket for
protection against corrosion or abrasion.

Feeder busway is used to transmit large blocks of power and has a
low and balanced circuit reactance for voltage control.

Aerial cables may be self-supporting or messenger-supported and can
be attached to pole lines or structures.

Plug-in Busway: Used in industrial plants as an overhead system to
supply power to utilization equipment with current ratings from 1004000 A.

Self-supporting aerial cables have high tensile strength conductors for
this application.

Lighting Busway: Rated at a maximum of 60 A, 300 V to ground.

Open runs are a low-cost method that utilizes adequate support
surfaces between the source and the load.

Trolley Busway: Constructed to receive stationary or movable takeoff
devices.

It is useful in combination with other methods, such as branch runs
from cable trays, and when adding new circuits to existing
installations.

Standards: NEC Article, ANSI/UL 857-1989, Busways and Associated
Fittings, NEMA BU1-1988.


Cable tray is a rigid structure made of metal or noncombustible
material used to support cables.
Busways Over 600 V (Metal-Enclosed Bus): Referred to as "metalenclosed bus" and consists of three types: isolated phase, segregated
phase, and nonsegregated phase.

Cable bus is used for transmitting large amounts of power over short
distances.

Metal-enclosed bus was included in the 1975 NEC.

The metal-enclosed bus nameplate must specify its rated voltage.

Conduit made of rigid steel provides the greatest mechanical
protection for above ground conduit systems.

The metal-enclosed bus nameplate must specify its continuous
current.

The metal-enclosed bus nameplate must specify the frequency.

The metal-enclosed bus nameplate must specify the 60 Hz withstand
voltage.

The metal-enclosed bus nameplate must specify the momentary
current.


Direct burial is when cables are buried directly in the ground without
the need for conduit, typically when future maintenance is not
anticipated.
Terminations electrically connect insulated cable conductors to
electrical equipment, physically protect and support the end of the
cable conductor, and control electrical stresses for desired insulation
levels.

Splicing devices and techniques are used to join or connect cables
together.
CHAPTER 9: Effects and Protection of Faults in
Power Systems

Tape splices can be used for shielded cables, and the considerations
are similar to nonshielded cables.


Preassembled splices provide a moistureproof seal to the cable jacket
and are suitable for submersible, direct burial, and other applications.
Uncontrolled short-circuit faults can cause service outages,
interruption of essential facilities or vital services, extensive
equipment damage, fire damage, and possibly personnel injury or
fatality.


Grounding of cable systems is important for safety and proper
functioning.
Short-circuit is an overcurrent resulting from a fault of negligible
impedance between live conductors having a difference in potential
under normal operating conditions.

Cables rated up to 35 kV in power distribution systems have strong
insulation to compensate for installation handling and potential
deterioration.

Electric power systems should be as fault-free as possible through
careful system and equipment design, proper installation, and
maintenance.

Testing in a wiring system is important for safety, reliability, and
compliance with electrical codes and standards.

Faults can occur due to loose connections, voltage surges,
deterioration of insulation, vermin or rodents, seepage from concrete,
etc.

Various tests and inspections are performed at different stages of the
wiring system's lifecycle.






Arcs, flashes, and burning can occur at the fault location with
consequent smoke generation from the fuel load of combustibles.

"Symmetrical current envelopes" refer to envelopes of peak current
waves that are symmetrical around the zero axis.
Increased current flows from various sources to the fault location,
causing increased thermal and mechanical stress on components.

"Asymmetrical current envelopes" have peaks that are not evenly
distributed around the zero axis.
Voltages decrease throughout the system during a fault, with
maximum voltage drop occurring at the fault location.

Most short-circuit currents are initially asymmetrical, but gradually
become symmetrical over a few cycles.
Enclosures in contact with live conductors can experience elevated
voltages, increasing the risk of electric shock.

Short-circuit currents are typically asymmetrical in the first cycle
after the short circuit.
Circuit protecting devices such as circuit breakers and fuses are used
to disconnect faults from the power system.

Protective devices should be capable of interrupting the maximum
short-circuit current, which can result in a bolted fault at the device
location.
The symmetrical component of short-circuit currents is at a maximum
at the beginning of the short circuit and then decays to a steady-state
value due to changes in machine reactance.

In practical circuits with resistance, the DC component of
asymmetrical currents diminishes to zero as its energy is released as
an I²R loss in the circuit's resistance.

The total short-circuit current is a combination of currents from the
utility, local generator, synchronous motor, and induction motor, and
it decays over time due to the reduction of flux in the machine.

The induction motor component of the total short-circuit current
usually disappears after one or two cycles, except for very large
motors where it may be present for longer.

Three-phase bolted fault: Conductors are physically connected with
zero impedance, like being bolted together. Not the most common
fault but leads to maximum short-circuit values.
Fault currents can vary depending on the location of the fault and the
impedance of the circuit elements.

Line-to-Line bolted fault currents are about 87% of the three-phase
bolted fault.
Accurately calculating available fault currents is necessary to ensure
proper protection and avoid short circuit and fire hazards.

Line-to-Ground Bolted Faults: In solidly grounded systems, line-toground fault current is usually similar to the three-phase bolted fault
current, but ground-fault current is generally lower due to the
relatively high impedance of the ground return circuit.

Resistance Grounded High-Voltage Systems: In resistance grounded
high-voltage systems, a resistor is selected to limit ground-fault
current within a range of 1-2000 A, and complex line-to-ground shortcircuit current calculations are generally unnecessary.

The fault condition with no impedance results in a maximum shortcircuit current, known as the available short-circuit current.

Bolted short circuits are rare, and faults typically involve arcing and
burning, leading to lower fault currents.

Faults involving ground can lead to elevated potential in the
protective enclosure, increasing the risk of shock hazard.

Maintaining adequate equipment grounds and quickly detecting and
isolating faults are important for minimizing exposure voltage and
reducing the duration of exposure.



Implementing proper grounding techniques can reduce elevated
potential and minimize the risk of shock to personnel.

Continuous monitoring and regular maintenance of equipment can
aid in the early detection and isolation of faults, ensuring a safer
working environment.

Circuit breakers and fuses can be designed for single- or multiple-pole
use and have both protective and switching functions.

Arcing Faults: Arcing faults in power systems have lower short-circuit
currents than bolted faults.
Single-phase voltage issues can result from utility supply failure,
system defects, or single-pole interrupters.

Arcing faults are challenging to detect and can pose safety risks.

There are four basic sources of short-circuit currents.

Arcing faults can cause damage from the effects of sustained arcs.

The impedance of a rotating machine consists primarily of reactance,
which is complex and variable with time.

Equipment selection is crucial for personnel safety, equipment
protection, and service continuity.

Reactance of a rotating machine changes with time and affects current
values in response to short circuits.

Protective devices such as fuses and certain circuit breakers operate
based on current detection.

Devices can handle higher short-circuit currents than their rating
with upstream current-limiting measures.

A wide range of protective relays is available to detect abnormal
conditions related to voltage, frequency, or real/reactive power.

Rotating machines are assigned three reactance values for calculating
short-circuit currents: subtransient reactance, transient reactance,
and synchronous reactance.

Relays should be used alongside circuit breakers or motorized
switches to remove detected faults.


Subtransient reactance (Xd'') is the apparent reactance of the stator
windings at the instant of a short circuit and determines initial
current flow.
Circuit protective devices should be chosen to swiftly detect and
interrupt faults without exceeding equipment ratings.

Proper selection depends on knowledge of expected short-circuit
current magnitudes for various fault types.
Transient reactance (Xd') determines the current after the
subtransient period, typically up to 0.5 seconds.

Use equipment with short-circuit ratings equal to or higher than
potential short-circuit currents for safety and equipment protection.

ANSI/NFPA 70-1990, National Electrical Code (NEC), Section 110-9
states that devices intended to break current should have an
interrupting rating sufficient for the voltage and current.

Selection of a specific device depends on factors such as protective
characteristics, economics, component protection, maintainability,
and user preference.

Components like busway and conductors must exceed the let-through
currents of overcurrent protective devices if lower than the calculated
short-circuit current at the fault point.

The type of short-circuit calculation depends on the basis for rating
interrupting devices and their operating.




Synchronous reactance (Xd) determines the current flow when
steady-state condition is reached but is not used for short-circuit
calculations.
Obtain the available utility three-phase short-circuit current and
three-phase short-circuit X/R ratio from the serving utility.

Primary voltage should be adjusted by considering transformer
impedance and voltage ratio.

Single line-to-ground short-circuit current and X/R ratio should be
obtained from the serving utility for accurate calculations and
analysis.

"Symmetrical" describes AC waveforms with evenly distributed peaks
around the zero axis.

Unusual circuit configurations can subject devices to asymmetrical
currents beyond their capabilities.

The geometric relationship between the eye, task, and light source is
the primary factor in minimizing veiling reflections.

Short-circuit calculations should consider the X/R ratio at the fault
point to determine power factor.

Special lighting materials can be useful when achieving ideal
geometry is challenging, especially in multi-occupancy rooms.

Asymmetrical multiplying factors based on X/R ratio and circuit
power factor can be estimated using available data.

Visual comfort probability (VCP)


Short-circuit current may change over time post-fault.
Glare evaluation data have been developed through an empirically
derived formula that assesses all the factors in a room.

Device speed and rating basis determine the circuit impedances in the
equation I = E/Z.

Visual comfort probability (VCP) is a system that determines the
brightness tolerances of individuals based on statistical testing.

Total Current Basis of Rating is used in ANSI C37.6-1971 for highvoltage circuit breakers.

VCP tables for specific luminaires can be obtained from luminaire
manufacturers.

ANSI C84.1-1989 lists 1000-100,000 V as "medium voltage".


IEEE C37.5-1953 provides methods for determining the Rms value of
a sinusoidal current wave and simplified calculation of fault.
Air return luminaires allow for the transfer of air from occupied areas
to the mechanical room through the luminaire lamp compartment and
ceiling cavity.

Advantages of task-ambient lighting: Energy-efficient.

ANSI C37.5-1969 introduced a revised calculation procedure for
obtaining short-circuit duties for total current rated circuit breakers.

Electric lighting revolutionized commercial buildings, replacing
daylight as the primary source of illumination.

Despite advancements, lighting still consumes 40% of commercial
building energy.

The calculation of first-cycle duty (momentary) was determined by
ANSI C37.5-1953 using a symmetrical short-circuit current value and
multiplying factors to find asymmetrical short-circuit duty.

ANSI C37.5-1969 modified the reactance values for small and
medium-sized induction motors in the first-cycle duty calculation.

Lighting objectives for owners may vary depending on the desired
visual performance or creating mood and atmosphere.

ANSI C37.5-1969 used subtransient reactance for generators, 1.5
times subtransient reactance for motors, and modified subtransient
reactances for induction motors.

The Department of Energy (DoE) created "The Model Code for Energy
Conservation in New Buildings" to mandate energy conservation.


Low-voltage protective devices are rated based on the maximum
available symmetrical current at a specified power factor, using
subtransient reactance X²d for all short-circuit current sources.
The Federal Energy Administration (FEA) requested that states adopt
a mandatory lighting efficiency standard at least as stringent as
ANSI/ASHRAE 90-80, Section 9.


High-voltage circuit breakers are rated on a symmetrical current basis,
with the symmetrical short-circuit current rating applying only at the
rated maximum voltage.
On May 6, 1987, the DoE proposed "Energy Conservation Voluntary
Performance Standards for New Commercial and Multi-Family HighRise Residential Buildings" in the Federal Register.


The short-circuit capability at lower actual operating voltages is
calculated by multiplying the rated current by the voltage.
Ballast: An electrical device used with discharge lamps to supply
voltage, control lamp current, and provide power factor correction.


IEEE C37.010-1979 describes the method for applying symmetrically
rated circuit breakers.
Brightness: The subjective attribute of any light sensation, including
qualities such as "bright," "light," "brilliant," and "dim."


The first-cycle duty calculation is similar to IEEE C37.5-1979.
Brightness refers to measurable photometric brightness, while
"luminance" is the preferable term for objective measurements.

Contact parting time short-circuit duty calculation in IEEE C37.0101979 uses the same reactance network as C37.5-1979.

Contrast indicates the degree of difference in light reflectance
between the details of a task and its background.

A multiplying factor is applied to establish duty for comparison with
symmetrically rated circuit breakers.

Coefficient of utilization (CU) is the ratio of the average lumens
delivered by a luminaire to a horizontal work plane to the lumens
generated by the luminaire's lamps alone.

If the X/R ratio is 15 or less, the multiplying factor is 1.0. When the
X/R ratio exceeds 15, the factor is determined based on contact time.

Efficacy is measured in lumens per watt (lm/W).

The fault point X/R ratio calculation in IEEE C37.010-1979 is the
same as in IEEE C37.5-1979.

There are different types of light sources, including incandescent
lamps, fluorescent lamps, and High-Intensity Discharge (HID) lamps.

Calculation methods in IEEE C37.5-1979 and IEEE C37.010-1979
differ from ANSI C37.5-1953, primarily in data collection and the
treatment of reactances.

Equivalent Sphere Illumination (ESI) is a measure of the effectiveness
of a lighting system in rendering a task visible compared to the
visibility of the same task lit inside a sphere of uniform luminance.

The first-cycle (momentary) duty calculated by present methods is
generally similar to the earlier method.

A fixture is a luminaire.

Footcandle (fc) is a unit of illuminance.

The interrupting duty calculated by the present method is often
higher due to increased recognition of factors.

Footlambert (fl): The unit of luminance that is defined as 1 lm
uniformly emitted by an area of 1 ft2.

Further details about these procedures can be found in IEEE Std 1411986, IEEE Recommended Practice for Electric Power Distribution for
Industrial Plants.

Glare: The undesirable sensation produced by luminance within the
visual field.

Lamp: Generic term for a man-made source of light.

High-intensity discharge (HID) lamps: A group of lamps filled with
various gases.

Lumen (lm): The international unit of luminous flux or the time rate
of the flow of light.

Illuminance: The unit density of light flux that is incident on a surface.
CHAPTER 10: Energy Conservation and Lighting
Regulations

Lighting contribution to building heating and cooling loads

Lighting control techniques like polarizing materials, specific light
distributions, and indirect lighting aim to reduce veiling reflections in
visual tasks.

Luminaire: A complete lighting unit that consists of parts designed to
position a.




Electric light sources and daylight have different characteristics in
terms of efficacy, color, source size, lumen maintenance, starting and
restarting attributes, and economics.
Lumens per watt (lm/W): The ratio of lumens generated by a lamp to
the watts consumed by the lamp.

Incandescent lamps have low efficacies ranging from 17 to 24 lm/W,
making them the least efficient lighting source.
Luminaire efficiency: The ratio of lumens emitted by a luminaire and
the lumens generated by the lamp(s) used.

They can be energy-efficient when used for spotlighting in small areas
from a distance, but are not suitable for large, long-operating spaces.
Luminance: The light emanating from a light source or the light
reflected from a surface, measured in cd/m2.

Incandescent lamp life and efficacy have an inverse relationship, with
lower filament temperatures resulting in longer lamp life but reduced
efficacy.

The selection of the right lamp life for incandescent lamps depends on
factors such as energy costs, maintenance labor rates, and ease of
access.

Incandescent lamps provide good color rendering despite their warm
color bias and limited cool colors. Additional colors can be achieved
with filters applied to the bulbs or separate color filters in theatrical
and display lighting.

Tungsten halogen lamps: They use the halogen cycle to prevent
deposits of evaporated tungsten from collecting on the inner bulb
surface, resulting in a longer lamp life and consistent lumen output.

Incandescent lamps (dimming): These lamps can be dimmed by
adjusting the voltage at the socket, but this reduces light output and
lamp efficiency.

Fluorescent lamps: These lamps rely on an electric arc discharge
through low-pressure mercury vapor to produce ultraviolet radiation,
which then excites phosphors on the lamp's bulb wall to produce
visible light.

Fluorescent lamps are more energy-efficient compared to
incandescent or mercury lamps.

The efficacy of fluorescent lamps varies based on factors like color
and wattage.

Fluorescent lamps offer advantages such as low brightness and
diffusion, making them suitable for applications where minimizing
glare and controlling discomfort glare is essential.

Fluorescent lamps come in various lengths and can operate at
different currents.

Rapid-start and slimline lamps typically use 430 mA, but ballasts
allow these lamps to be operated at reduced currents like 200 mA or
300 mA.

Lux: The metric measure of illuminance, equal to 1 lumen uniformly
incident upon 1 m2.

Reflectance: The ratio of the light reflected by a surface to the light
incident.

Rated life of a ballast or lamp: The number of burning hours at which
50% of the units have burned out and 50% have survived.

RVP (performance): The potential task performance based upon the
illuminance and contrast of the lighting system.

Veiling reflections: Reflected light from a task that reduces visibility
because the light is reflected specularly from shiny details of a task,
which brightens those details and reduces contrast with the
background.

Electronic ballasts operate at higher frequencies for increased system
efficiency.

Task-ambient lighting: A concept involving a component of light
directed toward tasks from appropriate locations by luminaires
located close to the task for energy efficiency.

VCP (visual comfort probability): A rating of a lighting system
expressed as a percentage of people who, if seated at the center of the
rear of a room, will find the lighting visually acceptable in relation to
the perceived glare.

Visual task: Work that requires illumination in order for it to be
accomplished.

Work plane: The plane in which visual tasks are located.

Providing illumination without discomfort caused by glare.

Minimizing veiling reflections in task details.

Using a high color rendering source for critical appearances.

Selecting sources and luminaires that provide sparkle and modeling
on certain objects.

High-output fluorescent lamps operate at 800 mA and offer around 45%
more light per unit of length compared to 430 mA lamps.
Using sources, equipment, and techniques to create the desired
atmosphere in a space.

Extra-high-output fluorescent lamps at 1500 mA provide 60% to 70%
higher light output per unit length.
Visual Comfort - providing illumination without annoyance or
discomfort.

High-output lamps cater to applications requiring increased
illumination levels or where higher mounting heights allow for
reduced lamp or fixture quantities, offering cost savings.

Reduced wattage fluorescent lamps have been developed to reduce
power consumption by 10% to 20% across various types, while
providing improved luminous efficacy, color rendering, and longer
average lamp life.

Reduced wattage fluorescent lamps are suitable for energy-efficient
lighting installations while maintaining illumination levels and can
replace incandescent options.

It is important to avoid using reduced wattage fluorescent lamps in
areas below 60 °F.

Fluorescent lamps offer various colors achievable by changing
phosphor components.

Improved technology allows for high-efficiency, high-color-rendering
lamps, albeit at a higher cost.



Minimizing veiling reflections to improve task visibility.

Room finishes and their reflectance play a role in the efficient
utilization of light and lighting energy.

The color scheme and light source can impact the perception of
temperature by occupants of the space, potentially affecting space
heating or cooling.

Different light sources can vary in terms of their efficacy of light
production and color rendition.

Psychological factors, although subjective, have been studied to
understand how groups of people react to different lighting
conditions.



The Illuminating Engineering Society (IES) adopted a new system for
recommended illumination levels in 1979, replacing single-number
footcandle values with illuminance ranges aligned with international
standards.

Designers now have the responsibility to select illumination levels
based on factors such as worker age, task background reflectance, and
performance demands.
Some fluorescent lamps provide saturated colors using specific
phosphors or integrated color filters.

The starting and operating characteristics of fluorescent lamps are
significantly affected by temperature.
Equivalent Sphere Illumination (ESI) is a useful metric for comparing
lighting systems.

Dimming systems are available for 30W and 40W rapid-start
fluorescent lamps, expanding their use in various settings.



Fluorescent lamps (dimming): Electronic dimming systems vary, so
consulting manufacturers is essential for details on features,
reliability, and cost. Special ballast designs enable the flashing of highoutput fluorescent lamps for signs and displays.
High-intensity discharge (HID) lamps: This lamp family includes
mercury metal-halide, high-pressure sodium, and low-pressure
sodium lamps. They require ballasts and have a higher pressure in
their arc tubes and a more intense, shorter discharge path compared
to fluorescent lamps.
High-intensity discharge (HID) lamps (mercury lamps): Mercury
lamps, once commonly used, are now less specified due to the
availability of more efficient options like metal-halide and highpressure sodium lamps. They are still suitable for lower wattage
applications around 175 W.

Special low-temperature ballasts are available for starting lamps in
extremely cold conditions.

Ballasts may overheat when lamps flicker near the end of life or when
one of a pair of lamps is removed from the lampholder.

Flickering or burned-out lamps should be replaced promptly to
prevent possible ballast damage.

Lamps remaining in energized fixtures cause the ballast to consume a
small amount of energy at a very low power factor due to magnetized.

Electronic ballasts for high-pressure sodium lamps have solid-state
control circuits and reactors that monitor operating conditions.

It is desirable to use an in-line fuseholder and time delay fuse with
each fluorescent lamp ballast to prevent blackouts and provide a safe
means of replacing ballasts.

Circuit breakers used for frequent switching of fluorescent lamps
should be UL listed as "SWD" for this duty.

Radio interference from fluorescent lighting systems can be
minimized by using appropriate lenses on the luminaire and installing
available filters in the circuit feeding the ballasts.

Most aspects of ballasts in fluorescent lamps also apply to HID lamps.

High-pressure sodium lamp ballasts have a high-voltage pulse for
lamp starting and hot-restart capability within a minute after voltage
interruptions.

Older ballasts required prompt lamp replacement and avoiding
keeping them energized without a functioning lamp to prevent
damage to the starting aid.

HID ballasts should be grounded in compliance with the NEC or local
codes.

Luminaires for air return and their effect on air changes, fan
horsepower, etc.

It may be desirable to use a line-side fuse with HID ballasts to prevent
branch-circuit breakers from opening in the case of a defective ballast.

Lag- and reactor-type ballasts should have a supply voltage within ±
5% of the design voltage, while constant wattage autotransformer
(CWA) ballasts should have a voltage within ± 10% of the design
voltage. HID ballasts are available for a wide variety of utilization.

Metal-halide lamps are more efficient than mercury lamps and should
be used when color is important.

Mercury and metal-halide lamps produce ultraviolet energy within
their arc discharge, which can enhance color rendition.

Mercury lamps have safety features that deactivate the lamp shortly
after the outer bulb is damaged.

Starting characteristics of mercury and metal-halide lamps are
relevant considerations.

Lamps require 5-8 minutes of starting time (warmup) before
reaching full light output due to low vapor pressure of the arc tube
gases at the start.

High-intensity discharge (HID) lamps, such as high-pressure sodium
lamps, have a relatively high-pressure electric arc discharge in a
ceramic arc tube containing sodium in an amalgam form.

Low-pressure sodium lamps have the highest lm/W efficacy but may
not be acceptable for color recognition.

HID lamps are larger in size compared to low-pressure sodium lamps
and more similar to fluorescent lamps.

Care should be taken in disposing of low-pressure sodium lamps as
the free sodium in contact with water can create a fire hazard.

Ballasts for high-intensity lamps perform several functions, including
providing the appropriate voltage to start and maintain the lamp, as
well as power factor correction.

The primary choice for fluorescent lamps is the rapid-start ballast,
which allows for quick lamp ignition and comes in various current
options.

Architectural character of the space to be lighted, including size,
proportions, layout of furnishings, and structural and mechanical
features, should be considered.

Solid-state electronic ballasts, introduced in the 1980s, improve
power factor but their harmonic currents should be considered to
avoid overloading neutral circuits.

The designer's concept of how the space should appear, including
lighting patterns that emphasize structure or layout, should be taken
into account.

According to ANSI/NFPA 70-1990, all fixtures and lighting equipment,
including ballasts, should be grounded.

The styling of luminaires, whether simple or decorative, should be
considered, noting that decorative luminaires may be primarily for
decorative effect rather than illumination.

Rapid-start ballasts require a starting aid consisting of a grounded
metal strip running the full length of the lamp.

General considerations that affect the selection of a lighting system
include the appropriateness of the luminaires for providing
illumination and the presence of other lighting systems, such as cove
lighting or downlighting systems.

Suitability for specific visual tasks or activities, including light
distribution, diffusion or directional qualities, creation of shadows,
veiling reflections, and uniformity of illumination.

Visual comfort, including the use of appropriate shielding and
diffusing media, opaque or luminous-sided luminaires, viewing
orientation, and visual comfort probability (VCP).

Efficiency, including the utilization of direct, indirect, and
intermediate types of lighting, and power requirements.

Flexibility, including the use of movable office furniture with task
lighting fixtures, movable shelf-mounted fixtures, movable freestanding indirect fixtures, and movable plug-in recessed troffers.
Maintenance, including the susceptibility to maintenance
requirements.

The fluorescent fixture housing acts as a starting aid.

Slimline lamps are instant-start lamps that can operate at various
currents based on the chosen ballast, with the two-lamp series type
being the most popular and economical option.

Lead-lag ballasts operate lamps in parallel to achieve a high-power
factor circuit, but are more expensive than the series type.

Recent fluorescent lamp ballasts reduce losses by almost half, run
cooler, and last longer than traditional ballasts.

Ballasts should be operated at no more than 5% higher or 10% lower
than the rating to avoid overheating and shorten life.

Ambient temperature and fixture design can affect ballast
performance.

Ballast case hot-spot temperature should not exceed 90°C (194°F)
during operation.


Thermally protected ballasts disconnect when temperatures exceed
the limit, while those without thermal protection have shortened
lifespans when operated above 90°C (194°F).
-Dirt collection
-Ease of cleaning
-Ease of relamping
-Characteristics of plastics, paints, and metals used
-Coordination with mechanical system
-Luminaires for air supply

An alternative approach is to bypass the luminaire and return air
directly to the ceiling cavity, which offers similar benefits but to a
lesser extent.

Benefits of using air return luminaires or bypassing luminaires for air
return include reduced heat gain in occupied space, reduced
requirement for air exchanges, reduced duct size and fan horsepower,
and improved thermal comfort.

Using air return luminaires or bypassing luminaires can also result in
reduced fluorescent lamp.

Reduced ballast operating temperature and longer life for older
conventional ballasts.

There is little effect on the life of low-watt loss ballasts.

Several lighting techniques may be evaluated for specific applications.

The purpose of the lighting system should be established before
discussing lighting techniques for commercial buildings.

Functional requirements for each area of the building should be
clearly defined.

Seeing clearly is crucial for task performance and the quantity and
quality of light affect this requirement.

Tools like visual comfort probability, contrast rendition factor, and
equivalent sphere illuminance help assess the quality of light.

Circuit breakers are not recommended as switches for lighting control
unless designed for such a purpose.

Approved 300 V wall switches can safely control lighting fixtures on
277 V circuits if voltage between switches remains below 300 V and
grounded barriers are used when it exceeds.

Two phases of a 480 V system sharing the same enclosure should
have a voltage of 300 V according to NEC guidelines.

Low-voltage remote control switching systems typically use a 24 V
switch to actuate relays in the branch circuit for convenient and
flexible control.

Lighting contactors are used for controlling large groups of lighting or
multiple branch circuits, with different standard control voltages such
as 24 V dc, 24 V ac, 120 V ac, and 277 V ac.

Advanced control systems with microprocessor logic and
multiplexing are emerging to reduce wiring complexities in lighting
control.

Solid-state semiconductor dimmers have simplified the practice of
dimming incandescent lamps and are popular due to their small size.

Solid-state technology enables efficient dimming of HID lamps,
providing energy savings while maintaining a constant level of
illumination.

Possible methods of dimming include variable resistance (rheostat),
variable autotransformer, variable reactance, and solid-state
electronics.

Dimming systems are suitable for various applications, both indoors
and outdoors, offering flexibility in energy management.

Lighting maintenance should be in accordance with the plans of the
lighting system designer.

Illuminance plays a key role in creating varying moods within spaces.

Lighting can guide people's movement through spaces.

Aesthetic lighting focuses on enhancing the visual appeal of objects
and people.

Light loss in lighting systems due to dirt, dust, and environmental
conditions varies based on the fixture type and cleaning frequency.

Uniform lighting: Even illuminance throughout the area at task
lighting level.

Proper maintenance planning during design can significantly reduce
the need for relamping and cleaning.

Non-uniform lighting: Most light on the task, with general and noncritical levels reduced.

Light loss factors acknowledge uncontrollable depreciation and
controllable factors in depreciation.

Task-ambient lighting: Direct lighting for task up close with ambient
lighting from adjacent indirect or ceiling-mounted luminaires.

Lumen maintenance data from manufacturers helps evaluate light
output over time.

Advantages of uniform lighting: Good eye adaptation, uniform
appearance, energy-efficient, lower initial cost, provides space
interest, emphasizes work areas.

Planned maintenance, including relamping and cleaning, prevents
burn-outs, maintains illumination levels, and saves on labor and
expenses.

Advantages of non-uniform lighting: Energy-efficient, tax benefits,
easily movable.

Group relamping and coordinated cleaning are cost-effective for
lamps with similar life spans and operating hours.

Disadvantages of uniform lighting: May be least energy-efficient,
monotonous, may have higher initial cost.

The efficiency, light output, life, and power consumption of lamps are
all substantially affected by their operating voltage.

Disadvantages of non-uniform lighting: Must know tasks, task
locations, must be moved as task changes.

Incandescent lamp performance, including efficiency, light output,
lifespan, and power usage, depends significantly on their operating
voltage.

Disadvantages of task-ambient lighting: Veiling reflections, space
confining, expensive fixtures, wiring and switching may be more
difficult.

The most common standard voltage for general-service incandescent
lamps is 120 V.

Typical uses: Large homogenous areas, libraries, drafting rooms

Higher voltage options like 230 V, 250 V, and 277 V are available but
are generally less efficient and durable.

Typical uses: Clerical offices, supermarkets, cafeterias


Typical uses: Gymnasiums
Using lower voltage incandescent lamps in higher voltage sockets can
cause them to shatter.

Typical uses: Large non-homogenous areas, smaller areas, private
offices, low employee density areas

Lamp efficiency is often more critical than lamp life for incandescent
lamps.

Typical uses: Small work areas, furniture systems, open office plans

Special-service incandescent lamps with longer lifespans exist, but
they are about 15% less efficient than general-service lamps.

Control of lighting in large homogenous areas is typically done
manually by means of a switch located in a luminaire, a pull cord
attached to the luminaire switch, or a fixed wall switch.

Fluorescent lamps require proper ballast for optimal performance.

Manufacturers provide recommended voltage limits for specific
ballasts, with using 277 V and 480 V primary ballasts for HID lamps
resulting in cost savings in commercial buildings.

Connecting fluorescent luminaires line-to-neutral in 480Y/277 V
power supply systems can be economical, but may introduce third

Control of lighting in large non-homogenous areas, smaller areas,
private offices, and low employee density areas can be done manually
with a switch or pull cord, or more sophisticated options such as
dimming and timed controls can be achieved through manual or
automatic means.
harmonic currents that require the neutral conductor to match the
size of other circuit conductors as per NEC regulations.


Incandescent filament lamps have a power factor of 100%, while
fluorescent and HID lamps typically operate at a power factor of less
than 50% due to ballast circuits with reactive elements.
Most ballasts for general lighting applications can enhance the power
factor.

Two-lamp series fluorescent ballasts have a slightly leading power
factor, which is advantageous in buildings with other loads having a
lagging power factor.

High-power-factor ballasts are recommended for lighting applications.

Some ballast circuits used in devices like desk lamps and home
appliances may operate low-wattage fluorescent lamps at a low
power factor.

Fixtures can vary in cost and quality due to factors like workmanship
and reflector type.

Lighting designers should consider overall economic factors when
selecting fixtures, as the most expensive may not always be the best
choice and the least expensive may not be the wrong choice.

Effective communication between the lighting designer and the client
is important in determining the appropriate lighting type and quality
based on factors such as task characteristics, light source quality,
visual comfort, lighting control, required light levels, and budget.

Energy costs vary by state and region, and while energy efficiency is a
concern for designers, clients are often more concerned with energy
economics.

The lighting designer should consider the cost of the lighting in
relation to its energy efficiency and the client's budget.

Maintenance: Lighting designers should consider the maintenance
details from the client, taking into account the size and expertise of
their maintenance department.

High temperatures may shorten the life of ballasts, with thermal
protectors opening the circuit and turning off the light.

Incandescent lamps perform well in varying temperatures, while HID
and fluorescent lamps are greatly impacted by cold temperatures.

Low-maintenance systems can be costlier upfront, so a balance
between maintenance and system costs should be considered.
Appropriate ballasts are necessary to provide sufficient starting
voltage for lighting.

Effect on Personnel: The psychological effects of illumination on
workers should be discussed with the end user to make informed
decisions about the lighting system.

Productivity is a key consideration, and the trade-off between
production levels and illumination quality should be evaluated when
preparing the illumination budget.

Illuminance calculations: Two principal factors in lighting design are
illuminance calculations and life-cycle costs.

Illuminance calculations can be approached in two main ways:
uniform distribution for densely occupied spaces like offices and
classrooms, and non-uniform distribution for energy-efficient task
lighting.

For uniform illuminance, utilization coefficients from luminaire
manufacturers, combined with maintenance factors, determine the
number and arrangement of luminaires.

Non-uniform illuminance calculations are more complex, involving
direct luminaire contributions and interreflected light, often done
point by point.

Lighting in buildings can serve a dual purpose in the winter by
providing both illumination and replacing heat losses when the
outside temperature is low, with electric lamps being 100% lowtemperature heat source.

It is important to assess each subsystem's impact on energy usage in
future building designs to comply with energy budgets and ensure
efficiency.

Three variables to consider in computing the net effect of lighting on
building energy usage are the lighting energy used directly, the heat
gain on a cooling system caused by lighting load, and the lighting heat
gain contribution to building heating.

Lighting systems in winter can help maintain room temperature and
reduce the need for frequent heating system cycling, especially when
using oil or natural gas for space heating.

Ceiling-installed lighting units in single-story buildings compensate
for heat loss through the roof when the outside temperature drops
below 65 °F (18.3 °C).


Ballasts should be designed to withstand low temperatures.

Placing the ballast in a heated environment may be a practical
solution for building-mounted signs or security lighting equipment.

Fluorescent lamps deliver optimal light output within a temperature
range of 21.1°C to 26.7°C (70°F to 80°F).




Above this temperature range, light output decreases by about 1%
per every two degrees Fahrenheit, making it challenging for enclosed
or recessed luminaires.
In temperatures below this range, light output decreases at a rate of 2%
per degree Fahrenheit, which can be problematic for outdoor
fluorescent lighting.
In very cold conditions, regular fluorescent lamps may not reach full
light output, but in closed fixtures or shielded from drafts, the
ambient temperature around the lamp may increase, improving light
output.
HID lamps can gradually reach normal light output when provided
with sufficient voltage in cold weather.

Ballasts designed for cold weather operation are recommended below
10 °C (50 °F).

High temperatures can affect ballast life, so proper heat dissipation is
crucial.

The ballast hum may become noticeably audible above the ambient
sound level.

Fluorescent and HID lamp ballasts are typically quiet when placed on
a vibration-resistant base, but vibrations in the luminaire itself can
cause a noticeable tonal hum.

Whether annoyance is likely to be ascribed to a lighting system
depends on the sound level.

The design and construction of the luminaire

The design and construction of the ballast

The VA rating of the luminaire and the illuminance level

Low-rise buildings of one or two stories make up over 90% of the
existing commercial and industrial buildings.

The tonal quality is determined by the distribution of sound power
among the harmonics of 120 Hz being radiated

Fluorescent lamps reach temperatures of about 105 °F (40.6 °C) for 4foot rapid-start lamps and 140 °F (60 °C) for 1500 mA fluorescent
lamps.

Lighting systems store energy and contribute to building heating by
radiating and convecting heat into the occupied space.

In multi-story buildings, lighting on the top floor and around the
perimeter of lower floors can replace heat losses throughout the
building shell.

Effective control and redistribution systems are required for useful
interior zone heat.

The ambient sound level in the area from other sources also affects
the sound level

Lighting economics is multifaceted and can be divided into several
categories:
-First costs
-Type and quality of lighting desired
-Energy costs
-Maintenance costs
-Effect on personnel

Energy surplus from redistribution can be stored in insulated water
tanks, saving energy and money.

These systems can also be used in the summer to chill water during
off-peak electric utility hours, reducing cooling requirements during
occupied times.

Considering lighting heat is important for managing cooling loads in
warm climates.

Building mechanical system designs should include allowances for
refrigeration tonnage and air or water volume.

The IEEE Gray Book Electrical Power System in Commercial Buildings
covers the topic of lighting.