Update
On
And
Other Important Sections
A Bulletin Providing:
 Important Changes to the 2002 Code
 Motor Disconnect Location
 Arc Flash Field Labeling
 Use of Overcurrent Protective Devices on Various Grounding
Schemes

Update and Commentary on Other Important Sections
 Meeting NEC Requirements for Series Rated Systems
Table Of Contents
Important Changes to the 2002 Code
110.16
240.85
430.102
Arc Flash Hazard Field Labeling
Circuit Breaker Applications
Disconnecting Means Location
2
7
16
Update and Commentary on Other Important Sections
110.22
240.86
Field Labeling Requirements for Series Combination Ratings
Requirements for use of Series Ratings
19
20
National Electrical Code ® and N.E.C. ® are registered trademarks of the National Fire Protection
Association (NFPA), Inc., Quincy, MA 02269. This bulletin does not reflect the official position of
the NFPA.
Great care has been taken to assure the recommendations herein are in accordance with the N.E.C ®
and sound engineering principles. Bussmann ® cannot take responsibility for errors or omissions that
may exist. The responsibility for compliance with the regulatory standards lies with the user.
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© 2001 Cooper Bussmann, Inc.
NEW for 2002
110.16 Flash Protection Field Marking
110.16 Flash Protection. Switchboards, panelboards, industrial control panels, and motor control
centers in other than dwelling occupancies, that are likely to require examination, adjustment, servicing,
or maintenance while energized, shall be field marked to warn qualified persons of potential electric arc
flash hazards. The marking shall be located so as to be clearly visible to qualified persons before
examination, adjustment, servicing, or maintenance of the equipment.
FPN No. 1: NFPA 70E-2000, Electrical Safety Requirements for Employee Workplaces, provides
assistance in determining severity of potential exposure, planning safe work practices, and
selecting personal protective equipment.
FPN No. 2: ANSI Z535.4-1998, Product Safety Signs and Labels, provides guidelines for the
design of safety signs and labels for application to products.
Reprinted from NEC® 2002
!
WARNING
Arc Flash and Shock Hazard
Appropriate PPE Required
Courtesy E.I. du Pont de Nemours & Co.
Figure 1: Example of warning label – this label warns of both arc flash
and shock hazards plus reminds workers to use proper PPE
(Personal Protective Equipment).
This new requirement is intended to reduce the occurrence of serious injury or death due to arcing faults
to workers who work on or near energized electrical equipment. The warning label should remind a
qualified worker who intends to open the equipment for analysis or work that a serious hazard exists and
that the worker should follow appropriate work practices and wear appropriate personal protection
equipment (PPE) for the specific hazard (a non qualified worker must not be opening the equipment).
An arcing fault is the flow of current through the air between phase conductors or phase conductors and
neutral or ground. An arcing fault can release tremendous amounts of energy at the point of the arcing
in a small fraction of a second. The result can be extremely high temperatures, a tremendous pressure
blast and shrapnel (equipment parts) hurling at high velocity (in excess of 700 miles per hour). An
accidental slip of a tool or a lose part tumbling across live parts can initiate an arcing fault in the
equipment. If a person is in the proximity of an arcing fault, the flash can cause serious injury or death.
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Figure 2 shows sequential photos of one of many staged tests that helped to understand and quantify the
effects of arcing faults on workers. In this test, mannequins with temperature and pressure sensors were
placed in the test cell. This was a 480 volt, three phase system with an available three phase shortcircuit current of 22,600 symmetrical rms amperes. A non current-limiting overcurrent protective
device was the nearest upstream protective device. An arcing fault was initiated in a combination motor
controller enclosure. The arcing fault quickly escalated into a three phase arcing fault in the enclosure.
The current flowed for 6 cycles (1/10 second). The temperature recorders (with maximum temperature
limit of 457 F) on the neck and hand of the mannequin closest to the arcing fault were pegged (beyond
457 F limit) (threshold for incurable burn is for skin to reach 205 F for 1/10 second). The pressure
sensor on this mannequin’s chest pegged the recorder at over 2160 lbs/ft2 (the threshold for severe lung
damage is 2160 lbs/ft2). This test and others are detailed in “Staged Tests Increase Awareness of ArcFault Hazards in Electrical Equipment”, IEEE Petroleum and Chemical Industry Conference Record,
September, 1997, pp. 313-322. This paper can be found on the Cooper Bussmann web site at
www.bussmann.com/services/safetybasics. One finding of this IEEE paper is that current-limiting
overcurrent protective devices reduce damage and arc-fault energy (provided the fault current is within
the current-limiting range).
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2
3
4
5
6
Figure 2: Non-Current Limiting Staged Test.
The type of equipment specified in 110.16 that is likely to be worked on as described is required to have
a field affixed arc flash warning label. This will serve as a reminder to qualified workers that a serious
hazard exists, that they or their management must assess the risk prior to approaching the hazard and
that they must follow the work practices for the level of hazard they may be working on or near.
110.16 only requires that this label state the existence of an arc flash hazard. It is suggested that the
party responsible for the label include more information on the specific parameters of the hazard. In this
way the qualified worker and his/her management can more readily assess the risk and better insure
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proper work practices, PPE and tools. The specific additional information that should be added to the
label includes:
Available Short- Circuit Current
Flash Protection Boundary
Incident energy at 18 inches expressed in cal/cm2
PPE required
Voltage shock hazard
Limited shock approach boundary
Restricted shock approach boundary
Prohibited shock approach boundary
!
WARNING
Arc Flash and Shock Hazard
Appropriate PPE Required
24 inch Flash Hazard Boundary
3
cal/cm2 Flash Hazard at 18 inches
1DF
PPE Level, 1 Layer 6 oz Nomex®,
Leather Gloves, Faceshield
480 VAC Shock Hazard when Cover is removed
36 inch Limited Approach
12 inch Restricted Approach - 500 V Class 00 Gloves
1 inch Prohibited Approach - 500 V Class 00 Gloves
Equipment Name: Slurry Pump Starter
Courtesy E.I. du Pont de Nemours & Co.
Figure 3: This example label includes more of the vital information that fosters safer work practices.
OSHA regulations state in 1910.333 (a) that workers should not work on live equipment (greater than 50
volts) except for one of two reasons (NFPA 70E Electrical Safety Requirements for Employee
Workplaces – 2000 in Part II 2-1.1.1 states essentially the same requirement):
1. Deenergizing introduces additional or increased hazards (such as cutting ventilation to a
hazardous location)
or
2. Infeasible due to equipment design or operational limitations (such as when voltage testing is
required for diagnostics ).
However, when it is necessary to work on equipment “live”, it is necessary to follow safe work
practices, which include assessing the risks, wearing adequate personal protective equipment and using
the proper tools.
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Until equipment is put into a “safe work condition” (there are procedural steps provided in NFPA 70 E
Part II 2-1.1.3) the equipment is considered to be “live”. One of the latter steps in this procedure is a
voltage test of each phase conductor to verify they are deenergized. The worker performing this voltage
testing must assume the equipment is live and therefore must wear appropriate PPE for the hazard
assessed for the specific equipment and circuit parameters.
The arc flash hazard can be assessed prior to working on equipment. Knowing the available bolted short
circuit current, the minimum sustainable arcing fault current, and the time duration for the equipment
supply overcurrent protective device to open, it is possible to calculate the Flash Protection Boundary
(FPB) and Incident Energy Exposure level. NFPA 70E provides the formulas for this critical
information as well as other important information on safe work practices, appropriate personal
protective equipment and appropriate tools to use. A qualified worker should not enter the flash
protection boundary to work on live parts unless he/she is wearing the appropriate PPE for the level of
hazard that could occur.
Equipment
Flash Protection Boundary (FPB)
Must wear appropriate PPE
FPB dependent on fault level and time duration.
Prohibited Shock Boundary: Qualified Persons Only. PPE as if direct
contact with live part
Restricted Shock Boundary: Qualified Persons Only
Limited Shock Boundary:
Qualified or Unqualified Persons*
* Only if accompanied by Qualified Person
Note: shock boundaries dependent on system voltage level
Figure 4: Graphic illustrating the flash protection boundary and the three shock protection
boundaries. The flash protection boundary can be greater than limited shock boundary.
There are viable means to reduce the risks of the shock and flash hazards. Use finger safe products that
will reduce the chance that a shock or arcing fault can occur. Use current-limiting fuses or currentlimiting circuit breakers. Current-limiting fuses or current-limiting circuit breakers can reduce the risks
associated with arc flash hazards by limiting the magnitude of the fault currents (provided the fault
current is within the current-limiting range) and reducing the time duration of the fault. Figure 5 below
is the same test setup as shown in Figure 2 except that the arcing fault is cleared by 601 ampere currentlimiting fuses. Consequently the arc flash was greatly reduced.
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© 2001 Cooper Bussmann, Inc.
1
2
4
5
3
6
Figure 5 – Current Limiting Staged Test
Compare this to Figure 2, which is the same test setup, but with noncurrent-limiting protection.
To learn more about electrical hazards and safety requirements see Bussmann Safety Basics Handbook
for Electrical Safety. Cooper Bussmann also offers a trainers kit for electrical safety training which
includes a video, handbook, electronic presentations and more – order Safety Basics Kit Part # SBK
from your local Cooper Bussmann distributor. For more information about Safety Basics visit
www.bussmann.com/services/safetybasics.
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© 2001 Cooper Bussmann, Inc.
240.85: CHANGES TO THE 2002 NEC® CLARIFY REQUIREMENTS FOR THE USE OF SLASHRATED CIRCUIT BREAKERS AND APPLICATION OF INDIVIDUAL POLE INTERRUPTING
CAPABILITIES FOR VARIOUS GROUNDING SCHEMES
Typical plant electrical systems use three-phase distribution schemes. As an industry practice, shortcircuit calculations lead to the selection of overcurrent protective devices based on available three-phase
fault currents. If the overcurrent devices have an adequate three-phase interrupting rating, engineers are
generally satisfied that the system complies with NEC 110.9.
How often, however, do three-phase faults occur? Commonly referred to as "three-phase bolted faults",
these shorts require all three legs to be electrically connected. Though bolted faults do occur, far more
common is the mishap of a slipped screwdriver, dropped wrench, or worn insulation that shorts one
phase to ground, creating a single-pole short-circuit. These phase-to-ground faults affect the
performance of circuit breakers in different ways, depending upon the grounding scheme. Two of these
performance areas were addressed by changes to the 2002 NEC. They are the proper usage of slash
ratings and individual pole interrupting capabilities. The following paragraphs explain the reasons
behind these 2002 Code changes.
SLASH RATINGS
A slash-rated circuit breaker is one with two voltage ratings separated by a slash, such as 208Y/120 volt.
The smaller of the two ratings is for overcurrents at line-to-ground voltages, meant to be cleared by one
pole of the device. The larger of the two ratings is for overcurrents at line-to-line voltages, meant to be
cleared by two or three poles of the circuit breaker. Slash-rated circuit breakers are not intended to open
phase-to-phase voltages across only one pole. Where it is possible for full phase-to-phase voltage to
appear across only one pole, a fully rated circuit breaker must be utilized. A fully rated circuit breaker is
one that has only one voltage rating, such as a 480 volt circuit breaker. For example, a 480 volt circuit
breaker can open an overcurrent at 480 volts with only one pole, such as might occur when Phase A
goes to ground on a 480 volt B-Phase grounded system.
240.85 of the 2002 NEC was changed to read:
240.85 Applications. A circuit breaker with a slash rating, such as 120/240V or 480Y/277,
shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any
conductor to ground does not exceed the lower of the two values of the circuit breaker’s voltage
rating and the nominal voltage between any two conductors does not exceed the higher value of
the circuit breaker’s voltage rating…”
Reprinted from NEC 2002
The change was the addition of the words “solidly grounded”*. This was needed to emphasize that
slash-rated devices were not appropriate on resistance-grounded and ungrounded systems. The
following paragraphs explain why slash-rated devices cannot be utilized on these types of systems.
* Solidly grounded is defined in 230.95 of the NEC® as “Connection of the grounded conductor to
ground without inserting any resistance or impedance devices.
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SINGLE-POLE INTERRUPTING CAPABILITIES
The single-pole interrupting capability of a circuit breaker is its ability to open an overcurrent at a
specified voltage utilizing only one pole of the circuit breaker. What are the single-pole interrupting
capabilities for overcurrent devices? Per ANSI C37.13 and C37.16, an airframe/power circuit breaker
has a single-pole interrupting rating of 87% of its three-pole rating. Listed three-pole molded case
circuit breakers have minimum single-pole interrupting capabilities according to Table 7.1.7.2 of UL
489. Table 1 of this paper indicates the single-pole ratings of various three-pole molded-case circuit
breakers taken from Table 7.1.7.2 of UL 489. A similar table is shown on page 54 of the IEEE “Blue
Book”, Recommended Practice for Applying Low-Voltage Circuit Breakers Used in Industrial and
Commercial Power Systems, (Std 1015-1997). Molded-case circuit breakers may or may not be able to
safely interrupt single-pole faults above these values since they are typically not tested beyond these
values. For current-limiting fuses, the marked interrupting rating is the tested single-pole interrupting
rating.
If the ratings shown in Table 1 are too low for the application, the actual single-pole rating for the
breaker must be ascertained to insure proper application.
As an example of single-pole interrupting capability in a typical installation, consider a common threepole, 20 amp, 480 volt circuit breaker with a three-pole interrupting rating of 65,000 amperes. Referring
to Table 1, this breaker has an 8,660 ampere single-pole interrupting capability for 480 volt faults across
one pole. If the available line-to-ground fault current exceeds 8,660 amps at 480 volts, such as might
occur on the secondary of a 1000 KVA, 480 volt, corner-grounded delta transformer, the circuit breaker
may be misapplied. In this case, the breaker manufacturer must be consulted to verify interrupting
ratings and proper application.
A Fine Print Note was added to 240.85 of the 2002 NEC to alert users that circuit breakers have singlepole interrupting capabilities that must be considered for proper application.
240.85 FPN: Proper application of molded case circuit breakers on 3-phase systems, other
than solidly grounded wye, particularly on corner grounded delta systems, considers the
circuit breakers’ individual pole interrupting capability.
Reprinted from NEC® 2002
The following paragraphs will also explain why this FPN was added to the 2002 NEC.
CALCULATING GROUND FAULT CURRENTS
How much short-circuit current will flow in a ground fault condition? The answer is dependent upon
the location of the fault with respect to the transformer secondary. Referring to Figure 2, the ground
fault current flows through one coil of the wye transformer secondary and through the phase conductor
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© 2001 Cooper Bussmann, Inc.
to the point of the fault. The return path is through the enclosure and conduit to the bonding jumper and
back to the secondary through the grounded neutral. Unlike three-phase faults, the impedance of the
return path must be used in determining the magnitude of ground fault current. This ground return
impedance is usually difficult to calculate. If the ground return path is relatively short (i.e. close to the
center tap of the transformer), the ground fault current will approach the three-phase short-circuit
current.
TABLE 1
Single-Pole Interrupting Ratings for Three-Pole Molded Case
Circuit Breakers (ANY I.R.)
FRAME RATING
240V
480/277V
480V
600/347V
600V
100A Maximum
250V Maximum
4,330
--
--
--
--
100A Maximum
251-600V
--
10,000
8,660
10,000
8,660
101 – 800
8,660
10,000
8,660
10,000
8,660
801 – 1200
12,120
14,000
12,120
14,000
12,120
1201 – 2000
14,000
14,000
14,000
14,000
14,000
2001 – 2500
20,000
20,000
20,000
20,000
20,000
2501 – 3000
25,000
25,000
25,000
25,000
25,000
3001 – 4000
30,000
30,000
30,000
30,000
30,000
4001 – 5000
40,000
40,000
40,000
40,000
40,000
5001 – 6000
50,000
50,000
50,000
50,000
50,000
Theoretically, a bolted line-to-ground fault may be higher than a three-phase bolted fault since the zerosequence impedance can be less than the positive sequence impedance. The ground fault location will
determine the level of short-circuit current available. The prudent design engineer assumes that the
ground fault current equals at least the available three-phase bolted fault current and makes sure that the
overcurrent devices are rated accordingly.
SOLIDLY GROUNDED WYE SYSTEMS
The Solidly Grounded Wye system shown in Figure 1 is by far the most common type of electrical
system. This system is typically delta connected on the primary and has an intentional solid connection
between the ground and the center of the wye connected secondary (neutral). The grounded neutral
conductor carries single-phase or unbalanced three-phase current. This system lends itself well to
industrial applications where 480V(L-L-L) three-phase motor loads and 277V(L-N) lighting is required.
Figure 1 - Solidly Grounded WYE
System
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If a fault occurs between any phase conductor and ground (Figure 2), the available short-circuit current
is limited only by the combined impedance of the transformer winding, the phase conductor and the
equipment ground path from the point of the fault back to the source. Some current (typically 5%) will
flow in the parallel earth ground path. Since the earth impedance is typically much greater than the
equipment ground path, current flow through earth ground is generally negligible.
Figure 2 - Single-Pole Fault to Ground Solidly
Grounded Wye System
In solidly grounded wye systems, the first low impedance fault to ground is generally sufficient to
open the overcurrent device on the faulted leg. In Figure 2, this fault current causes the branch circuit
overcurrent device to clear the 277 volt fault. Because the branch circuit device will clear the fault
with only 277 volts across one pole, a slash-rated 480Y/277 volt circuit breaker is perfectly acceptable.
This system requires compliance with single-pole interrupting capability for 277 volt faults on one
pole. If the overcurrent devices have a single-pole interrupting capability adequate for the available
short-circuit current, then the system meets NEC 110.9.
Although not as common as the solidly grounded wye connection, the following three systems are
typically found in industrial installations where continuous operation is essential. Whenever these
systems are encountered, it is absolutely essential that the proper application of slash ratings and
single-pole interrupting capabilities be assured. This is due to the fact that full phase-to-phase voltage
can appear across just one pole. Phase-to-phase voltage across one pole is much more difficult for an
overcurrent device to clear than the line-to-neutral voltage associated with the solidly grounded wye
systems.
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CORNER-GROUNDED-DELTA SYSTEMS (SOLIDLY GROUNDED)
The system of Figure 3 has a delta-connected secondary and is solidly grounded on the B-phase.
If the B-phase should short to ground, no fault current will flow because it is already solidly grounded.
Figure 3 – Corner-Grounded Delta System
(Solidly Grounded)
If either Phase A or C is shorted to ground, only one pole of the branch-circuit overcurrent device will
see the 480V fault as shown in Figure 4. A slash rated 480Y/277 volt circuit breaker could not be
utilized on this 480 volt corner-grounded delta circuit because the voltage to ground (480 volts), exceeds
the lower of the two ratings (277 volts). This system also requires compliance with single-pole
interrupting capabilities for 480 volt faults on one pole because the branch-circuit circuit breaker would
be required to interrupt 480 volts with only one pole.
Figure 4 – Fault to Ground on a CornerGrounded Delta System
A disadvantage of Corner-Grounded Delta systems is the inability to readily supply voltage levels for
fluorescent or HID lighting (277V). Installations with this system require a 480-120V transformer to
supply 120V lighting. Another disadvantage, as given on page 33 of IEEE Std 142-1991, Section
1.5.1(4) (Green Book) is " the possibility of exceeding interrupting capabilities of marginally applied
circuit breakers, because for a ground fault, the interrupting duty on the affected circuit breaker pole
exceeds the three-phase fault duty."
RESISTANCE GROUNDED SYSTEM
"Low or High" resistance grounding schemes are found primarily in industrial installations. These
systems are used to limit, to varying degrees, the amount of current that will flow in a phase to ground
fault.
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"Low" resistance grounding is used to limit ground fault current to values acceptable for relaying
schemes. This type of grounding is used mainly in medium voltage systems and is not widely installed
in low voltage applications (600V or below).
The "High" Resistance Grounded System offers the advantage that the first fault to ground will not draw
enough current to cause the overcurrent device to open. This system will reduce the stresses, voltage
dips, heating effects, etc. normally associated with high short-circuit current. Referring to Figure 5,
High Resistance Grounded Systems have a resistor between the center tap of the wye transformer and
ground.
With high resistance grounded systems, line-to-neutral
loads are not permitted per National Electrical Code,
250.36(4).
Figure 5 - Resistance Grounded System
When the first fault occurs from phase to ground as shown in Figure 6, the current path is through the
grounding resistor. Because of this inserted resistance, the fault current is not high enough to open
protective devices. This allows the plant to continue "on line". NEC 250.36(3) requires ground
detectors to be installed on these systems, so that the first fault can be found and fixed before a second
fault occurs on another phase.
Figure 6 - First Fault in Resistance Grounded
System
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Even though the system is equipped with a ground alarm, the exact location of the ground fault may be
difficult to determine. The first fault to ground MUST be removed before a second phase goes to
ground, creating a 480 volt fault across only one pole of the affected branch circuit device. Figure 7
shows how the 480 volt fault can occur across one pole of the branch circuit device. It is exactly
because of this possibility that a slash rated 480Y/277 volt device can not be used in this system. 480
volts would be impressed across one pole of the branch circuit device, even though it had been tested for
only 277 volts.
Figure 7 - Second fault in Resistance
Grounded System
The magnitude of this fault current can approach 87% of the L-L-L short-circuit current. Because of the
possibility that a second fault will occur, single-pole interrupting capability must be investigated. The
IEEE “Red Book”, Std 141-1993, page 367, supports this requirement, “One final consideration for
resistance-grounded systems is the necessity to apply overcurrent devices based upon their “single-pole”
short-circuit interrupting rating, which can be equal to or in some cases less than their ‘normal rating’.”
UNGROUNDED SYSTEMS
The Ungrounded System of Figure 8 offers the same advantage for continuity of service that is
characteristic of high resistance grounded systems.
Figure 8 –Ungrounded System
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Although not physically connected, the phase conductors are capacitively coupled to ground. The first
fault to ground is limited by the large impedance through which the current has to flow (Figure 9).
Since the fault current is reduced to such a low level, the overcurrent devices do not open and the plant
continues to "run".
Figure 9 - First Fault to Conduit in
Ungrounded System
As with High Resistance Grounded Systems, ground detectors should (but are not required by the 2002
NEC) be installed, to warn the maintenance crew to find and fix the fault before a second fault from
another phase also goes to ground (Figure 10).
Figure 10 - Second Fault to Conduit in Ungrounded
System
The second fault from Phase B to ground (in Figure 10) will create a 480 volt fault across only one pole
at the branch circuit overcurrent device. It is because of this possibility that a slash-rated device cannot
be used on this type of system. A pole that was tested for 277 volts might see an overcurrent and try to
open 480 volts.
Again, the values from Table 1 must be used for molded case circuit breaker systems as the tradeoff for
the increased continuity of service. The IEEE “Red Book”, Std 141-1993, page 366, supports this
requirement, “One final consideration for ungrounded systems is the necessity to apply overcurrent
devices based upon their “single-pole” short-circuit interrupting rating, which can be equal to or in some
cases less than their normal rating.” In 250.4(B) Ungrounded Systems (4) Path for Fault Current of the
2002 NEC®, it is required that the impedance path through the equipment be low so that the fault current
is high when a second fault occurs on an ungrounded system.
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CONCLUSIONS
Two significant additions to NEC 240.85 were included in the 2002 NEC. They cover voltage ratings
of slash-rated circuit breakers and single-pole interrupting capabilities of circuit breakers. The proper
application of both of these ratings is dependent upon the type of grounding scheme utilized.
Slash-rated devices must be utilized only on solidly grounded systems. This automatically eliminates
their usage on resistance-grounded and ungrounded systems. They can be properly utilized on solidly
grounded wye systems, where the voltage to ground does not exceed the smaller of the circuit breaker’s
two values and the voltage between any two conductors does not exceed the larger of the circuit
breaker’s two values. Slash-rated devices can not be used on corner-grounded delta systems whenever
the voltage to ground exceeds the smaller of the two ratings. Where slash-rated devices will not meet
these requirements, fully rated devices are required.
An overcurrent protective device must have an interrupting rating equal to or greater than the current
available at its line terminals for both three-phase bolted faults and for one or more phase-to-ground
faults. Although most electrical systems are designed with overcurrent devices having adequate threephase interrupting ratings, the single-pole interrupting capabilities are easily overlooked.
Simple solutions exist to provide adequate interrupting ratings if molded case circuit breaker single-pole
interrupting capabilities as shown in Table 1 are not sufficient. First, the manufacturer can be consulted
to see if single-pole interrupting capabilities are in compliance. Second, air frame/power circuit
breakers have tested single-pole interrupting ratings that are 87% of the published three-pole rating. And
third, current-limiting fuses are available that have tested single-pole interrupting ratings of 200,000 and
300,000 amps.
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NEW for 2002
430.102 Requirements For Disconnecting Means Within Sight Of Motors
Introduction
430.102 covers the requirements for the location of disconnecting means of motor circuits. 430.102(A)
covers the requirements for the controller disconnecting means, while 430.102(B) contains the
requirements for the motor disconnecting means.
1999 NEC Requirements
The basic requirement from the 1999 NEC was that a disconnecting means was required “within sight”
(visible and within 50 feet) of every motor controller (430-102(a)). A disconnecting means was also
required “within sight” of every motor, unless the disconnecting means for the controller was capable of
being locked in the off position (430-102(b) Exception).
2002 NEC Requirements
430.102(B) Motor. A disconnecting means shall be located in sight from the motor
location and the driven machinery location. The disconnecting means required in
accordance with 430.102(A) shall be permitted to serve as the disconnecting means for
the motor if it is located in sight from the motor location and the driven machinery
location.
Reprinted from NEC® 2002
In sight (of controller)
disconnecting means
ahead of controller
required per 430.102(A)
Barrier, wall or
isle with an
obstruction
In sight motor
disconnecting means
required per 430.102(B)
M
The new general rule is that a disconnecting means is required within sight of every motor, whether or
not the disconnecting means at the controller is capable of being locked in the off position. This is a
very significant change and an enormous advancement for improved worker safety.
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An example might help. Assume an MCC, with a lockable combination starter, feeds a 50 hp motor
located 500 feet from the MCC. According to the 1999 NEC, a disconnecting means was not required
within sight of the 50 hp motor because the disconnecting means for the controller, in the MCC, was
capable of being locked in the off position. A maintenance worker that was called to the motor would
have to walk the 500 feet back to the MCC to disconnect and lock off the motor circuit, and then return
500 feet to work at the motor. After the work was finished, the worker must walk 500 feet to reenergize the circuit and then walk back to the motor to check that everything is working correctly. In
situations like this, some workers have been tempted to work the equipment “hot”, rather than walk back
and forth to shut down and lock out the circuit properly.
The 2002 NEC requires that a disconnecting means be within sight of that 50 hp motor. There is much
less chance that the worker will attempt to work the equipment “hot”.
Exception under 430.102(B)
The exception, modified during the Comment period, makes allowances for situations where the
disconnecting means would be impractical or increase hazards, or where located in an industrial
installation that has written safety procedures and only qualified people can work on the equipment. A
Fine Print Note was added to give examples of increased hazards, such as very large motors, equipment
with more than one motor (most industrial machinery), submersible motors, drives, and motors for
classified areas.
Exception: The disconnecting means shall not be required to be in sight from the motor and
the driven machinery location under either condition (1) or (2) below, provided the
disconnecting means required in accordance with 430.102(A) is individually capable of
being locked in the open position. The provision for locking or adding a lock to the
disconnecting means shall be permanently installed on or at the switch or circuit breaker
used as the disconnecting means.
(1) Where such a location of the disconnecting means is impracticable or introduces
additional or increased hazards to persons or property.
(2) In industrial installations, with written safety procedures, where conditions of
maintenance and supervision ensure that only qualified persons will service the equipment.
FPN No. 1: Some examples of increased or additional hazards include, but are not
limited to: motors rated in excess of 100 hp, multi-motor equipment, submersible
motors, motors associated with variable frequency drives and motors located in
hazardous (classified) locations.”
Reprinted from NEC® 2002
Permanently installed lockout provisions
A major change was also made to the locking requirements. New wording mandates that the lock or
provisions for locking must be permanent. This was added to specifically eliminate the portable locking
devices, which are easily defeated, and those devices that can be overcome by simply removing a cover.
The type of lockout provision or fixture (not the lock) that is added onto the circuit breaker or switch at
the time of the lockout procedure is not permissible.
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© 2001 Cooper Bussmann, Inc.
Then disconnecting
means ahead of
controller must have
permanently
installed lockout
provision
Barrier, wall or
isle with an
obstruction
If in sight motor
disconnecting means
omitted per exception
M
Conclusion:
With this Code change, the general rule now requires the motor disconnecting means to be within sight
of the motor and driven machinery location. Exceptions exist for situations where the controller
disconnecting means can be locked in the off position and (1) the location is impracticable or where
hazards would be introduced, or (2) it is an industrial location with written safety procedures, and
serviced only by qualified workers. Finally, the provisions for locking must be permanently installed
(not the types that are portable, easily removed with the lock in place, or that can be defeated by just
removing the cover).
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© 2001 Cooper Bussmann, Inc.
Update on Important Requirement
110.22 Field Marking of Series Combination Ratings
110.22 and 240.86(A) require marking when a series combination rating is utilized. See Figure 1 below.
110.22 places responsibility on the installer (electrical contractor) to field install labels on the equipment
enclosures which note the short-circuit rating of the series combination and call out the specific
replacement overcurrent protective devices to be utilized. If the upstream overcurrent protective device
protecting the downstream circuit breaker is in a different enclosure, then both enclosures need to have
field-installed labels affixed. This field marking is critical to ensuring that proper devices are installed
as initially intended and years later. It becomes absolutely necessary when replacement of fuses or
circuit breakers is needed; this field marking helps ensure that the original system design is maintained.
If the wrong replacement circuit breaker is used on the loadside or lineside or the wrong fuse is used on
the lineside, the series rating is no longer valid. This could result in a serious fire and safety hazard.
See discussion in this book on 240.86(A) for additional series rated labeling requirements that are the
responsibility of the equipment manufacturer. Those requirements are meant to ensure that the
switchboard, panelboard, or loadcenter is tested, listed and marked for use with the acceptable
combination of devices being utilized. Also refer to the section in this book on 110.16 concerning field
labeling for arc flash hazards
Short-circuit calculations must be performed at panel locations where series rated combinations
systems are utilized. This is necessary to assure that the series combination rating is sufficient for the
short-circuit current available at the specific installation point.
For more information on series combination ratings and the available fuse / circuit breaker
combinations, see the discussion in this bulletin for 240.86 or visit series rated systems under
Application Information at www.Bussmann.com.
Contractor Installed Label
Panel
MDP1
CAUTION
Series Rated Combination System
with panel LDP1
Rated 100,000 Amperes
Replace with Bussmann
LPJ-200SP Fuses Only
Panel Mfr’s Label
Contractor Installed Label
CAUTION
NRTL Listing of Series
Combination Rating of
100,000 amperes when
XXX Circuit Breaker
Protected by Maximum
of 400 A Class J Fuse
Series Rated Combination System
with LPJ-200SP fuses in MDP1
Rated 100,000 Amperes
Replace with XXX
Circuit Breakers Only
Panel LDP1
Figure 1: Field labeling requirement (110.22) and manufacturer’s labeling requirement (240.86)
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© 2001 Cooper Bussmann, Inc.
Update on Important Requirement
240.86 Series Ratings
110.9 requires that overcurrent devices be able to safely interrupt whatever overcurrents they are apt to
encounter. For branch circuit fuses and circuit breakers, this means that they must safely interrupt both
overloads and short-circuits, up to the maximum available short-circuit current. There are two ways that
overcurrent protective devices can meet these short-circuit requirements. They can be fully rated or they
can be series rated.
Fully Rated System
A fully rated system is one in which all of the overcurrent protective devices have an individual
interrupting rating at least as great as the available short-circuit current at their point of application.
Fully rated systems can consist of all fuses, all circuit breakers, or a combination of fuses and circuit
breakers.
Fully Rated Systems - Fuses
LPJ-200SP
300,000 A Interrupting
Rating
LPJ-20SP
300,000 A Interrupting
Rating
I=300,000 A
Short Circuit Available
I=300,000 A
Short circuit Available
Figure 1
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© 2001 Cooper Bussmann, Inc.
Series Rated System
A series rated system is a combination of circuit breakers, or fuses and circuit breakers, that can be
applied at available short-circuit levels above the interrupting rating of the load side circuit breakers, but
not above that of the main or line-side device. Series rated systems can consist of fuses protecting
circuit breakers, or circuit breakers protecting circuit breakers. Figure 2 illustrates a fuse/circuit breaker
series rated system.
Series Rated System Fuse/CB
LPJ 400 SP
300,000 A
Interrupting Rating
Series Rated
Combination
200,000 A. IR
20A Circuit Breaker
10,000 A Interrupting
Rating
ISC=300,000 A
Short Circuit Available
I=200,000 A
Short Circuit Available
Figure 2
Fully rated systems can be used everywhere, as long as individual interrupting ratings are adequate. On
the other hand, series rated systems have limited applications and have extra NEC® requirements that
must be followed. 240.86 covers requirements for series rated systems.
Labeling Requirements
Factory labeling
240.86(A) requires that, when a series rated combination is used, the switchboards, panelboards, and
loadcenters be tested, listed and factory marked for use with the series rated combinations to be utilized.
It is the responsibility of the panelboard, switchboard and loadcenter manufacturers to have a Nationally
Recognized Testing Laboratory listing for the complete package, which includes the series rated devices
to be used in the specific gear. This is evidenced by a factory marked label affixed to the equipment –
Figure 3. Because there is often not enough room in the equipment to show all of the legitimate series
rated combinations, UL 67 (Panelboards) allows for a bulletin to be referenced and supplied with the
panelboard. The bulletin is to be affixed to the panelboard. These bulletins typically provide all of the
acceptable combinations.
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© 2001 Cooper Bussmann, Inc.
Field Labeling Requirement
Besides the factory labeling requirement of 240.86(A) mentioned in the previous paragraph,110.22
requires the installer to place labels in the field which note the short-circuit rating of the series
combination and call out for specific replacement overcurrent devices to be utilized – Figure 3. See the
110.22 discussion in this booklet on this requirement.
Contractor Installed Label
Panel
MDP1
CAUTION
Series Rated Combination System
with panel LDP1
Rated 100,000 Amperes
Replace with Bussmann
LPJ-200SP Fuses Only
Panel Mfr’s Label
Contractor Installed Label
CAUTION
NRTL Listing of Series
Combination Rating of
100,000 amperes when
XXX Circuit Breaker
Protected by Maximum
of 400 A Class J Fuse
Series Rated Combination System
with LPJ-200SP fuses in MDP1
Rated 100,000 Amperes
Replace with XXX
Circuit Breakers Only
Panel LDP1
Figure 3: Field labeling requirement 110.22 and factory labeling requirement 240.86(A)
Unfortunately, it is often difficult to determine which combinations go with which panelboards. In order
to clear the confusion, Cooper Bussmann has researched the major manufacturers’ application literature
and published the tables. These tables show, by manufacturer, the various combinations of fuses and
circuit breakers that are acceptable by panelboard type. These tables are published on
www.bussmann.com under Application Information.. Table 1 is a partial reprinting of one of these
tables.
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© 2001 Cooper Bussmann, Inc.
Table 1 Example of Available Fuse / Circuit Breaker Series Rating Tables by Manufacturer
Series Rated Combination Chart
Line Side Fuse
Load Side Circuit Breaker
I-Line Switchboard/Panelboard
Maximum
Maximum
System Voltage
SCCR
(See Notes Below)
Line Side
Fuse
Load Side
Current Rating Circuit Breaker
Amps Poles
LPN-RK
600
FH, KA, KH, LA, LH, MA, MH, MX
ALL
2, 3
JJS
600
FA
ALL
2, 3
JJS
800
FH, KA, KH, LA, LH, MA, MH, MX
ALL
2, 3
LPJ
600
FA, FH, KA, KH, LA, LH, MA, MH,
MX
ALL
2, 3
KRP-C
800
KA
ALL
2, 3
KRP-C
1200
FH, LA, LH
ALL
2, 3
KRP-C
2000
KH, MA, MH, MX
ALL
2, 3
LPN-RK
600
FH, FC, KH, KC, LA, LH, LC, LX,
MA, MH, MX, NA, NC, NX
ALL
2, 3
JJS
600
FA
ALL
2, 3
JJS
800
FH, FC, KA, KH, KC, LA, LH, LC,
LX, MA, MH, MX, NA, NC, NX
ALL
2, 3
LPJ
600
FA, FH, FC, KA, KH, KC, LA, LH,
LC, LX, MA, MH, MX, NA, NC, NX
ALL
2, 3
KRP-C
800
FH, LA, LH
ALL
2, 3
KRP-C
1200
FC, KH, KC, LC, LX, MA, MH, MX
ALL
2, 3
KRP-C
2000
NA, NC, NX
ALL
2, 3
100kA
240 Vac
Max Fuse
200kA
NOTE (1): The data in these charts was compiled from information in Square D, Series Rating Data Bulletin No.
2700DB9901 and Square D Digest 171. Cooper Bussmann assumes no responsibility for the accuracy or
reliability of the information. The information contained in the tables may change without notice due to
equipment design modifications.
NOTE (2): The line-side fused switch may be in a separate enclosure or in the same enclosure as the load-side
circuit breaker. A line-side fused switch may be integral or remote.
NOTE (3): Max fuse current rating denotes the largest amperage fuse that may be used for that series rated
combination. A lower amperage fuse may be substituted for the listed fuse.
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© 2001 Cooper Bussmann, Inc.
Motor contribution limitations
One critical requirement limits the use of series rated systems, where motors are connected between the
line-side (protecting) device and the load-side (protected) circuit breaker. 240.86(B) requires that series
ratings shall not be used where the sum of motor full load currents exceeds 1% of the interrupting rating
of the load-side (protected) circuit breaker. An application of this type would provide added short
circuit current, via the motors contributing to a fault, in excess of what the load side (protected) circuit
breaker was tested to handle. Example in Figure 4.
Series Rated Systems
This does not
comply with NEC
240.86(B)
Series Rated
Combination
22,000 A. I.R.
Motor Contribution
10,000 A. I.R.
Motor F.L.A. > 100A (1% IR)
Figure 4 – Example of violation of 240.86(B) due to motor contributions.
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© 2001 Cooper Bussmann, Inc.
Other limitations
The biggest disadvantage of a series rated system is that, by definition, the line side (protecting) device
must open at the same time, and in conjunction with the load side (protected) circuit breaker. This
means that the entire panel loses power because the device feeding the panel must open under medium
to high-level short circuit conditions – Figure 5. As a result, series rated systems should not be used in
health care facilities (517-17), continuous process industrials, computer rooms, emergency circuits (70025 FPN), elevator circuits (620-62), main switchgear, or critical distribution panels. On the other hand,
fully rated systems can be selectively coordinated so that only the device closest to the short circuit
opens, leaving the rest of the system up and running.
Figure 5 – Example of lack of selective coordination inherent in series rated systems
Another disadvantage of the series rated system is the likely possibility of future expansions or system
upgrades, where the new available short-circuit current exceeds the series rating. The typical solution at
that point is to tear out the existing series rated panel and replace it with a new, properly rated one.
A more complete discussion of series rated systems and the fuse / circuit breaker series rated tables by
manufacturer are on www.bussmann.com under Application Information.
Inspection Form
In order to help in meeting the multitude of NEC requirements surrounding the use of series rated
combinations, Bussmann has created an inspection form. This form can be filled out by the installer and
verified by the inspector. The form provides a compliance checklist and background information, on the
reverse side, on the various NEC requirements. This form is available on the Bussmann website at
www.bussmann.com.
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© 2001 Cooper Bussmann, Inc.
INSPECTION FORM:
ISSUED BY:
Series Ratings
________________________________________________
________________________________________________
________________________________________________
This form provides documentation to assure compliance with the following National Electrical Code  sections on
the use of Series Rated Systems.


NFPA 70, NEC 2002, Section 110.22
NFPA 70, NEC 2002, Section 240.86
JOB #:
NAME:
LOCATION:
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
CONTRACTOR:
_________________________________________________
_________________________________________________
_________________________________________________
ESSENTIAL INFORMATION:
Load Side Panel Designation
Load Side Circuit Breaker Part Number
Load Side Circuit Breaker Interrupting Rating
Line Side Panel Designation (If applicable)
Line Side Overcurrent Protective Device Part Number
Line Side Overcurrent Protective Device Interrupting Rating
Available Short Circuit Current
Series Combination Short Circuit Rating
Compliance Checklist (For further information see discussion on reverse side for each item)
1. Manufacturer’s Label
Are both devices in use for the series rated combination marked on the end use equipment (or contained
in a booklet affixed to the equipment) as required in 240.86(A)?
YES
NO
2. Field Installed Label
Is the field label, required by 110.22, installed on all the end use equipment containing the devices used
in the series rated combination with proper identification of the replacement parts, panel locations, and
series combination short circuit rating?
YES
NO
3. Motor Contributions
If motors are connected between the series rated devices, is the combined motor full load current less
than 1% of the downstream circuit breakers’ interrupting rating?
YES
NO
4. Selective Coordination
Series rated systems should not be used in health care facilities (NEC 517.17), emergency systems
(NEC 700.25 FPN), or elevator circuits which contain more than one elevator (NEC 620.62). Is this
series rated system being installed per these requirements?
YES
NO
AN ANSWER OF NO TO ANY OF THESE QUESTION IS EVIDENCE OF LACK OF COMPLIANCE.
LACK OF SUBMITTALS IS CONSIDERED AS EVIDENCE OF LACK OF COMPLIANCE.
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© 2001 Cooper Bussmann, Inc.
Series Rated Systems
What is a Series Rated Combination:
A combination of two devices, that have been tested under specific test conditions, that work together to clear a fault. The
allowed combinations are limited to those that have been selected by the circuit breaker manufacturer for testing. Only tested
combinations can be used.
Why is a Series Rated Combination used?
A series rated system allows a load side circuit breaker to be applied in a system where the available short circuit current
exceeds the interrupting rating marked on that circuit breaker.
BACKGROUND TO CHECKLIST ITEMS
1) Manufacturer’s Label
Since the use of series rated systems is limited to specific
combinations that have been tested, the end use equipment is
required to be marked, by the manufacturer, per 240.86(A) of
the 2002 National Electrical Code. Since there are hundreds
of combinations, this marking may be in a book that is affixed
to the end use equipment, as allowed in UL67. The
manufacturer’s marking is used to verify that both devices are
part of a recognized series rated combination, the panelboard is
listed for use with the combination, and that the series
combination interrupting rating is sufficient for the available
short circuit current. This label also provides guidance for
future upgrades as to the specific replacement devices that are
allowed.
2) Field Installed Label
110.22 of the 2002 National Electrical Code requires the
installer to apply a field caution label warning that a series rated combination is being used. This label must be applied
on the panel containing the series rated combination or on both pieces of electrical equipment if the line side device is
located separate from the load side circuit breaker to assure that the proper devices have been installed and that proper
future replacements are made. The inspector can check the devices noted on the field label required by 110.22 against
the recognized combinations tested by the manufacturer and marked per 240.86.
3) Motor Contribution
A series rated combination is evaluated under specific testing
conditions of which motor contribution is not a part of the
criteria. If a motor is connected in the middle of the
combination, it would supply extra fault current that did not
exist when the combination was tested.
240.86(B) of the 2002 National Electrical Code addresses this
by restricting the use of series rated combinations when the sum
of the full load current of the motors exceeds 1% of the LOAD
SIDE circuit breaker’s interrupting rating. For example, if the
load side circuit breaker is rated 10,000 A.I.R., with motor loads
exceeding 100 amps, then a series rated combination could not
be used.
4) Selective Coordination
The biggest disadvantage of a series rated system is that, by definition, the line side (protecting) device must open at the
same time, and in conjunction with, the load side (protected) circuit breaker. This means that the panel loses power
because the device feeding the panel must open under medium to high level short circuit conditions. As a result, series
rated systems should not be used in health care facilities (NEC517.17), emergency systems (NEC700.25 FPN) and
elevator circuits which contain more than one elevator (NEC620.62).
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© 2001 Cooper Bussmann, Inc.
NOTES:
28
© 2001 Cooper Bussmann, Inc.
The Bussmann Power Module
The all-in-one Bussmann Power Module takes the confusion
and headaches out of designing and building shunt trip
disconnect capabilities into an elevator power system. It
helps meet the NEC, ANSI A17.1, and NFPA72. It’s THE
solution for industry codes and end-user requirements.
For information on the Bussmann Power Module go to
the product information section of www.bussmann.com
and select Power Module
Build a Safer Workplace With Safety BASICs
This comprehensive safety program from Cooper Bussmann
includes an instructive video, a handbook, and a CD that
guide you through safety-related codes and standards, and
literature on selecting “finger safe” devices. Equipment can
be replaced after a severe electrical accident but people can’t
be.
For information on the Bussmann Safety BASICs
program go to www.bussmann.com and select the Safety
Basics link on the home page.
Exciting New On-Line Training from Cooper Bussmann:
Cooper Bussmann is pleased to announce on-line training for important code
requirements and 2002 code changes. On October 31, 2001 Cooper Bussmann will
launch an on-line, interactive training module covering important code requirements and
changes to the 2002 code on the Cooper Bussmann website at www.bussmann.com. Come
visit us.
Contact Cooper Bussmann At:
Corporate Headquarters
Cooper Industries
Bussmann Division
P.O. Box 14460
St. Louis, Missouri 63178-4460, USA
Telephone: 314 394 2877
Facsimile: 800 544 2570
www.bussmann.com
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© 2001 Cooper Bussmann, Inc.