A Bulletin Providing: Important Changes to the 2002 Code Motor Disconnect Location Arc Flash Field Labeling Use of Overcurrent Protective Devices on

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1 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

2 Table Of Contents Important Changes to the 2002 Code Arc Flash Hazard Field Labeling Circuit Breaker Applications Disconnecting Means Location 16 Update and Commentary on Other Important Sections Field Labeling Requirements for Series Combination Ratings Requirements for use of Series Ratings 20 National Electrical Code and N.E.C. are registered trademarks of the National Fire Protection Association (NFPA), Inc., Quincy, MA 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. 1

3 NEW for Flash Protection Field Marking 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 Z , 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. 2

4 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/ft 2 (the threshold for severe lung damage is 2160 lbs/ft 2 ). This test and others are detailed in Staged Tests Increase Awareness of Arc- Fault Hazards in Electrical Equipment, IEEE Petroleum and Chemical Industry Conference Record, September, 1997, pp This paper can be found on the Cooper Bussmann web site at 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) Figure 2: Non-Current Limiting Staged Test. The type of equipment specified in 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 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 3

5 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/cm 2 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/cm 2 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 V Class 00 Gloves 1 inch Prohibited Approach 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 (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 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. 4

6 Until equipment is put into a safe work condition (there are procedural steps provided in NFPA 70 E Part II ) 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. Flash Protection Boundary (FPB) Must wear appropriate PPE FPB dependent on fault level and time duration. Equipment 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. 5

7 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 6

8 240.85: CHANGES TO THE 2002 NEC CLARIFY REQUIREMENTS FOR THE USE OF SLASH- RATED 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 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 of the 2002 NEC was changed to read: 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 of the NEC as Connection of the grounded conductor to ground without inserting any resistance or impedance devices. 7

9 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 of UL 489. Table 1 of this paper indicates the single-pole ratings of various three-pole molded-case circuit breakers taken from Table 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 ). 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 of the 2002 NEC to alert users that circuit breakers have singlepole interrupting capabilities that must be considered for proper application 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 8

10 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 100A Maximum V 4, ,000 8,660 10,000 8, ,660 10,000 8,660 10,000 8, ,120 14,000 12,120 14,000 12, ,000 14,000 14,000 14,000 14, ,000 20,000 20,000 20,000 20, ,000 25,000 25,000 25,000 25, ,000 30,000 30,000 30,000 30, ,000 40,000 40,000 40,000 40, ,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 9

11 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 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. 10

12 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 Corner- Grounded 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 V transformer to supply 120V lighting. Another disadvantage, as given on page 33 of IEEE Std , 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. 11

13 "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, (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 (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 12

14 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 , 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 13

15 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 , 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. 14

16 CONCLUSIONS Two significant additions to NEC 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. 15

17 NEW for Requirements For Disconnecting Means Within Sight Of Motors Introduction covers the requirements for the location of disconnecting means of motor circuits (A) covers the requirements for the controller disconnecting means, while (B) contains the requirements for the motor disconnecting means 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 ( (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 ( (b) Exception) NEC Requirements (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 (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 (A) Barrier, wall or isle with an obstruction In sight motor disconnecting means required per (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. 16

18 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 (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 (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. 17

19 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). 18

20 Update on Important Requirement Field Marking of Series Combination Ratings and (A) require marking when a series combination rating is utilized. See Figure 1 below 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 (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 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 or visit series rated systems under Application Information at Contractor Installed Label Panel MDP1 CAUTION Series Rated Combination System with panel LDP1 Rated 100,000 Amperes Replace with Bussmann LPJ-200SP Fuses Only Contractor Installed Label CAUTION Series Rated Combination System with LPJ-200SP fuses in MDP1 Rated 100,000 Amperes Replace with XXX Circuit Breakers Only Panel Mfr s Label NRTL Listing of Series Combination Rating of 100,000 amperes when XXX Circuit Breaker Protected by Maximum of 400 A Class J Fuse Panel LDP1 Figure 1: Field labeling requirement (110.22) and manufacturer s labeling requirement (240.86) 19

21 Update on Important Requirement Series Ratings 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 20

22 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 I SC =300,000 A Short Circuit Available Figure 2 I=200,000 A Short Circuit Available 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 covers requirements for series rated systems. Labeling Requirements Factory labeling (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. 21

23 Field Labeling Requirement Besides the factory labeling requirement of (A) mentioned in the previous paragraph, 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 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 Contractor Installed Label CAUTION Series Rated Combination System with LPJ-200SP fuses in MDP1 Rated 100,000 Amperes Replace with XXX Circuit Breakers Only Panel Mfr s Label NRTL Listing of Series Combination Rating of 100,000 amperes when XXX Circuit Breaker Protected by Maximum of 400 A Class J Fuse Panel LDP1 Figure 3: Field labeling requirement and factory labeling requirement (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 under Application Information.. Table 1 is a partial reprinting of one of these tables. 22

24 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 (See Notes Below) Maximum Maximum Line Side Max Fuse Load Side System Voltage SCCR Fuse Current Rating Circuit Breaker Amps Poles 240 Vac 100kA 200kA 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 LPJ 600 FH, FC, KA, KH, KC, LA, LH, LC, LX, MA, MH, MX, NA, NC, NX FA, FH, FC, KA, KH, KC, LA, LH, LC, LX, MA, MH, MX, NA, NC, NX ALL 2, 3 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 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. 23

25 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 (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 Series Rated Combination 22,000 A. I.R. This does not comply with NEC (B) Motor Contribution 10,000 A. I.R. Motor F.L.A. > 100A (1% IR) Figure 4 Example of violation of (B) due to motor contributions. 24

26 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 ( 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 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 25

27 INSPECTION FORM: Series Ratings ISSUED BY: 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 NFPA 70, NEC 2002, Section 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 (A)? YES NO 2. Field Installed Label Is the field label, required by , 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 ), emergency systems (NEC FPN), or elevator circuits which contain more than one elevator (NEC ). 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. 26

28 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 (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 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 against the recognized combinations tested by the manufacturer and marked per ) 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 (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 ), emergency systems (NEC FPN) and elevator circuits which contain more than one elevator (NEC ). 27

29 NOTES: 28

30 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 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 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 Come visit us. Contact Cooper Bussmann At: Corporate Headquarters Cooper Industries Bussmann Division P.O. Box St. Louis, Missouri , USA Telephone: Facsimile: