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A NEMA Industrial Automation Control Products and Systems (01IS) Section Document ICS 10-2015, Part 4
Guide to Application of Low-voltage Automatic Transfer Switch Equipment
Published by: National Electrical Manufacturers Association th 1300 North 17 Street, Suite 900 Rosslyn, Virginia 22209 www.nema.org
© 2015 National Electrical Manufacturers Association. All rights, including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the International and Pan American copyright conventions.
NEMA ICS 10-2015, Part 4 Page 2
®
Section 110.9 of NFPA 70, the National Electrical Code (NEC) requires that equipment intended to interrupt current at varying fault levels shall have an interrupting rating (IR) that is sufficient for nominal circuit voltage and the current that is available at the line terminals of the equipment. NEC Section 110.10 requires that overcurrent protective devices be selected and applied to prevent extensive damage to a circuit’s electrical components during a fault condition, such as transfer switches. Proper selection of protective devices has always been important; with changes to the NEC to more explicitly require selectivity, product information and markings have received more scrutiny. In response, the standards committees responsible for transfer switches have revised the labeling requirements for devices listed to the harmonized North American standard known in the US as UL 1008, in Canada as C22.2 No. 178.1, and in Mexico as ANCE NMX-J-672. These new labeling requirements affect all products marked as a “transfer switch,” whether automatic for emergency use, automatic for optional use, or manual. A transfer switch with integral overcurrent protection, whether a circuit breaker or a fuse, states its shortcircuit withstand/closing rating based on the integral protection. Therefore, these devices did not require marking changes. A transfer switch without integral overcurrent protection must, of course, be protected. It might be protected by fuses or by specific circuit breakers, according to its markings, which is current practice. The first new aspect is that the transfer switch may be marked as having a rating at a certain current level and time duration. For example, 42 kA at 600 V for 0.05 seconds. The time duration is in seconds to align with the time-current curves from circuit breaker manufacturers. To properly apply the transfer switch, the operating time of the protective device must be the same as or faster than the time rating of the transfer switch. In addition to short-circuit current and time rating, a transfer switch will be marked with a short-time rating, or will be marked as not having a short-time rating. This change is in response to concerns that lowvoltage power circuit breakers or insulated case circuit breakers might have the instantaneous trip disabled in the field and not properly protect a transfer switch that does not have a short-time rating. These new markings first went into effect in August 2014. Users and inspectors should expect to see the new markings over the next year. These new markings apply in Canada and Mexico also, because the requirements are in the tri-nationally harmonized standard. The following example markings are copied from the product standard UL 1008/CSA C22.2 No. 178-1/ NMX-J-672 ANCE, Transfer Switch Equipment. It is instructive to compare the different markings, since each one is related to a different kind of qualification.
© 2015 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 3
Example for a device with short-circuit but not short-time current ratings, with integral overcurrent protection. SHORT-CIRCUIT WITHSTAND AND CLOSING RATINGS
THIS TRANSFER SWITCH IS SUITABLE FOR USE IN A CIRCUIT CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT FOR THE MAXIMUM VOLTAGE MARKED BELOW.
WHEN PROTECTED BY A CIRCUIT BREAKER, IT SHALL NOT INCLUDE A SHORT-TIME TRIP RESPONSE.
SHORT-CIRCUIT CURRENT
VOLTAGE
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
65
240
50
480
42
600
SHORT-TIME CURRENT RATINGS
THIS TRANSFER SWITCH DOES NOT INCLUDE SHORT-TIME CURRENT RATINGS
© 2015 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 4
Example for a device with short-circuit and short-time current ratings, with integral overcurrent protection. SHORT-CIRCUIT WITHSTAND/CLOSING AND SHORT-TIME CURRENT RATINGS
THIS TRANSFER SWITCH IS SUITABLE FOR USE IN A CIRCUIT CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT FOR THE MAXIMUM VOLTAGE MARKED BELOW.
WHEN PROTECTED BY A CIRCUIT BREAKER WITH A SHORT-TIME TRIP RESPONSE, THE SHORTTIME RESPONSE OF THE CIRCUIT BREAKER MUST BE COORDINATED WITH THE SHORT-TIME CURRENT RATING OF THE TRANSFER SWITCH AS MARKED BELOW.
SHORT-CIRCUIT CURRENT
VOLTAGE
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
65
240
50
480
42
600
SHORT-TIME CURRENT
VOLTAGE
TIME DURATION
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
(Sec, MAXIMUM)
20
480
0.5
35
480
0.3
© 2105 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 5
Example for a device with short-circuit but not short-time current ratings, protected by an external circuit breaker. SHORT-CIRCUIT WITHSTAND AND CLOSING RATINGS
WHEN PROTECTED BY A CIRCUIT BREAKER, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN A CIRCUIT CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT FOR THE MAXIMUM TIME DURATION AND VOLTAGE MARKED BELOW.
THE CIRCUIT BREAKER MUST INCLUDE AN INSTANTANEOUS TRIP RESPONSE AND SHALL NOT INCLUDE A SHORT-TIME TRIP RESPONSE.
THE MAXIMUM CLEARING TIME OF THE INSTANTANEOUS TRIP RESPONSE MUST BE EQUAL TO OR LESS THAN THE TIME DURATION SHOWN FOR THE MARKED SHORT-CIRCUIT CURRENT.
SHORT-CIRCUIT CURRENT
VOLTAGE
TIME DURATION
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
(Sec, MAXIMUM)
65
240
0.050
50
480
0.050
42
600
0.050
35
480
0.067
SHORT-TIME CURRENT RATINGS
THIS TRANSFER SWITCH DOES NOT INCLUDE SHORT-TIME CURRENT RATINGS
© 2015 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 6
Example for a device that specifies particular circuit breakers to be used for external protection. This one has short-circuit but not short-time current ratings. SPECIFIC CIRCUIT BREAKER MANUFACTURER AND TYPE LISTING
WHEN PROTECTED BY A CIRCUIT BREAKER OF THE SPECIFIC MANUFACTURE, TYPE, AND AMPERE RATING AS MARKED BELOW, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN CIRCUITS CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT AT THE MAXIMUM VOLTAGE MARKED.
SHORT-CIRCUIT CURRENT
VOLTAGE
MANUFACTURER
TYPE
RATING
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
65
480
MFG. A
X1
1600
65
480
MFG. B
A1
1600
(AMPERES)
© 2105 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 7
Example for a device where circuit breakers are to be used for external protection. This one has shortcircuit and also short-time current ratings. SHORT-CIRCUIT WITHSTAND/CLOSING AND SHORT-TIME CURRENT RATINGS
WHEN PROTECTED BY A CIRCUIT BREAKER, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN A CIRCUIT CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT FOR THE MAXIMUM TIME DURATION AND VOLTAGE MARKED BELOW.
THE CIRCUIT BREAKER MUST INCLUDE AN INSTANTANEOUS TRIP RESPONSE UNLESS THE AVAILABLE SHORT-CIRCUIT CURRENT IS LESS THAN OR EQUAL TO THE SHORT-TIME RATING OF THE TRANSFER SWITCH AND THE CIRCUIT BREAKER INCLUDES A SHORT-TIME TRIP RESPONSE.
THE MAXIMUM CLEARING TIME OF THE INSTANTANEOUS TRIP RESPONSE MUST BE LESS THAN OR EQUAL TO THE TIME DURATION SHOWN FOR THE MARKED SHORT-CIRCUIT CURRENT.
WHEN PROTECTED BY A CIRCUIT BREAKER WITH A SHORT-TIME TRIP RESPONSE, THE SHORTTIME RESPONSE OF THE CIRCUIT BREAKER MUST BE COORDINATED WITH THE SHORT-TIME CURRENT RATING OF THE TRANSFER SWITCH AS MARKED BELOW.
SHORT-CIRCUIT CURRENT
VOLTAGE
TIME DURATION
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
(Sec, MAXIMUM)
65
240
0.050
50
480
0.050
42
600
0.050
35
480
0.067
SHORT-CIRCUIT CURRENT
VOLTAGE
TIME DURATION
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
(Sec, MAXIMUM)
20
480
0.5
35
480
0.3
© 2015 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 8
Example for a device that specifies particular circuit breakers to be used for external protection. This one has short-circuit and short-time current ratings. SPECIFIC CIRCUIT BREAKER MANUFACTURER AND TYPE LISTING AND SHORT-TIME CURRENT RATINGS WHEN USING SPECIFIC CIRCUIT BREAKERS
WHEN PROTECTED BY A CIRCUIT BREAKER OF THE SPECIFIC MANUFACTURER, TYPE, AND AMPERE RATING AS MARKED BELOW, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN CIRCUITS CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT AT THE MAXIMUM VOLTAGE MARKED AS SHOWN BELOW.
WHEN THE CIRCUIT BREAKER HAS A SHORT-TIME RESPONSE, IT SHALL BE COORDINATED WITH THE SHORT-TIME CURRENT RATING OF THE TRANSFER SWITCH SHOWN BELOW.
SHORT-CIRCUIT CURRENT
VOLTAGE
MANUFACTURER
TYPE
RATING
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
65
480
MFG. A
X1
1600
65
480
MFG. B
A1
1600
SHORT-TIME CURRENT
VOLTAGE
TIME DURATION
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
(Sec, MAXIMUM)
20
480
0.5
35
480
0.3
(AMPERES)
© 2105 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 9
Example for a device to be protected by fuses at 10 kA or less. SPECIFIC FUSE MANUFACTURER AND TYPE LISTING
WHEN PROTECTED BY A FUSE OF THE SPECIFIC MANUFACTURER, TYPE, AND AMPERE RATING AS MARKED BELOW, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN CIRCUITS CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT AT THE MAXIMUM VOLTAGE MARKED.
SHORT-CIRCUIT CURRENT
VOLTAGE
RATING
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
MANUFACTURER
TYPE
(AMPERES)
10
480
MFG. A
F1
1500
10
480
MFG. B
F2
1500
Example for device to be protected by fuses above 10kA. SHORT-CIRCUIT WITHSTAND/CLOSING RATING WHEN PROTECTED BY FUSES
WHEN PROTECTED BY A FUSE OF THE SPECIFIC FUSE CLASS AND MAXIMUM AMPERE RATING AS MARKED BELOW, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN A CIRCUIT CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT AT THE MAXIMUM VOLTAGE MARKED.
SHORT-CIRCUIT CURRENT
VOLTAGE
FUSE CLASS
RATING
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
65
480
J
1600
65
480
L
2000
(AMPERES)
§
© 2015 National Electrical Manufacturers Association
Guide to Application of Low-voltage Automatic Transfer Switch Equipment
Published by: National Electrical Manufacturers Association th 1300 North 17 Street, Suite 900 Rosslyn, Virginia 22209 www.nema.org
© 2015 National Electrical Manufacturers Association. All rights, including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the International and Pan American copyright conventions.
NEMA ICS 10-2015, Part 4 Page 2
®
Section 110.9 of NFPA 70, the National Electrical Code (NEC) requires that equipment intended to interrupt current at varying fault levels shall have an interrupting rating (IR) that is sufficient for nominal circuit voltage and the current that is available at the line terminals of the equipment. NEC Section 110.10 requires that overcurrent protective devices be selected and applied to prevent extensive damage to a circuit’s electrical components during a fault condition, such as transfer switches. Proper selection of protective devices has always been important; with changes to the NEC to more explicitly require selectivity, product information and markings have received more scrutiny. In response, the standards committees responsible for transfer switches have revised the labeling requirements for devices listed to the harmonized North American standard known in the US as UL 1008, in Canada as C22.2 No. 178.1, and in Mexico as ANCE NMX-J-672. These new labeling requirements affect all products marked as a “transfer switch,” whether automatic for emergency use, automatic for optional use, or manual. A transfer switch with integral overcurrent protection, whether a circuit breaker or a fuse, states its shortcircuit withstand/closing rating based on the integral protection. Therefore, these devices did not require marking changes. A transfer switch without integral overcurrent protection must, of course, be protected. It might be protected by fuses or by specific circuit breakers, according to its markings, which is current practice. The first new aspect is that the transfer switch may be marked as having a rating at a certain current level and time duration. For example, 42 kA at 600 V for 0.05 seconds. The time duration is in seconds to align with the time-current curves from circuit breaker manufacturers. To properly apply the transfer switch, the operating time of the protective device must be the same as or faster than the time rating of the transfer switch. In addition to short-circuit current and time rating, a transfer switch will be marked with a short-time rating, or will be marked as not having a short-time rating. This change is in response to concerns that lowvoltage power circuit breakers or insulated case circuit breakers might have the instantaneous trip disabled in the field and not properly protect a transfer switch that does not have a short-time rating. These new markings first went into effect in August 2014. Users and inspectors should expect to see the new markings over the next year. These new markings apply in Canada and Mexico also, because the requirements are in the tri-nationally harmonized standard. The following example markings are copied from the product standard UL 1008/CSA C22.2 No. 178-1/ NMX-J-672 ANCE, Transfer Switch Equipment. It is instructive to compare the different markings, since each one is related to a different kind of qualification.
© 2015 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 3
Example for a device with short-circuit but not short-time current ratings, with integral overcurrent protection. SHORT-CIRCUIT WITHSTAND AND CLOSING RATINGS
THIS TRANSFER SWITCH IS SUITABLE FOR USE IN A CIRCUIT CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT FOR THE MAXIMUM VOLTAGE MARKED BELOW.
WHEN PROTECTED BY A CIRCUIT BREAKER, IT SHALL NOT INCLUDE A SHORT-TIME TRIP RESPONSE.
SHORT-CIRCUIT CURRENT
VOLTAGE
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
65
240
50
480
42
600
SHORT-TIME CURRENT RATINGS
THIS TRANSFER SWITCH DOES NOT INCLUDE SHORT-TIME CURRENT RATINGS
© 2015 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 4
Example for a device with short-circuit and short-time current ratings, with integral overcurrent protection. SHORT-CIRCUIT WITHSTAND/CLOSING AND SHORT-TIME CURRENT RATINGS
THIS TRANSFER SWITCH IS SUITABLE FOR USE IN A CIRCUIT CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT FOR THE MAXIMUM VOLTAGE MARKED BELOW.
WHEN PROTECTED BY A CIRCUIT BREAKER WITH A SHORT-TIME TRIP RESPONSE, THE SHORTTIME RESPONSE OF THE CIRCUIT BREAKER MUST BE COORDINATED WITH THE SHORT-TIME CURRENT RATING OF THE TRANSFER SWITCH AS MARKED BELOW.
SHORT-CIRCUIT CURRENT
VOLTAGE
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
65
240
50
480
42
600
SHORT-TIME CURRENT
VOLTAGE
TIME DURATION
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
(Sec, MAXIMUM)
20
480
0.5
35
480
0.3
© 2105 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 5
Example for a device with short-circuit but not short-time current ratings, protected by an external circuit breaker. SHORT-CIRCUIT WITHSTAND AND CLOSING RATINGS
WHEN PROTECTED BY A CIRCUIT BREAKER, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN A CIRCUIT CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT FOR THE MAXIMUM TIME DURATION AND VOLTAGE MARKED BELOW.
THE CIRCUIT BREAKER MUST INCLUDE AN INSTANTANEOUS TRIP RESPONSE AND SHALL NOT INCLUDE A SHORT-TIME TRIP RESPONSE.
THE MAXIMUM CLEARING TIME OF THE INSTANTANEOUS TRIP RESPONSE MUST BE EQUAL TO OR LESS THAN THE TIME DURATION SHOWN FOR THE MARKED SHORT-CIRCUIT CURRENT.
SHORT-CIRCUIT CURRENT
VOLTAGE
TIME DURATION
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
(Sec, MAXIMUM)
65
240
0.050
50
480
0.050
42
600
0.050
35
480
0.067
SHORT-TIME CURRENT RATINGS
THIS TRANSFER SWITCH DOES NOT INCLUDE SHORT-TIME CURRENT RATINGS
© 2015 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 6
Example for a device that specifies particular circuit breakers to be used for external protection. This one has short-circuit but not short-time current ratings. SPECIFIC CIRCUIT BREAKER MANUFACTURER AND TYPE LISTING
WHEN PROTECTED BY A CIRCUIT BREAKER OF THE SPECIFIC MANUFACTURE, TYPE, AND AMPERE RATING AS MARKED BELOW, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN CIRCUITS CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT AT THE MAXIMUM VOLTAGE MARKED.
SHORT-CIRCUIT CURRENT
VOLTAGE
MANUFACTURER
TYPE
RATING
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
65
480
MFG. A
X1
1600
65
480
MFG. B
A1
1600
(AMPERES)
© 2105 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 7
Example for a device where circuit breakers are to be used for external protection. This one has shortcircuit and also short-time current ratings. SHORT-CIRCUIT WITHSTAND/CLOSING AND SHORT-TIME CURRENT RATINGS
WHEN PROTECTED BY A CIRCUIT BREAKER, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN A CIRCUIT CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT FOR THE MAXIMUM TIME DURATION AND VOLTAGE MARKED BELOW.
THE CIRCUIT BREAKER MUST INCLUDE AN INSTANTANEOUS TRIP RESPONSE UNLESS THE AVAILABLE SHORT-CIRCUIT CURRENT IS LESS THAN OR EQUAL TO THE SHORT-TIME RATING OF THE TRANSFER SWITCH AND THE CIRCUIT BREAKER INCLUDES A SHORT-TIME TRIP RESPONSE.
THE MAXIMUM CLEARING TIME OF THE INSTANTANEOUS TRIP RESPONSE MUST BE LESS THAN OR EQUAL TO THE TIME DURATION SHOWN FOR THE MARKED SHORT-CIRCUIT CURRENT.
WHEN PROTECTED BY A CIRCUIT BREAKER WITH A SHORT-TIME TRIP RESPONSE, THE SHORTTIME RESPONSE OF THE CIRCUIT BREAKER MUST BE COORDINATED WITH THE SHORT-TIME CURRENT RATING OF THE TRANSFER SWITCH AS MARKED BELOW.
SHORT-CIRCUIT CURRENT
VOLTAGE
TIME DURATION
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
(Sec, MAXIMUM)
65
240
0.050
50
480
0.050
42
600
0.050
35
480
0.067
SHORT-CIRCUIT CURRENT
VOLTAGE
TIME DURATION
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
(Sec, MAXIMUM)
20
480
0.5
35
480
0.3
© 2015 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 8
Example for a device that specifies particular circuit breakers to be used for external protection. This one has short-circuit and short-time current ratings. SPECIFIC CIRCUIT BREAKER MANUFACTURER AND TYPE LISTING AND SHORT-TIME CURRENT RATINGS WHEN USING SPECIFIC CIRCUIT BREAKERS
WHEN PROTECTED BY A CIRCUIT BREAKER OF THE SPECIFIC MANUFACTURER, TYPE, AND AMPERE RATING AS MARKED BELOW, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN CIRCUITS CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT AT THE MAXIMUM VOLTAGE MARKED AS SHOWN BELOW.
WHEN THE CIRCUIT BREAKER HAS A SHORT-TIME RESPONSE, IT SHALL BE COORDINATED WITH THE SHORT-TIME CURRENT RATING OF THE TRANSFER SWITCH SHOWN BELOW.
SHORT-CIRCUIT CURRENT
VOLTAGE
MANUFACTURER
TYPE
RATING
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
65
480
MFG. A
X1
1600
65
480
MFG. B
A1
1600
SHORT-TIME CURRENT
VOLTAGE
TIME DURATION
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
(Sec, MAXIMUM)
20
480
0.5
35
480
0.3
(AMPERES)
© 2105 National Electrical Manufacturers Association
NEMA ICS 10-2015, Part 4 Page 9
Example for a device to be protected by fuses at 10 kA or less. SPECIFIC FUSE MANUFACTURER AND TYPE LISTING
WHEN PROTECTED BY A FUSE OF THE SPECIFIC MANUFACTURER, TYPE, AND AMPERE RATING AS MARKED BELOW, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN CIRCUITS CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT AT THE MAXIMUM VOLTAGE MARKED.
SHORT-CIRCUIT CURRENT
VOLTAGE
RATING
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
MANUFACTURER
TYPE
(AMPERES)
10
480
MFG. A
F1
1500
10
480
MFG. B
F2
1500
Example for device to be protected by fuses above 10kA. SHORT-CIRCUIT WITHSTAND/CLOSING RATING WHEN PROTECTED BY FUSES
WHEN PROTECTED BY A FUSE OF THE SPECIFIC FUSE CLASS AND MAXIMUM AMPERE RATING AS MARKED BELOW, THIS TRANSFER SWITCH IS SUITABLE FOR USE IN A CIRCUIT CAPABLE OF DELIVERING THE SHORT-CIRCUIT CURRENT AT THE MAXIMUM VOLTAGE MARKED.
SHORT-CIRCUIT CURRENT
VOLTAGE
FUSE CLASS
RATING
(RMS SYMMETRICAL AMPERES X 1000)
(VOLTS AC, MAXIMUM)
65
480
J
1600
65
480
L
2000
(AMPERES)
§
© 2015 National Electrical Manufacturers Association
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