stevebea
Senior Member
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- Southeastern PA
Its my understanding that SCCR pertains to assembly ratings and interrupting ratings pertain to overcurrent protective devices. Is this correct?
SCCR vs. Interrupting Rating
- Thread starter stevebea
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- Wisconsin
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- PE (Retired) - Power Systems
Yes. . ...............
stevebea
Senior Member
- Location
- Southeastern PA
Thanks Jim!
weressl
Esteemed Member
To be more accurate and descriptive there is withstand rating, which describes the maximum A or MVA rating that an assembly can withstand without damage of its function and the interrupting rating which describes what A or MVA can a device clear. The later one could be an one-time rating like MCBS that are rated to clear the maximum fault ONCE. The remaining interrupting capacity is not tested or rated, so the device is expected to be replaced after that.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Actually withstand is an 'old school', althought still very common, term used particularly with switchgear. SCCR is a more general term which would encompass terms like withstand and bus bracing.
weressl
Esteemed Member
IEEE C37.20.1 ME LV Switchgear
5.1 General
The ratings of a switchgear assembly are designations of operating limits under specified conditions of ambient temperature, temperature rise, etc. Where the switchgear assembly comprises a combination of primary and secondary circuits, each may be given ratings.
Low-voltage switchgear shall have the following ratings:
a) Rated maximum voltage
b) Rated power frequency
c) Rated insulation level
d) Rated continuous current
e) Rated short-time withstand current
f) Rated short-circuit withstand current
The ratings of a switchgear assembly are designations of operating limits under specified conditions of ambient temperature, temperature rise, etc. Where the switchgear assembly comprises a combination of primary and secondary circuits, each may be given ratings.
Low-voltage switchgear shall have the following ratings:
a) Rated maximum voltage
b) Rated power frequency
c) Rated insulation level
d) Rated continuous current
e) Rated short-time withstand current
f) Rated short-circuit withstand current
The designated ratings in this standard are preferred, but are not to be considered restrictive. In addition to these ratings, a switchgear assembly may have interrupting or switching capabilities, which are determined by the ratings of the particular interrupting and switching devices that are integral parts of the switchgear assembly. Refer to specific standards for the ratings of these devices.
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5.4.3 Rated short-time withstand current
The rated short-time withstand current of a LV ac switchgear assembly, or a LV dc switchgear assembly rated 300V or 325V (dc), is the designated limit of available (prospective) current at which it shall be required to withstand its short-time current duty cycle (two periods of 0.5 s current flow, separated by a 15 s interval of zero current) at rated maximum voltage under the prescribed test conditions. This current is expressed in rms symmetrical amperes and is measured from the envelope of the available current wave at a time one-half cycle after current is established.
The rated short-time withstand current of a LV dc switchgear assembly for use with solid-state rectifiers (regardless of rated voltage), or rated above 325V (dc), is the designated limit of available (prospective)sustained rms current it shall be capable of carrying for not less than 250 ms. Both LV ac and LV dc switchgear assemblies shall have a preferred short-time withstand current rating equal to the short-time current rating of the smallest frame size circuit breaker used in the assembly, as listed in ANSI C37.16-2000.
The rated short-time withstand current of a LV ac switchgear assembly, or a LV dc switchgear assembly rated 300V or 325V (dc), is the designated limit of available (prospective) current at which it shall be required to withstand its short-time current duty cycle (two periods of 0.5 s current flow, separated by a 15 s interval of zero current) at rated maximum voltage under the prescribed test conditions. This current is expressed in rms symmetrical amperes and is measured from the envelope of the available current wave at a time one-half cycle after current is established.
The rated short-time withstand current of a LV dc switchgear assembly for use with solid-state rectifiers (regardless of rated voltage), or rated above 325V (dc), is the designated limit of available (prospective)sustained rms current it shall be capable of carrying for not less than 250 ms. Both LV ac and LV dc switchgear assemblies shall have a preferred short-time withstand current rating equal to the short-time current rating of the smallest frame size circuit breaker used in the assembly, as listed in ANSI C37.16-2000.
5.4.4 Rated short-circuit withstand current
The rated short-circuit withstand current of a LV ac assembly, or a LV dc switchgear assembly rated 300 or 325V (dc), is the designated limit of available (prospective) current at rated maximum voltage that it shall be required to withstand for a period of no less than four cycles on a 60Hz basis under the prescribed test conditions. This current is expressed in rms symmetrical amperes and is measured from the envelope of the available current wave at a time 1/2 cycle after current is established.
The rated short-circuit withstand current of a LV ac assembly, or a LV dc switchgear assembly rated 300 or 325V (dc), is the designated limit of available (prospective) current at rated maximum voltage that it shall be required to withstand for a period of no less than four cycles on a 60Hz basis under the prescribed test conditions. This current is expressed in rms symmetrical amperes and is measured from the envelope of the available current wave at a time 1/2 cycle after current is established.
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