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Bus bar short circuit duration

Bus bar short circuit duration

Bus bar short circuit duration

(OP)
If the Incoming breaker can clear the fault within 3 cycles (50 ms), can the bus bar be rated for 3 cycles? Is there any standard (NEC/ANSI) that requires the bus bar to be rated at 1s or 3s.

RE: Bus bar short circuit duration

What voltage level?

RE: Bus bar short circuit duration

(OP)
It is of low voltage.

RE: Bus bar short circuit duration

Do you really have breakers and relaying that can operate in 3 cycles?

RE: Bus bar short circuit duration

Equipment bus bracing fault duration is generally based on relevant NEMA or ANSI standard. With a 3 cycle rating (standard for MCCs for example), clearing within 3 cycles is possible but will limit ability to coordinate with downstream molded case breakers or fuses. Longer durations can be specified - if manufacturer is willing to provide.

NEC doesn't have any requirements for this. It only requires that all equipment be operated "within its rating".

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