Bus bar short circuit duration

[NickParker]

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.

 

[wroggent]

What voltage level?

 

[NickParker]

It is of low voltage.

 

[HamburgerHelper]

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

 

[dpc]

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".

 

[Marmite]

There's a useful technical publication on busbar design here, and also an accompanying webinar.
Regards
Marmite

http://copperalliance.org.uk/resource-library/electrical-resources