TCC plot reference voltage

[brainsalad]

Hello,

Suppose I have a 3-phase 480V panel which has 277V branch positions. Is it correct that the TCC plot reference voltage should
be 480V? I am trying to plot a branch circuit breaker and am unsure if it should be 277V or 480V. Will a single pole single phase breaker off of such a panel see the 480V fault current?

Thanks.

 

[rcw retired EE]

Use 480V. It is a 480V/277V system. Fault current is the same. The breaker overcurrent trip unit cannot tell if it is a 480V phase-phase fault or a 277V phase-ground fault. It is the same trip curve whether it is a 30A three-pole or a 30 Amp single pole breaker.

The curve drawing software might incorrectly move the curve by a 1.732 factor if you enter 277V for the base. Try it and see.