ECN Forum Forums General Topics of the Trade General Discussion Area phase question

I wanted to clarify my understanding of single phase on a three phase system:

single phase:

120v = one pole breaker
240v = two pole breaker

three phase:

120v or 277v single phase = one pole breaker
208v or 480v single phase = 2 pole breaker
208v or 480v three phase = 3 pole breaker


208v or 480v

You can have a single-phase circuit tapped from a three-phase supply either by connected phase-to-phase, or phase-to-neutral.

The breaker needs to open all ungrounded conductors, so with a 3-ph wye system a phase-to-phase load needs a 2-pole C/B, while a phase-to-neutral load needs only a single-pole, as you've stated.

The only cases that might want adding to your list would be something like a corner-grounded 240V delta, where one of the phases is actually grounded.

thanks paul. this forum is always a good place to turn to when your not sure. Thanks again.