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#28806 - 08/31/03 02:33 PM phase question  
Eandrew  Offline
Joined: May 2002
Posts: 68
seattle, wa, usa
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

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#28807 - 08/31/03 02:46 PM Re: phase question  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
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.

#28808 - 08/31/03 02:54 PM Re: phase question  
Eandrew  Offline
Joined: May 2002
Posts: 68
seattle, wa, usa
thanks paul. this forum is always a good place to turn to when your not sure. Thanks again.

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