Unbalanced 3-phase

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TheChevre

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Marlborough, MA USA
Forgive me if this is simple, but my journeyman was stumped to:

120/208 panel, phase A to ground=120, phase B to ground=120, phase C to ground=150?

And here’s the kicker: we installed 2 2-pole breakers, one on top of the other, and both circuits had the 150v leg. I can’t imagine they’re both hitting phase C. What the heck?

First post, long time lurker. I did the due diligence to search if this has been answered before as standard forum etiquette suggests. Thanks for any answers
 
TheChevre said:
Forgive me if this is simple, but my journeyman was stumped to:

120/208 panel, phase A to ground=120, phase B to ground=120, phase C to ground=150?

And here’s the kicker: we installed 2 2-pole breakers, one on top of the other, and both circuits had the 150v leg. I can’t imagine they’re both hitting phase C. What the heck?

First post, long time lurker. I did the due diligence to search if this has been answered before as standard forum etiquette suggests. Thanks for any answers
Click to expand...

What were the voltages from A to B, B to C, and C to A?

Depending on where you started on the bus with your stacked breakers, you could wind up with two C phases.
 
oldsparky52 said:
What were the voltages from A to B, B to C, and C to A?

Depending on where you started on the bus with your stacked breakers, you could wind up with two C phases.
Click to expand...

Especially if you were using half-sized breakers. Those go two slots for the same phase, then two slots for the next phase, etc. in the case of a 120/240 panel (single phase) the full size breakers occupy two full size slots, and 240 requires offset placement. A quad breaker for the same panel will label the two outside as one 240V circuit and the two inside as the other.
 
Seems to me that if you have 150V on C you should have more than 208V on any two legs that involves C.
1.) Are you sure it's a 208V "Y"?
2.) Have you checked with a 2nd/different meter?
 
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