what causes a 3 phase 480 circuit to read 277 VAC from each leg to ground but not read 480 VAC from leg to leg

[skihard]

What causes a 3 phase 480 circuit to read 277 VAC from each leg to ground but not read 480 VAC from leg to leg

 

[don_resqcapt19]

An open phase with a 3 phase load backfeeding the open phase.

 

[infinity]

What are the voltage readings from the three phases: A-B, A-C, B-C?

 

[skihard]

all zero.

What are the voltage readings from the three phases: A-B, A-C, B-C?

 

[synchro]

What are the voltage readings from the three phases: A-B, A-C, B-C?

all zero.

Could be two open phases, and L-L loads (single phase or delta) are making the voltages at the open phases be the same as that of the live phase (i.e., cause zero volts between phases).

 

[retirede]

Two of three fuses blown!

 

[skihard]

Thank you all.

 

[LarryFine]

I'd need to know where you're taking these measurements to comment.

 

[Jraef]

My guess... you are using a DMM, not an induction tester (aka Wiggy or Knopp tester).