Phase to ground/N 277v. Phase to Phase 0v

[eric38]

Existing installation. Has been working for a long time before this morning.
3 phase system, but only using two legs to feed a fused disconnect.
From fused disconnect, goes to a 480 to 240 xfrmr, then feeds a telecom site
At the line side disconnect and xfrmr, have 277 to G/N, 0v phase to phase

Other than the two hot legs we are measuring being the same phase, is there any other way phase to phase would be zero?
Physical damage of some sort?

 

[don_resqcapt19]

You have an open in one of the phases somewhere. Could be anywhere from the utility to the load.

 

[petersonra]

You have an open in one of the phases somewhere. Could be anywhere from the utility to the load.

how could you have 277 to neutral from both phases if one phase was open?

 

[texie]

how could you have 277 to neutral from both phases if one phase was open?

Across the load of the transformer winding.

 

[petersonra]

Across the load of the transformer winding.

I get you. You are reading the same phase which is why the phase to phase voltage is zero.