How can there be a non-zero voltage difference between Phase A on the left and Phase A on the right when they come from the same power source?

Question

Hi StackExchange community,

Here I have a wiring diagram that represents a portion of a circuit found in a hospital.

The voltage difference was measured between phase A on the left and the phase A on the right and the voltage difference was found to be 120 V. The voltage difference between phase A on the left and phase A on the right should be 0 V.

Can anyone suggest possible reasons for this malfunction? A theory of mine was that the connections between phases may have been flipped somewhere along the way but I would appreciate some input.

Thank you.

Answer 1

I don't see any "phase A" I see lots or a's b's and c's.

However, I am guessing you mean at the panels.

Since in your diagram, they appear to be isolated what you are reading may be a meter effect.

However it is far more likely there is a common neutral / ground connected in there somewhere you are not showing us, in which case the transformers may not be connected the same way.