low voltage (unintended) on 3 phase 120v circuit

1288 Views 7 Replies 7 Participants Last post by bobelectric, May 11, 2014

itsgroundedman

Discussion Starter · May 10, 2014

I have a 3phase 4 wire 120/208 panel fed from a transformer that is fed from a 277/408 panel. We turned it on and while testing voltage at a receptacle, it read 60v. I won't be back to trouble shoot til Tuesday but I can't stop thinking about it. Two explanations that I could think of is a loose neutral, or insufficient bonding of the neutral to ground from the xfmr. What are your opinions on these theories?

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nickjv

· #2 · May 10, 2014

Agree

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chewy

· #3 · May 10, 2014

One of your phases has completely dropped out perhaps?

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bkmichael65

· #4 · May 10, 2014

Line to neutral or line to ground?

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itsgroundedman

Discussion Starter · #5 · May 10, 2014

Haven't done any measurements myself but I was told line to neutral

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don_resqcapt19

· #6 · May 10, 2014

itsgroundedman said:
Haven't done any measurements myself but I was told line to neutral

If that is a line to neutral voltage then the transformer bonding and grounding has nothing to do with the issue.

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Big John

· #7 · May 10, 2014

Need to do L-N, N-G, L-G and use a low impedance tester.

I'm thinking either open neutral or you actually have a dead circuit and you're just seeing ghost voltage.

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bobelectric

· #8 · May 11, 2014

Sounds like the 480 in lost a phase.

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