weird voltage readings

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new guy
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weird voltage readings

Post by new guy » Mon Feb 05, 2007 5:20 pm

I came across weird volt readings in work today. Maybe someone has an explanation. Working with THREE PHASE 480V heaters. At the disconnect the voltage (when the disconnect was open) was 480V between any two legs. And 277V from any leg (3) to ground. But with the disconnect closed, voltage between one leg and ground was 0V and between one other leg and ground was @ 500V. Possibly what I thought was ground was not really ground? And there was no good ground?

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Post by haklesup » Fri Feb 09, 2007 1:55 pm

The question is hard to answer because we don't know if the source is Delta or Wye connected. Same for the load. There also may be some confusion between Ground and Neutral Return conductors.

I suspect the load wires the Ground to one of the phases and uses that like a neutral. but I can only guess. If the heaters have different power settings, you may even see your readings change when you change the setting.

Best advice is to measure the resistance (continuity) between all leads on the load while it is disconnected (in other words, "Ohm it Out"). In the end, I don't quite understand why you would have more than 480V in any configuration.

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Post by High4Volts » Fri Feb 09, 2007 4:38 pm

Did you use an amp clamp to get the amp draw by chance?

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Chris Smith
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Post by Chris Smith » Fri Feb 09, 2007 5:11 pm

Always "load test" you voltages to ensure no spurious voltage readings are found.

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