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Bad 480V Circuit Breaker ??

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  • Bad 480V Circuit Breaker ??

    I was trouble-shooting a pole mounted parking lot lite, the panel was a 277-480V remote contolled Square-D, the lites are 480V so the breakers are 2 pole when using a volt meter you should get 277 to ground on both legs and get 480V phase to phase , on a bad breaker you will still get 277V to ground but phase to phase you will get 0 volts , I find that hard to grasp. Here is a good one the 2 pole breaker below the one I was working on read 577V to ground on one phase and 277V on the other,phase to phase was aprox 920V, explain this if you can ?? I just replaced my battery in my volt meter.. the meter was fine, we also used another volt meter with the same results?? see if you can answer this please

  • #2
    Re: Bad 480V Circuit Breaker ??

    I don't know how to explain it, but I do know I would hate to look at my meter and see 900+ volts show up.

    What action have you taken?
    Did you measure the incoming power?

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    • #3
      Re: Bad 480V Circuit Breaker ??

      jsut a guess but the transformer shorting internal on the higher voltage phase,
      or some other higher voltage line energizing the line to the transformer,

      or some type of miss wiring on the primary side.

      re reading the post I think you my have a miss wired phase, and two that are correct, and some how the third phase is series up with one of the other phases, creating the high leg, would guess the "neutral" of the Wye on the one lines/transformer was removed in some way to series to one of the other phases, I do not know but that is my guess, I am not very good with math on three phase but the 577 volts seems about the right voltage on a zig zag winding like that,
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      Last edited by BHD; 08-12-2008, 07:35 PM.
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      • #4
        Re: Bad 480V Circuit Breaker ??

        Rather than banging your head on the wall, try to take measurements close to the point of service entrance to the building. Also sometimes RF energy makes digital meters read wrong. Please try this using a Simpson 260 or 270 setup on the 0-1000 AC Volts range and report your measurements.

        If there are transformer connection problems or a bad winding contact the electric power company unless the transformers are inside and owned by the company that owns or leases the building.

        Forget about the bad breaker. Measure Voltage at the input. Then go to where the main service entrance for the building is and measure it there.

        Question: Exactly where were you measuring the Voltages?
        Last edited by Woussko; 08-14-2008, 01:34 AM.

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        • #5
          Re: Bad 480V Circuit Breaker ??

          Did you try reading voltage at the lugs feeding the panel? Getting messed up voltages on a breaker like that, I would have immedietly tried to determine whether the voltages come into the panel that way or if it is the breakers in the panel. If the voltages come into the panel that way, then you can work backwards and find the source of troubles, whether it be in the building or a utlity problem. If the voltages come in to the panel fine, then you have reduced it to one panel and can start troubleshooting at that point. Right now, you have no reference point to work from and it could be nearly anything.

          Jeff

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          • #6
            Re: Bad 480V Circuit Breaker ??

            480 is not for amateurs, death comes in a instant, call a licensed electrician.

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            • #7
              Re: Bad 480V Circuit Breaker ??

              I wonder it he messed up and is took Voltage readings of the output from a ballast rather than at the breaker. Being he never did reply my bet is it's all just *(&^%$ to see if anyone would respond.

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              • #8
                Re: Bad 480V Circuit Breaker ??

                Its not uncommon to develop 100s of volts of capacitance on long runs. However this situation certainly requires the aid of a trained professional.

                I am a NY state certified electrician, I can assist you to correcting this problem. Toll free (877) 292-4568 Ext 704

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