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Testing for voltage drop

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    Testing for voltage drop

    Can someone tell me where the fault is, I think I know but I don’t like shoveling dirt!
    Had a service call today, a boat lift on a pier was not working, (this lift has been working for years prior with no issues), the lift is 120 volt 30 amp breaker, when I tried the up switch the contractor just hummed, checked the voltage at the lift under load it dropped to 93 volts. Went to the beginning of the pier at the sub panel, the breaker voltage was 93 volts under load. Checked the pier panel main, the voltage again dropped to 93 volts. Went to the house service pier panel breaker, there was no voltage drop at the breaker under load. The size of the wire is fine. Can I assume there’s a fault in the wire from the house panel to the pier panel because of the voltage readings? (FYI , I ran my own temporary power to the lift and the lift worked fine).

    #2
    Yep, faulted line
    you can get a pretty good fault finder cheap. It will put you right on it, within an inch or two. Got a friend at the POCO?


    just for kicks, I looked up a Dynatel 573A. Saw one in AZ that sold for &100 and included the horseshoe!
    mine cost me 250 3 years ago. Paid for it the very first job. Water well line about 500’ long in a pasture fed from a barn. Set it up, walked right to it.. had it repaired in 30 minutes.
    Last edited by Hv&Lv; 09-06-19, 08:20 PM. Reason: Looked up a used Dynatel online

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      #3
      Wow...I think I paid $400 for the one I have over 30 years ago. Even that paid for itself many times over.

      Tom
      TBLO

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        #4
        190906-2120 EDT

        Looks to be an interesting instrument.

        See manual at https://multimedia.3m.com/mws/media/...ues-manual.pdf

        For post #1 I would suggest looking for a poor connection. Check for any point where there might be a splice or inadequate connection. The resistance for the problem is high relative to the expected resistance of the cable, but it is still low compared to an open circuit. The fault resistance might be in the range of 27/30 = 0.9 ohms. Possibly somewhat higher because load current may not be 30 A.

        You can perform tests that will identify a hot or grounded conductor problem, if the fault is in only one of those wires.

        .

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          #5
          My Ideal branded locator doesn’t have near the # of pages in the instruction manual. It’s analog as well.

          Isolate your conductors on both ends. Stick one lead of your T+Pro in the ground and the other to a bared conductor. If it squeaks, it’s faulted. A megger is better or a good VOM with a high resistance scale will usually work.

          You already know its faulted, the fun part is getting a new tool. Make it two, get a Megger as well.
          Tom
          TBLO

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