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Thread: Circuit short help

  1. #1
    DIY Senior Member rockycmt's Avatar
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    Default Circuit short help

    See the wiring diagram below. It is a small circuit. Homerun to the first outlet. It shorts out at the breaker when the switch is thrown to on. There is no load on the circuit so it is not an amp issue. Where is the problem?
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  2. #2
    Plumber Cass's Avatar
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    Somewhere in the circuit...a diagram does not show problems...

  3. #3

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    *Very* rarely, an outlet may have a manufacturing defect where the hot and neutral is shorted. (As in I have only seen this happen once.)

    Then other than that, turn off the main breaker, disconnect ALL the wires going to the circuit and use an ohm meter or continuity tester to test the wires.

    Remove the light bulb first, then there should be NO continuity from any wire to any other wire.

    Hot to neutral.
    Hot to ground.
    Neutral to ground.

    When you see from the breaker panel that there is a short between two wires, you can then disconnect the wires further down the line and test from there.

    Sometimes a metal clamp may cut into a wire causing a short. Or there my be a bare wire pointing out and touching a grounded electrical box. Or there may be a staple *through* the wire shorting it. Or when pulling wires with a lot of force through a hole in metal, this can strip the wire and cause a short to ground. Etc.

    How to use a continuity tester...
    http://www.dinosaurelectronics.com/Test_Fuse.htm

  4. #4
    DIY Senior Member rockycmt's Avatar
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    All very good points Billy Bob. I will test the line between the switch and the fixture. I must have a staple stuck in it or a rip. I will confirm. In a major job does every wire get tested during 'roughIn' to catch things like this? I can see this heppening after walls are put up.

  5. #5
    Homeowner Thatguy's Avatar
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    Put a light bulb or a radio that's turned on across the CB while the CB is off.
    When the bulb goes out or the radio stops playing you've cleared the short.
    If the bulb never goes on or the radio doesn't play it is a bad CB.

  6. #6
    DIY Senior Member Rich B's Avatar
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    Are the boxes metal? You can sometimes use your nose to tell you where a dead short is after the breaker trips. Romex inside a metal box could have a nicked spot on a wire touching the box. OR BX without the proper "redhat" anti short bushing can have a bare spot at the wire where it exits the metal jacket. I worked with a guy who would say..."smell the plugs" to look for a shorted circuit....

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