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Thread: Insulation Testing "Megging" Residential Wiring

  1. #1
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    Cool Insulation Testing "Megging" Residential Wiring

    Can a "megger" or insulation tester be used to test for insulation integrity, ground faults, and short circuits, for residential wiring?

    Branch circuits and feeder conductors are exposed where they terminate. How can an insulation tester, "megger", test for insulation integrity if the insulation is removed from the conductors where they terminate?

    If insulation testers can be properly used for residential wiring, it seems to me a great way to check the integrity of the branch circuits before sheet rocking. It can also be used for troubleshooting.

    Thank you!

  2. #2
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    How can an insulation tester, "megger", test for insulation integrity if the insulation is removed from the conductors where they terminate?

    You are not testing the insulation, you are testing conductivity between the conductor and another conductive object. The termination will also be insulated from other items. Poor insulation will allow conductivity and this is what the megger is really showing you. Poor insulation that is otherwise isolated from other conductive objects will not give a bad test.

  3. #3
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    I have seen posts here where some seem to think that nicked insulation can be detected with a megger. Low voltage like 120V won't jump a gap of more than about .005".
    Bill

  4. #4
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    Kwired,
    I understand you are explaining that a megger will test for conductivity between two conductors, like a ground fault or a short circuit. Is that correct?
    I also understand you are explaining the exposed conductors at the termination points do not make a difference for a megger test? is that correct? It seems to me that it would be a good idea to disconnect the conductors from the termination points before performing a megger test for branch circuits, otherwise the megger test will be testing the device the conductors are connect to. Right?
    Have you ever performed a megger test for residential branch circuits?
    Thank you,
    Paul Wilson

  5. #5
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    There are quite a few threads on here having to do with megging. Do a search. Electronic devices such as dimmers, gfci, afci, tvss, should not be megged. Good practice and NEC 2005 "110.7 Insulation Integrity.
    Completed wiring installations shall be free from short circuits and from grounds other than as required or permitted in Article 250."
    would seen to support the use of a megger although not specifically stated.
    Tom
    TBLO

  6. #6
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    Quote Originally Posted by paulgarett View Post
    Kwired,
    I understand you are explaining that a megger will test for conductivity between two conductors, like a ground fault or a short circuit. Is that correct?
    I also understand you are explaining the exposed conductors at the termination points do not make a difference for a megger test? is that correct? It seems to me that it would be a good idea to disconnect the conductors from the termination points before performing a megger test for branch circuits, otherwise the megger test will be testing the device the conductors are connect to. Right?
    Have you ever performed a megger test for residential branch circuits?
    Thank you,
    Paul Wilson
    Depends what you are testing for and if the device can take the test voltage.

    If you intend to test circuit conductors only isolate them so you are not testing whatever they may be connected to.

    The megohmmeter I use is a very inexpensive one but I usually use it for troubleshooting and finding simple pass/fail items. It finds lots of things that a typical digital meter will leave you guessing at because of the higher test voltage. I have never used it to check a circuit and determine that it getting near the time to take action, don't know if it is accurate enough device for this in the first place.

  7. #7
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    Quote Originally Posted by paulgarett View Post
    Kwired,
    I understand you are explaining that a megger will test for conductivity between two conductors, like a ground fault or a short circuit. Is that correct?
    I also understand you are explaining the exposed conductors at the termination points do not make a difference for a megger test? is that correct? It seems to me that it would be a good idea to disconnect the conductors from the termination points before performing a megger test for branch circuits, otherwise the megger test will be testing the device the conductors are connect to. Right?Have you ever performed a megger test for residential branch circuits?
    Thank you,
    Paul Wilson
    I disconnect the sensitive electronics, GFCI's, unplug everything in the home, etc. Then test. If the test is low, then start breaking the circuit up by disconnecting receps, etc.

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