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What is ground fault blocking capability?

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    What is ground fault blocking capability?

    A ground fault system inspection on a 480Y/277V switchgear would not require which of the following?
    Correct Answer: None of the above
    Your Answer: Blocking capability

    - What is "Blocking capability?" never heard that term in association with GF.
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    Your question interested me, so I hit up the Google box for answers.
    It would seem that blocking capability has to do with Zone Selective Interlocking, which I have never dealt with, so it is up to you to research this subject for your own edification.
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    Any ground fault relay with zone interlocking will respond instantaneously regardless of time delay setting unless a restraint signal (which is indicative of a ground fault further downstream in the next protective zone) acts to change the mode of operation to the pre-set time delay.

    You see this a lot when testing solid state trip units because you have to create that blocking signal with a jumper if the circuit breaker is not in the cell in order to test the short circuit and ground fault time delays, but this feature may also exist in other types of ground fault protection systems.
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    Last edited by SecondGen; June 23, 2015 at 11:20 AM.

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