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Half-Trip Ground Fault Testing

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    Half-Trip Ground Fault Testing

    Question on ground fault testing of the residual type. The only way I can make sense of testing the neutral and phase current transformers together and to get the GFP to trip would be to conduct a "half-trip" test. Is that the correct interpretation of this section? The field testing procedures I have read from Eaton and Square D only require to do a "No-trip" test with the Phase and Neutral current transformer. Is it standard practice for your company to perform "half-trip" testing? Any input would be appreciated. Thanks.



    NETA ATS-2021
    7.14.B.5
    "For summation type systems utilizing phase and neutral current transformers, verify correct polarities by applying current to each phase-neutral current transformer pair. This test also applies to molded-case breakers utilizing an external neutral current transformer."

    7.14.D.5
    "The ground fault protective device shall operate when current direction is the same relative to polarity marks in the two current transformers. The ground fault protective device shall not operate when current direction is opposite relative to polarity marks in the two current transformers."

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    Quote Originally Posted by RedBrick View Post
    Question on ground fault testing of the residual type. The only way I can make sense of testing the neutral and phase current transformers together and to get the GFP to trip would be to conduct a "half-trip" test. Is that the correct interpretation of this section? The field testing procedures I have read from Eaton and Square D only require to do a "No-trip" test with the Phase and Neutral current transformer. Is it standard practice for your company to perform "half-trip" testing? Any input would be appreciated. Thanks.



    NETA ATS-2021
    7.14.B.5
    "For summation type systems utilizing phase and neutral current transformers, verify correct polarities by applying current to each phase-neutral current transformer pair. This test also applies to molded-case breakers utilizing an external neutral current transformer."

    7.14.D.5
    "The ground fault protective device shall operate when current direction is the same relative to polarity marks in the two current transformers. The ground fault protective device shall not operate when current direction is opposite relative to polarity marks in the two current transformers."
    It has always been my practice to perform no-trip test between neutral CT and all Phase CTs, followed by half-trip between the neutral CT and each phase CT.

    In practice, if you performed a no-trip test on all phases then it would technically prove the circuit will energize. That is not to say it will trip at the correct value. Performing only half-trip test would just verify that it trips, and not that both CTs are correct in polarity and size.

    Thus performing both test verifies that all components operate correctly. I have found the CT inside the breaker wired incorrectly, thus I test all phases.

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    Half-trip is a slick way to test ground fault when your set cant put out enough current.

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    Appreciate the responses so far.

    I understand what half-trip testing is and that it is helpful for testing when your test set isn't large enough to test at full current.

    My real question is about what NETA requires. Based on the quoted section from the 2021 ATS do you think half-trip testing is being required or is the quoted section referring to something else?

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    Quote Originally Posted by RedBrick View Post
    Appreciate the responses so far.

    I understand what half-trip testing is and that it is helpful for testing when your test set isn't large enough to test at full current.

    My real question is about what NETA requires. Based on the quoted section from the 2021 ATS do you think half-trip testing is being required or is the quoted section referring to something else?
    It's definitely confusing language. Because of the use of the word "polarity", I believe this section requires (1) either a half trip or trip test AND (2) a no trip test.

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    Quote Originally Posted by anonymous View Post
    It's definitely confusing language. Because of the use of the word "polarity", I believe this section requires (1) either a half trip or trip test AND (2) a no trip test.
    Agree with this. You just need to prove that it trips as intended and does not trip when polarity is correct. No trip test basically proves the system wiring and the trip test ensures that the pickup levels and timing is right. The half trip is a good trick to use when you don't have the current you need but I always opt for the full trip whenever possible.

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    Thanks again for all of the responses. Just wanted to get some input from others on this topic, appreciate the input.

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  15. alf583 is offline Junior Member Pro Subscriber
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    Quote Originally Posted by SecondGen View Post
    Agree with this. You just need to prove that it trips as intended and does not trip when polarity is correct. No trip test basically proves the system wiring and the trip test ensures that the pickup levels and timing is right. The half trip is a good trick to use when you don't have the current you need but I always opt for the full trip whenever possible.
    Thank you for this "explain it like I'm 5" of the purpose of the tests.
    I'm a new guy at my company and I'm getting sent to do my first solo GF next week.
    I have some technical docs explaining testing procedures, but I still get a little lost in the sauce.

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