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Thread: Can a short trip a GFI without blowing a fuse?

  1. #1
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    Default Can a short trip a GFI without blowing a fuse?

    Simple question: can a short on a strand of lights trip a GFI outlet or breaker without popping a fuse on the controller?

    The background: for Halloween I tested out a new pre-assembled AlphaPix16 box (with 350W PSU) and controller from Holiday Coro, which only powered a few lights inside a pumpkin. I put a short 3 pixel ribbon in the pumpkin, but a number of times I'd find something had tripped the GFI outlet and I'd have to press the reset button on the outlet. The AlphaPix16 has 5 amp fuses on each output, so if there were a short, wouldn't it pop the fuse rather than tripping the GFI? Put differently, could something below 5 amps trip the outlet? I hot glued the end of the ribbon, but it looks like the glue filled the end of silicon jacket well enough to make a seal. The only other gear was a raspberry pi and a router, which I haven't had problems with before. I put the AlphaPix16 on a separate circuit in my garage to isolate it, which confirmed it is the AlphaPix16 box tripping the GFI.

    I'll keep running a basic sequence in the garage for a couple days to see if it trips again with different set of lights. Perhaps my pumpkin pixel strip is just bad, but I'd like to establish there is nothing wrong with the controller before the Christmas season arrives.

    Advice or words of wisdom?

    Thanks

  2. #2
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    Default Re: Can a short trip a GFI without blowing a fuse?

    A fuse or circuit breaker protects against an over current situation (too many amps). GFCI protects against something different. Sorry answer is that it measures the current going out the hot wire and compares it to the current coming back in on the neutral. If there is a discrepancy, it means that current is going since it shouldn't (the ground, a person, etc.), so it shuts off the power (very quickly too).

    So to answer your question, yes, a GFCI can shut off with less than 5 amps. In fact, it only takes a discrepancy of a few milliamps to trip a GFCI.

  3. #3
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    Default Re: Can a short trip a GFI without blowing a fuse?

    There is more to it than GFCI could trip it. GF should not trip on a “short circuit.” The GFCI circuit trips GF only when current leaks to ground, However the GFCI device also has thermal and magnetic tripping elements, and either could trip before a fuse blows. The question was: could a SHORT CIRCUIT trip without popping a fuse. A short circuit is generally instant, therefore the magnetic feature of the tripping circuit will trip the GFCI device. Now, a quantity GFCI device will trip the circuit fast enough the fuse will not blow. So yes.......but now, was it a short circuit or a ground fault?
    Last edited by mrGrumpy; 11-01-2018 at 10:07 PM.
    In Lights Therapy

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  5. #4
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    Default Re: Can a short trip a GFI without blowing a fuse?

    Quote Originally Posted by jackal24 View Post
    A fuse or circuit breaker protects against an over current situation (too many amps). GFCI protects against something different. Sorry answer is that it measures the current going out the hot wire and compares it to the current coming back in on the neutral. If there is a discrepancy, it means that current is going since it shouldn't (the ground, a person, etc.), so it shuts off the power (very quickly too).

    So to answer your question, yes, a GFCI can shut off with less than 5 amps. In fact, it only takes a discrepancy of a few milliamps to trip a GFCI.
    Thanks for the quick answer. It is a GFCI outlet, so you may have nailed it. I’ll test it for a couple days with different lights to see if I can isolate the pumpkin strand of lights versus the controller/ PSU.

  6. #5
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    Default Re: Can a short trip a GFI without blowing a fuse?

    Quote Originally Posted by jalder View Post
    Thanks for the quick answer. It is a GFCI outlet, so you may have nailed it. I’ll test it for a couple days with different lights to see if I can isolate the pumpkin strand of lights versus the controller/ PSU.
    It could also potentially be the GFCI outlet as well that is the problem

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