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Thread: GFI tripping

  1. #1
    DIY Junior Member ferd's Avatar
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    Question GFI tripping

    Installed a gfi duplex in place of standard duplex. Vent fan uses the same feed. gfi trips when you tune the fan off. Wired the fan direct to the feed, not thru the gfi, but gfi still trips. Any suggestions welcome. Thanks

  2. #2
    Electrical Contractor/Instructor jwelectric's Avatar
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    It is wired incorrectly or something in the box is touching something

  3. #3
    DIY Junior Member ferd's Avatar
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    Already checked. gfi isn't even in the box to touch anything.

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    Plumber jimbo's Avatar
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    Look for an issue with your neutrals. If a neutral connection at the load has a path to return thru the GFI, but also another neutral wire connected, then the current can split and the gfi sees a fault. Or if the current from a different load is returned to the gfi neutral...same thing,

  5. #5
    DIYer, not in the trades LLigetfa's Avatar
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    Some of the sparkies on this forum scoff at me when I say that induction loads can induce a voltage when turned off but that is exactly what is happening. The magnetic field in the motor collapses just like an ignition coil does when the points open. Some motors can act as generators as the rotation inertia diminishes when the power is removed. This can trip a GFCI.

    The fact that it is tripping a GFCI when the fan is not protected by the GFCI however sounds very suspiciously like a poor neutral bond or a very long run of light gauge wire.

    The common cure for motor loads tripping a GFCI is to use a double pole switch designed to switch 240 volt loads.

    http://homerepair.about.com/od/elect...ch_types_3.htm

  6. #6
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by LLigetfa View Post
    Some of the sparkies on this forum scoff at me when I say that induction loads can induce a voltage when turned off but that is exactly what is happening. The magnetic field in the motor collapses just like an ignition coil does when the points open. Some motors can act as generators as the rotation inertia diminishes when the power is removed.
    This is very true and I agree with your comments

    Quote Originally Posted by LLigetfa View Post
    This can trip a GFCI.
    This is very untrue and I completely disagree.
    What makes a GFCI open is an imbalance between the hot and neutral and this alone.

    Quote Originally Posted by LLigetfa View Post
    The fact that it is tripping a GFCI when the fan is not protected by the GFCI however sounds very suspiciously like a poor neutral bond or a very long run of light gauge wire.
    This again would have no effect on a GFCI. A loose neutral would only open the circuit

    Quote Originally Posted by LLigetfa View Post
    The common cure for motor loads tripping a GFCI is to use a double pole switch designed to switch 240 volt loads.
    a waste of time and money

  7. #7
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by jwelectric View Post
    This is very true and I agree with your comments
    ...
    This is very untrue and I completely disagree.
    What makes a GFCI open is an imbalance between the hot and neutral and this alone.
    ...
    This again would have no effect on a GFCI. A loose neutral would only open the circuit
    ...
    a waste of time and money
    This is pretty much the response I was expecting from you.

    What makes a GFCI open is a perceived imbalance between the hot and neutral.

    In the perfect world, there would be no difference between theory and practice, but some of us can tell the difference.

  8. #8
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by LLigetfa View Post
    This is pretty much the response I was expecting from you.

    What makes a GFCI open is a perceived imbalance between the hot and neutral.
    Nothing percieved about it. The little current tap in the GFCI device MUST have a difference in current (not voltage) of between 4 to 6 milliamps before it will open, plain and simple.

    Quote Originally Posted by LLigetfa View Post
    In the perfect world, there would be no difference between theory and practice, but some of us can tell the difference.
    If you think that an induced voltage from a motor somewhere in a system starting or stopping will trip a GFCI receptacle then you ain't one of those who can tell the difference

  9. #9
    Moderator & Master Plumber hj's Avatar
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    I have seen MANY drinking fountains, freezers, and refrigerators which trip GFCI's.

  10. #10
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by hj View Post
    I have seen MANY drinking fountains, freezers, and refrigerators which trip GFCI's.
    I have never seen any appliance trip a GFCI device unless there was something wrong with the appliance.

    The NEC has mandated that commercial kitchen receptacles have GFCI protection including the ones that supply power to refrigerators and freezers. Drinking fountains are now required to have GFCI protection.

    210.8(B) Other Than Dwelling Units. All 125-volt, single-phase, 15- and 20-ampere receptacles installed in the locations specified in (1) through (5) shall have ground-fault circuit-interrupter protection for personnel:
    (1) Bathrooms
    (2) Kitchens
    (3) Rooftops
    (4) Outdoors

    422.52 Electric Drinking Fountains. Electric drinking fountains shall be protected with ground-fault circuit interrupter protection.

    If the appliance is tripping a GFCI device then it is time to call the repair man.

  11. #11
    Moderator & Master Plumber hj's Avatar
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    quote; I have never seen any appliance trip a GFCI device unless there was something wrong with the appliance.

    You haven't been in the right places then. I had one customer who had a freezer in the garage with an extension cord to it. When I inquired why, since there was an outlet next to it, they said it had "failed" while they were on vacation and ruinded the entire contents. I told her that there was a GFCI somewhere which had tripped. While searching for it, I found it in the bathroom UNDER a bench, and they had not even known it was there. The same thing happened to my daughter and as she said, "cleaning it up was a nasty chore". An elementary school which I was associated with would have to reset GFCIs when the water fountains had warm water. All of these worked properly after resetting the GFCI, so it was not likely to be a "failure" in the appliance.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    What most are calling a failure is really a failure in design. A properly designed unit will not trip a gfci unless it has become defective (and this does not mean it isn't preforming its intended task - it's just no longer totally safe doing it). The newer devices are designed with this in mind...older stuff, you're at risk. If you buy a new product and it trips, get it fixed under warranty, or have it replaced.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Plumber jimbo's Avatar
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    Many of us have seen the issues hj talks about. I don't think it can usually be attributed to a fault in the appliance.

    What I don't know is this.......are GFI receptacles today a little "smarter", so that for example motor load surges or whatever will not cause phantom trips??

  14. #14
    Electrical Contractor/Instructor jwelectric's Avatar
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    Every year new technology is being brought forth that improves everything including GFCI protection. In the early days of GFIC there were many issues with them including a high amperage trip of 100 milliamps or more.

    What causes a GFCI device to open is a difference in current and induced voltage will not and has never caused any GFCI device to open although those who do not understand the integral makeup of the device will tend to blame any and everything they can think of for a reason.

    The chip on the inside of a GFCI device will have two little current tap coils that constantly monitor the current in the two conductors. When there is an imbalance of between 4 and 6 milliamps between the two conductors then the device opens.
    These current tap coils cannot and do not read the voltages but do read the current or amps flowing in the conductor. If an induced voltage is in one conductor and does not complete the path to the other conductor then no current will flow the device will not open. If an induced voltage is induced in one conductor and there is a complete path then both conductors will carry the same amount of current imposed by this induced voltage and the device will not open.

    For the past 10 years or so if an appliance tripped a GFCI device then it was a fault in the appliance that caused an imbalance in current or in other words it was a defective appliance. This is not to say that when this fault occurred it did not clear itself and no longer is faulting and the appliance is working fine now.

    When the GFCI device is somewhere upstream of the appliance such as a breaker in the panel or a receptacle up stream it is very possible that the wiring between the device and the appliance being served was where the fault occurred.

    It is the job of the GFCI to keep someone from being hurt by electrical current. At around 2.5 milliamps a person can feel the current and it might be uncomfortable. At 25 milliamps a person is at their let-go threshold and in very much pain. The GFCI device is designed to open somewhere in between these two or at 5 milliamps. Notice that in this paragraph I made no mention of voltage but only addressed amperage.

  15. #15
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by jwelectric View Post
    Notice that in this paragraph I made no mention of voltage but only addressed amperage.
    You certainly do like to spit hairs and hang on the literal word.

    Can you have current without voltage?

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