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  1. #1
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    Following code to a fault

    How would one determine this problem ? Two identical 120 volt fed control panels wired with exactly the same terminations. The first on gets plugged in to a temporary power supply to warm the compressor and oil heaters and works fine. The second panel gets a temp. hook up and trips the GFCI plug. The panel wiring is checked, checked and re-checked with the same results. The temp. power from the first panel is swapped to the second panel and it trips that GFCI. Both panels are 120 volt. With all power removed both panels are compared to each other with resistance readings all the same. As these are 120 volt circuits the ground get removed during the check-out. On the panel that is tripping all loads are checked individually through the GFCI plug and it stay online. All the loads are disconnected as in the previous test and the panel is plugged in again, the GFCI again does not trip. Put everything back together and it trips, just like before. Then the same panel is plugged in to a temp. power cord that has been fused and plugged into a standard 20 amp wall plug. It stays online, the fuse remains intact and all is well. I do realize that it only takes a very small amount of current bleed to cause a GFCI to trip, but what am I missing ? Appreciate any help or answers. -GEO
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  2. #2
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    Maybe because I've been up for 18 hours, spent 7 of them in a steam class, followed by a two hour CM test, but...

    I'm confused.

    Could you maybe give me a more complete description?

    Have you tried a different GFCI? Is it an outlet style or panel breaker style?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  3. #3
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    A GFCI detects 3-5 ma difference in current btween line and neutral. That can be anything going to ground or whatever - just an imbalance. If your meter is not accurate enough to read 5 ma you may not pick it up.

  4. #4
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    AND... GFCI outlets have a 10% failure rate out of the box. Not many folks know what they are getting. An external tester for these circuits is a good idea, too.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  5. #5
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    Jan 2005
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    This is an outlet style GFCI. Actually a temp. construction panel as the customer does not want any in house wall plugs used unless absolutely necessary. I think I can rule out a defective GFCI as one panel has not tripped the ground fault, but the other panel does. I am more inclined to think about the current leaking from the neutral to ground, as these outlets are extremely sensitive and more so then others. That why I put this post in the new electrical forums as I was hoping to hear from someone in another trade with their history of this problem. I have seen this issue several times before and when plugged into a regular 20 amp outlet the problem disappears. It just when you have several thousands of dollars worth of electronics on a new piece of equipment you tend use a little more care and not want to take chances.-GEO
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  6. #6
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    In that case, the first thing I would check is the main bonding jumper.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  7. #7
    Join Date
    Feb 2013
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    Florida
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    The gfci is measuring current on the load side of the gfci, so I would be looking at the loads you are plugging into the one that is tripping. Any kind of electronic ignition device will cause a gfci to trip as well as some rectified circuits that run to ground

  8. #8
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    Another thing to look for is if your neutral is grounded in more than one location. I have run across some panels where whoever connected it, treated it like a service panel and grounded the neutral there and making a parallel neutral back to power supply.

  9. #9
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    Quote Originally Posted by bkmichael65 View Post
    Another thing to look for is if your neutral is grounded in more than one location. I have run across some panels where whoever connected it, treated it like a service panel and grounded the neutral there and making a parallel neutral back to power supply.
    Good point.

    A neutral grounded in a place other than the service panel causes "objectionable current." I would check for any other connections between neutral and ground, as well.

    If you connect the loads one at a time, the load that causes the trip could reveal the circuit with the problem, couldn't it?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  10. #10
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    Jan 2005
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    Houston TX
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    Timebuilder- As I said in a previous post I can plug in the loads, in this case oil and compressor heaters, 6 altogether totaling about 12 amps, directly to a 12 gauge grounded cord and they work fine on the same GFCI as the one that trips. When the heaters are wired back into the compressor control panel, the same GFCI will trip. At this point in the compressor control panel the heaters and feed (120 volt) to the oil pump (not energized) are the only thing on the control.-GAB
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  11. #11
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    May 2011
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    Can you possibly draw one or two diagrams to show what you mean?

  12. #12
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    Quote Originally Posted by ga1279 View Post
    Timebuilder- As I said in a previous post I can plug in the loads, in this case oil and compressor heaters, 6 altogether totaling about 12 amps, directly to a 12 gauge grounded cord and they work fine on the same GFCI as the one that trips. When the heaters are wired back into the compressor control panel, the same GFCI will trip. At this point in the compressor control panel the heaters and feed (120 volt) to the oil pump (not energized) are the only thing on the control.-GAB
    I am probably not making my question clear. my bad.

    Can you plug in the loads one at at time? What happens then? Can you associate one load being connected with the tripping GFCI?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  13. #13
    Is there a control transformer in the control panel ?

    Current leakage , which will trip a GFCI is cumulative , as some one has said . You are feeding 2 sets of heaters ? If so , disconnect one , then the other ?

    God bless
    Wyr

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