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Thread: Mhysterious circuit problems.

  1. #1
    DIY Junior Member
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    Default Mhysterious circuit problems.

    I have a 20amp circuit that once in a while it goes out, does not trip the breaker and a day later comes back on by itself. I disconnected all appliances and removed a gfci breaker, reset the breaker and nothing. I disconnected the hot from the breaker and did a voltage test between the breaker terminal screw and the neutral bar. It reads 118v. I reconnect the hot lead and did the test between the breaker terminal screw and the neutral bar and it reads 2.4v. I move the breaker to another location and did it all over.. Same results. I got a new breaker and repeated the above tests with the same result. A few people mentioned an open neutral.
    Even if there was an open neutral, should the voltage reading between the breaker terminal screw and the neutral bar still real 118v?

  2. #2
    Homeowner Thatguy's Avatar
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    Make all your voltage measurements while the circuit is loaded with a 10 A load - a toaster or a hair dryer.

  3. #3
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Thatguy View Post
    Make all your voltage measurements while the circuit is loaded with a 10 A load - a toaster or a hair dryer.
    Why??

    What does a toaster or hairdryer have to do with voltage?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    A GFCI breaker has a neutral pigtail that must be connected to the neutral bus bar to function properly (at least on the few I've dealt with). If that lead is disconnected, it won't work. Then, the hot and neutral from the circuit it is protecting get connected to the GFCI breaker.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
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    I actually seem to have isolated the problem somewhat.. It occurs on just 1 side of the panel circuit. Oddly, there is measurement of 118v from the bus bar to the neutral bar, but none of the breakers on that side of the bar will work. I measured the main coming in on that side of the bar and it was 118v.

  6. #6
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    See my other posting on what i found.. But problem still not resolved.

  7. #7
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by mikecq View Post
    See my other posting on what i found.. But problem still not resolved.
    At this point I would try to figure out the wiring in your load center. It's not easy because the breakers cover up the busbar routing.

    Your 2.4 v reading seems to be still unexplained. Generally it's too low to be a phantom voltage.

    You can check for a bad neutral.
    Put a 10 A load on one outlet and measure the voltage on each side of the neutral. If it's 130 v and 100 v then there must be about (130-100)/2 = 15 v across a neutral connection that should read only millivolts.
    Last edited by Thatguy; 12-14-2010 at 01:48 PM.

  8. #8
    Test, Don't Guess! cacher_chick's Avatar
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    Check the wire for line voltage when it is disconnected from the breaker. It could be backfeeding from another circuit.

  9. #9
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    Problem solved.. A bad 100amp fuse outside at the meter. The original installer did not use die-electric grease so it started corroding. This caused intermittent outages.
    Tough one to track as only 2 breakers were on that leg of the circuit. The other breaker was never noticed as it was in a laundry closet and never used, so it seems like only 1 breaker was at fault.
    Thanks to everyone for their input.
    Hope this helps everyone in the future with similar problems.
    Last edited by mikecq; 12-14-2010 at 04:05 PM.

  10. #10
    Test, Don't Guess! cacher_chick's Avatar
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    Reading your prior post I realized my previous reply would not be correct. This would be a case where loading the circuit might have been beneficial to testing. There are no outside fuses or breakers used for residential here in the great white north, so so I will have to keep that in mind for future reference.

    Glad to hear your problem has been resolved.

  11. #11
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by mikecq View Post
    it started corroding. This caused intermittent outages.
    The thing must have gotten pretty hot when your current demand was high.
    2 v x 50 A = 100 W dissipated in just this one bad connection. If the fuse holder didn't get baked the springy clips might have lost their tempering and so the holding force is much less and the contact resistance at the interface between the fuse end and the clip is much higher.

    I recommend turning on several appliances and measuring the voltage drop between the fuse end and the clip. More than a few millivolts may cause trouble down the road. The fuse clip manufacturer may or may not provide you with pass/fail specs for this contact resistance.
    Last edited by Thatguy; 12-15-2010 at 10:20 AM.

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    General Engineering Contractor ballvalve's Avatar
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    I am the di- electric grease and paste advocate! And I have been attacked for that in the past.

    I think it should be the pipe dope of electricians.

    Saw hundreds of cooked and oxidized connections that 2 cents of paste would have cured years earlier.

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