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Thread: Breaker Won't Trip, Is It Bad?

  1. #1
    DIY Senior Member Briandl's Avatar
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    Default Breaker Won't Trip, Is It Bad?

    Recently some wires in the light for our ceiling fan started arcing, it generated so much heat that it burned through the metal (Aluminum?) of the light fixture itself. You could hear very loud popping noises when it was arcing.

    I took care of it by removing the light fixture (For now until we either get a new ceiling fan or a new light fixture).

    My question is, why didn't the breaker trip, and is that an indication that it may be bad?

    TIA

  2. #2
    Extreme DIY Homeowner Scuba_Dave's Avatar
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    Arc fault breaker will detect arcing & shut off
    If you know what else is on that circuit load it up to test
    Make sure it trips when capacity of the breaker is surpassed
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    DIY Senior Member TedL's Avatar
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    What's the brand of breaker/service panel?

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    DIY Senior Member Briandl's Avatar
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    I don't know off hand, I just assumed that normal operation of a circuit breaker is that it would trip if something connected to it arced.

    It sounds like you are saying proper operation is for it simply to trip it the load is too great for the breaker.

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    In the Trades maintenanceguy's Avatar
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    I certainly can't tell from here what was going on inside the fan but it's possible that you had arching that wasn't drawing more current than the breaker was designed for and therefore the breaker should not have tripped.

    A high resistance fault will cause a spot that can get very, very hot but still won't trip a breaker. The only way to know is to use an amp meter and let it arc while you check the current draw.

    If I was worried, I'd swap out the breaker when I replaced the fan.

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    DIY Senior Member Briandl's Avatar
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    Quote Originally Posted by maintenanceguy View Post
    I certainly can't tell from here what was going on inside the fan but it's possible that you had arching that wasn't drawing more current than the breaker was designed for and therefore the breaker should not have tripped.

    A high resistance fault will cause a spot that can get very, very hot but still won't trip a breaker. The only way to know is to use an amp meter and let it arc while you check the current draw.

    If I was worried, I'd swap out the breaker when I replaced the fan.
    That sounds about right.

    I took out all of the sockets from the fixture and the insulation around the wires was gone near the sockets, which caused the arcing.

    Am I correct in assuming this is from the heat generated by the bulbs?

    I've always assumed that which is why I consider the fact that CFL's run much cooler than standard incandescent bulbs to be another advantage of using them.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you don't exceed the wattage specified for the bulb sockets in the fixture, you should not be generating too much heat to create a problem. Putting say a 100W bulb where it says 60W max could create a problem. The wiring is rated at a specific temp, and there's a safety margin if you follow the instructions, nothing should happen.

    Think of an arc welder...lots of sparks, won't trip the breaker. Depends on how much current is being drawn. As mentioned, that sort of thing can still create a fire hazard, and is one reason why they now specify arc fault detector breakers for bedrooms - they are designed specifically to trip when that sort of thing happens.
    Jim DeBruycker
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    DIY Senior Member Briandl's Avatar
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    For as long as I can remember they (my in-laws) have been using 60 watt bulbs which is the max recommended. I suppose it's possible that something else was used at some point in the past.

    Other than that, what else could cause this:


  9. #9
    Extreme DIY Homeowner Scuba_Dave's Avatar
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    Green - looks like corrosion/oxidation too
    Is this really old?
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  10. #10
    DIY Senior Member Briandl's Avatar
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    I just assumed that was bound to build up since the insulation was gone.

    It's probably about fifteen years old but that's just an educated guess.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Looks sort of like it got wet.
    Jim DeBruycker
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    DIY Senior Member TedL's Avatar
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    Standard circuit brakers will not trip simply due to an arc. That's why there are the relatively new Arc Fault Circuit Interrupters, which do trip in that circumstance.

    You want to make sure that you do not have Federal Pacific Electric (FPE) breakers and panel. A high % do not trip when they should; they also have other well documented problems. Serious stuff. Please take the 60 seconds to look at the panel.

  13. #13
    Moderator & Master Plumber hj's Avatar
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    Default arc

    An arc is not a short circuit. That is why arc welders can work as long as you do not touch/weld the electrode to the workpiece.

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    In the Trades maintenanceguy's Avatar
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    From the picture of the socket, I'd say the wires got too hot. Either too big a bulb was used, air flow around the wires was restricted, or the fixture was designed and manufactured poorly. Since it's only melted on the very end, near the terminal screws, it could be a loose, corroded, dirty connection at a screw. Bad connections causee high resistance and hot spots that will heat up the copper wire within a couple of inches of the bad connection.

    Once the insulation is gone, the copper is exposed to the air and pretty hot so it oxidizes quickly.

    If you're married to this fixture, there's high temperature wire available to re-wire it. I'm not sure what the covering is now but it used to be a fabric asbestos material. I still ask for "some of that asbestos high temp wire" and they know what I want.

  15. #15

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    why didn't the breaker trip, and is that an indication that it may be bad?
    It MAY be an indication of a bad breaker but probably not.

    A standard breaker is designed to take a bigger load for a short time. I have seen many temporary shorts that didn't trip the breaker.

    The burned wiring is simply from the heat from the lamp over the years. It's a very common occurance.

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