Troubleshooting Residential Short

larry1987February 12, 2012

Would love your suggestions regarding troubleshooting a short in a circuit at my house. After living here 20 years, one of the breakers continues to trip and once i tried to reset it, even sparks at the panel. I tried switching out the breaker for another breaker in the panel (shutting of main, carefully disconnecting wires to breaker, switching known good breaker for suspected "bad" breaker - same result. switched back to original configuration. Tested breaker with multimeter by touching screw with positive lead and ground buss bar with negative lead - multimeter read 120. This tells me breaker is good, yes? Next i disconnected all of the appliances from the outlets and disconnected all of the lights fixtures from the white & black wires from the ceiling boxes - breaker still trips. is there a way to systematically locate the short using the multimeter?? possibly testing each outlet pair of wires for resistance? thanks, larry

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bus_driver

Get a pigtail lamp socket. Remove the wire from the breaker and wire nut it to the white wire on the lamp socket. Put the black wire from the socket to the breaker, install an incandescent lamp in the socket, wattage is not important but 60 or less is recommended. Turn on the breaker. As long as the lamp lights, there is some sort of load (or short circuit) on that circuit. Start disconnecting the black ( or red) wire on that circuit one at a time at the device nearest the panel. If you work with the breaker on, there is 120 volts on the circuit-feeding through the lamp. I usually work them hot in cases like this but I do not recommend that others do so. Turning off the breaker while handling conductors and devices is safer- but slower. The problem will between the devices where the light goes out when the device is disconnected and when it does not go out when the device is disconnected. Disconnect only one at a time and reconnect it as soon as you know that the problem is somewhere else, then move to the next one, moving farther from the panel each time.
Most of the time, my suggestions are ignored. In most cases I do not try to help those people again.

    Bookmark   February 12, 2012 at 10:12PM
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larry1987

bus driver: wow - thanks for the detailed advice. I won't ignore your suggestions that's for sure. i might have some follow up questions but tomorrow I'm on my way to the electrical supply store for a pigtail lamp socket. thanks again. will let you know how it goes.

ps: i don't have your knowledge, experience or courage - i will be turning the circuit off in between tests per your suggest. thanks again. larry

    Bookmark   February 12, 2012 at 11:17PM
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kudzu9

bus_driver-
Just to let you know, even though some folks ignore advice from you (and others), it doesn't mean that there aren't a lot of us who appreciate your replies and learn stuff from many of them. Thanks...

    Bookmark   February 13, 2012 at 10:12PM
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ranger619

Lary, the short might be in a switch. taking the lights down might not solve that issue. If a switch is bad even if it is turned off ... can have a short in it. just something else to try. i have seen this before. see if you can follow the wire out of the panel that is shorting to its first location and try to start there. If it goes into an outlet then take that outlet apart and then try to reset the breaker..at least you can rule out that section of the feed.

    Bookmark   February 14, 2012 at 4:22PM
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larry1987

bus driver: sorry for the delay... I'm the classic definition of a "weekend warrior" so I'm only now putting your suggestions to work. I bought the pigtail lamp socket yesterday. Let me tell you my progress. just to test the breaker, I touched the black wire of the pigtail to the breaker screw and the white pigtail wire to the ground bus bar... The pigtail lamp light lit up for every breaker EXCEPT the breaker that I'm having problems with. On the "troubled" breaker the light didn't illuminate. That made me think the breaker was bad. I went to Home Depot, bought a replacement breaker, came home and attached the wire to the breaker and re-installed it... I then switched it on and it speaker and kicked off... OK i have a short somewhere. Using my multi meter to check for continuity, i disconnected the wire from the breaker, I touch the red lead to the screw of the breaker and the black lead to the now dangling wire - the continuity alarm sounded - I then touch the black multi meter lead to the ground bus bar and the continuity alarm sounded again.

I then - per your suggestion - used a wire nut to connect the white from the pigtail lamp to the wire from the breaker and the black wire from the pigtail to the screw of the breaker... i switched on the breaker, and the light stays on... I thought the breaker would kick off and short out but it didn't.... hmmmmmm... does that sound strange to you? while I'm typing this, the light of the pigtail lamp continues to be lit. I am now starting to open up the outlet closest to the panel. Let me know if you have any thoughts/suggestions regarding what i've done thus far.

thank you very much in advance. larry

    Bookmark   February 18, 2012 at 3:58PM
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larry1987

Ranger619: thanks so much for the suggestion. Will let you know how it goes shortly. larry

    Bookmark   February 18, 2012 at 4:00PM
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bus_driver

The lamp limits the current to just a fraction of an ampere. With the lamp in place, any current on that circuit must flow through the lamp. It will be far too small to trip the breaker or to cause a major spark or additional damage to the wiring. But keep in mind that the voltage on that circuit is still the full nominal 120 volts. The first test you did, not part of my suggestion, did not accomplish anything as far as I can see.

    Bookmark   February 18, 2012 at 5:25PM
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larry1987

Ranger619: thanks so much for the suggestion. Will let you know how it goes shortly. larry

    Bookmark   February 18, 2012 at 5:41PM
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larry1987

bus driver: thank you for the follow up. Question: is the lamp supposed to go out at some point? i've taken apart several switches and outlets and the pigtail lamp remains on. Am i doing something wrong? thanks!

    Bookmark   February 18, 2012 at 6:01PM
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brickeyee

As long as the lamp remains on something is pulling current in the circuit.

If the bulb is fully on there is a short, if it is dim there may be another load on the circuit but it is not a short (the bulb any any load on the circuit are in series, so neither has enough voltage for full operation unless the load is very large).

    Bookmark   February 19, 2012 at 1:34PM
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bus_driver

In my first response, I assumed a higher level of existing electrical knowledge than is now apparent. Go back and read my first response. "The problem will between the devices where the light goes out when the device is disconnected--"
Also as I stated, disconnect devices ON THAT Circuit. To determine what is on that circuit, turn off the breaker that has been tripping and leave all the other breakers on. The things that do not work under those circumstances are on the problem circuit. OK? The only way things could be disconnected and the bulb still be lighted is if the problem (1) is between the panel and the first device after the panel, or (2), the devices being disconnected are on a different circuit.

    Bookmark   February 19, 2012 at 9:08PM
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hrajotte

It is unusual - but not impossible - for a short to occur for no apparent reason. Has any work been done that may have caused physical damage to a wire? Siding installed? Insulation stapled in? New windows? Anyone bang a nail in the wall to hang a picture? Install any luan/new flooring? If so, try to focus on the work area, that's probably where the short is.

    Bookmark   February 21, 2012 at 10:40AM
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countryboymo

FYI this same technique works on your car with a test light. Remove a battery cable and put the test light between the cable end and the battery terminal it is supposed to be on. If the light illuminates there is enough draw to kill the battery. Pull fuses until the light goes out and then look investigate what is on that circuit.

Didn't mean to go off topic... just a morsel of helpful information.

    Bookmark   February 22, 2012 at 6:43PM
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bus_driver

With vehicles, using a voltmeter is much better than a test light. Some unwanted current draws on vehicles are too small to cause the test light to be visible. Can't fool the voltmeter.

    Bookmark   February 23, 2012 at 9:33AM
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