short in wiring

plato319January 18, 2013

I recently put new siding on my garage.I just noticed that the last 2 months my electrical bill has more than doubled. After some troubleshooting I found the problem is a circut in my garage breaker box is pulling between 700 to 1000 watts with nothing but a 13 watt cf nightlight hooked to it. Is it possable for a nail from the siding to be shorting a wire and use this much power without causing a fire? I shut down the circuit, anyone have any ideas how to pinpoint the problem spot? The garage is insulated and drywalled

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You registered today. The reported high wattage (??) draw is suspicious in that you do not report any tripped breakers or blown fuses. We are not told how you measured this high wattaqe (??) draw. The significant lack of other information hampers any attempt to help. So the panel and the affected conductors are in the garage only? The circuit serves nothing outside the garage? How many outlets (receptacles, lights, etc. ) on this circuit? Remember, we are not there to look at it, yours are the only eyes on-site. Do the conductors go around any corners of the garage? Don't be stingy with information and perhaps someone will be generous with advice.

    Bookmark   January 18, 2013 at 8:07PM
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Thank you for responding to my post. I have visited this site off and on for years.
I will try to answer your questions. I narrowed the problem to the garage by checking my meter spinning wheel with the garage breaker turned on and then off and noticed a huge differance in speed. I then narrowed it down to this circuit. With this circuit engaged the wheel takes 10.7 sec to make a revolution and when off it takes 44 secs. my meter has 4 dials and a kh of 3.6. My bill was always about $70.00 in winter and now its $170.00 with no other changes in my usage.
There is another circuit that instantly trips when reset. I dont know what it controls. The circuit in question has two switches one by each door and is connected to a 13 watt yardlight that is mounted on the end of the building. I dont know the route the wire takes as the walls are drywalled.
I found my fluke bk clamp-on meter with ir temp sensor today and was wondering if i could use it to check for any temp spikes on the walls. Any ideals on my problem are welcome

    Bookmark   January 19, 2013 at 4:44AM
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New siding? What material? Some siding material is rather easily removed and reinstalled, some not easy at all.
It looks as if an experienced electrician at your premises will be needed to diagnose and repair this problem.

    Bookmark   January 19, 2013 at 7:17AM
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Is there anything on the circuit that was forgotten about? Lights in an attic space? Electric heater that is turned on? Any outbuildings like a shed that could get power from that circuit? Dusk to dawn lights that have a bad photocell and stay on continuous? Refrigerator or freezer?

    Bookmark   January 19, 2013 at 10:30AM
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It is possible, but rare, to manage to hit a cable and create a load that is not large enough to immediately blow a breaker.

If the siding has concealed fasteners the problem gets very hard to locate the actual point, though there should be a decent amount of heat being generated creating a warm spot on the siding that should not be hard to find with a bare hand.

A clamp on ammeter would be a better tool to determine what circuit is pulling power.
Once you know the circuit just turn the breaker off and see if the current drops to zero.

    Bookmark   January 19, 2013 at 1:17PM
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My money is on a nail into some NM cable. It wouldn't surprise me a bit. I can't imagine there are too many circuits running inside the walls of the garage, unless it is a workshop with lots of receptacles. After turning off power to the garage, open the panel to check for nails into the back of the panel tub. You have already identified the circuit. Check all known receptacles, switches and light fixtures. If that turns up nothing, just follow the logical path from point A to point B and start digging in. If this is above your comfort/skill level, call a reputable electrician for assistance.

    Bookmark   January 19, 2013 at 3:20PM
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Pretty hard to make a connection that is not tight enough to trip a breaker, but tight enough to dissipate "700 to 1000" W.

    Bookmark   January 19, 2013 at 5:35PM
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I checked this circuit out again today. On its way to the light it has 2 outlets then a 3 way switch, from there it goes above the garage door to the light near the peak at the end of the building and then to another switch by the other walk in door.
I can pull the first outlet out and check if I've passed the bad spot and if not I'll move-on to the next one till I pinpoint the area. Then I will cut holes in drywall near each stud till i find the short. How does that plan sound?

    Bookmark   January 19, 2013 at 6:35PM
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Golly by Gosh, if it is a nail, just walk around at night and look for a nail head glowing cherry red!

Seriously though, I read your last post but I'm not sure how you plan to identify which part of the run is causing the problem. Are you going to disconnect the wiring in each box along the way and run back to check the meter?

Get a clamp-on AC amp meter - the can be found in the box stores starting at around $50-70.

First, if you are comfortable taking the cover off your panel to access the wiring, clamp it around the hot lead coming from the breaker and it should read around 5-8 amps of current for the wattage you're indicating.

Next, since this sounds like the wiring is NM, clamp it around the whole NM cable before it exits the panel. This will tell you if you are looking for a leakage within the cable or a ground fault. "Zero current" is within the cable since the hot and return cancel on the meter. If you do get a current reading, the leakage is from the lead hot in the cable to an external ground somewhere.

From there, go from box to box, pull out the receptacle and just clamp around the hot lead and measure current. When you get to zero current, you know the problem is between that box and the previous box.

This post was edited by yosemitebill on Sat, Jan 19, 13 at 22:07

    Bookmark   January 19, 2013 at 10:00PM
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Ron Natalie

YBill is right except that if the fault is bridging the hot/neutral rather than touching the ground (either within the cable or external), the meter will still read a zero sum accross both (and even a GFCI won't trip).

    Bookmark   January 20, 2013 at 12:11AM
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Thanks for the info Ybill. I have a clamp on meter. I tried it on the circuit and it reads about 8 amps. Your info about checking the outlets is helpful. I put vinyl siding on the building and I cant see the nails and dont want to tear it off Id rather cut the drywall to fix the problem.

    Bookmark   January 20, 2013 at 7:12AM
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Ron Natalie

8 AMPS? You have a serious ground fault somewhere.
Your hot is leaking substantially to ground and not to the one in the cable.

You'll have to divide and conquer. Try the meter at various places in the circuit that are accessible and see if you can find the segment with the problem.

    Bookmark   January 20, 2013 at 8:33AM
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If the nail heads are exposed you can just walk around with a volt meter and use the ground from an extension cord.

One of the nail heads is going to read pretty close to 120 V.

Ground from the ground prong of the plugged in cord, other meter lead on the nail head.

The problem occurs with concealed nail heads.

In that case you should be able to easily feel the warm spot.

8 amps is right around 1000 W in a 120 V line.

Plenty of heat to feel.

    Bookmark   January 20, 2013 at 9:25AM
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I'm thinking a non-contact voltage tester might be useful. At least with vinyl siding, running it along the siding a the location of the nailing slots should be close enough that a "energized" nail should set it off.

Although I'm trying to envision a typically constructed garage using NM cable that would allow a nail touch the hot wire in the cable AND hit something else that would provide a path to ground outside the electric system. Certainly wood at 120v wouldn't do it. A water pipe?

    Bookmark   January 20, 2013 at 9:02PM
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I pulled out the switch and disconnected the wires exiting it ,no change, so I disconnected the wires on the closest outlet. i had 125 volts on supply side and 63 volts on exit side that should be 0 volts. Then I reset the 2nd circuit that previously would instantly trip, Now it stayed on and the outlet that had 63 volts has 125 volts.The problem curcuit is now pulling 5 amps instead of 8 . I seem to have 2 circuits cross shorting. Im going to purchase a stud sensor today that detects voltage so i can pinpoint the area that the cables cross the studs. I think a nail is pentrating two cables and causing weird stuff. Whats your opinions?

    Bookmark   January 21, 2013 at 8:45AM
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Ron Natalie

That's a possibility although be very careful in what you think you're measuring. Many digital meters are of such a high impedance that they will measure induced current on wires that are just open.

Ah, so there's been another affected circuit which keeps tripping the breaker?
So nice of you to omit pertinent details.

Any chance that other breaker was a GFCI? (In fact your receptacles in the garage should also all be GFCI protected). I suspect you do have a ground fault and possibly to the other circuit. The really annoying thing given a lot of shoddy harry homeowner work in the past is that it may be something stupid like an overzealous wholloping of the staple on the NM cable. The installation of the siding may not have put a nail into it but vibrated things enough to make the latent bad installation fail.

    Bookmark   January 21, 2013 at 9:04AM
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I did mention the 2nd circuit in a previous post. None of the circuits are GFCI. I did not install the main wiring. I think it was installed before GFCI was required by the previous owners electrician. I did add 2 double breakers for my air compressor and welder.

    Bookmark   January 21, 2013 at 10:51AM
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Ron Natalie

Given that one hard trips, I'd trouble shoot that one first. Again divide and conquer. Remove things from the circuit until it stops tripping.

    Bookmark   January 21, 2013 at 10:59AM
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Maximum diagnosis, minimum repair. The problem can be narrowed down to the area between two access points by competent diagnosis.
A nail into a conductor that results in a consistent amperage draw of about 8 amperes without causing a localized overheating of fire-causing-proportions and does not trip the overcurrent device? About as likely as as seeing roadside in upstate NY a cow sitting in a cactus singing like a canary. Or our leg is being pulled.

    Bookmark   January 22, 2013 at 7:26AM
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Ok, late night or early morning, when it's cool outside, use an infrared camera to find the hot spot, if there is one.

    Bookmark   January 23, 2013 at 1:53AM
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I cut some holes in the drywall yesterday and on the last stud I found 3 cables burned and melted together but I could not find any nails. Maybe it melted off. When I get them cut and replaced I'll update and let everyone know if its fixed or if I have other problem areas.

    Bookmark   January 24, 2013 at 8:55PM
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Thank your lucky stars your house didn't burn down.

    Bookmark   January 25, 2013 at 4:31PM
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Ron Natalie

It's possible whoever installed the siding hit the wires with a nail and pulled it back. With the insulation damaged they still could arc or have a high resistance connection.

    Bookmark   January 25, 2013 at 6:56PM
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Today I cut out and replaced about 10' sections of the damaged NM cables. I installed junction boxes at the splices. Happy to report that all is well. Now all I have to do is repair 7 holes in the drywall. I am very lucky my garage did not burn down. Thank you all for your help.
\ Gene

    Bookmark   January 25, 2013 at 7:19PM
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Make sure all of those junction boxes are accessible, not buried behind the drywall.

    Bookmark   January 26, 2013 at 10:52PM
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You're welcome, and we're glad you didn't have a fire either. Mind Btarmy's advice re the splices.

I'm guessing that wire wasn't done to code, if siding nails penetrated it, or they were really long. Probably a bit of bad luck too, often if it's not near a staple, the wire will just move.

    Bookmark   January 27, 2013 at 10:22PM
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