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Discussion Starter · #1 ·
This is residential. I have a breaker (20 amp) that controls a double detached garage. The wiring running out to the garage is buried in conduit.
Each garage has an overhead electric opener, a switched ceiling light (1 single bulb), and 3 wall sockets.
Yesterday it got extremely cold for the first time this year, about -12 F or so.
The breaker popped, but could be reset. All power in the garages was off, whether the breaker was on or off. I checked the breaker with a volt meter, and no juice was coming through it. It seems to be dead.
I replaced the breaker with another 20 amp breaker, and confirmed that it was passing juice through when it was in the on position.
When I attach the wire that runs out to the garages to the breaker, it immediately pops it. It won’t stay in the On position.
There was a space heater plugged in the garage, as well as a big garage light. Both were running when the original breaker went bad and everything died.
I unplugged everything, and gave it another shot, but the breaker still won’t stay in the On position. I checked all the wall sockets and light bulbs, and everything looks to be in good condition in the garage.
I took out the 20 amp breaker and replaced it with a 50 amp, just to see if it would hold or not. After connecting everything I (very briefly) turned on the 50 amp breaker. The garage did have power, and the breaker did not pop itself off. I only left it on for a few seconds, as it’s clearly more juice than the wire can handle (it warmed up pretty quick).

Has anyone seen anything like this? It seems like there’s a short somewhere, but if that were the case wouldn’t the 50 amp breaker pop as well? Perhaps this replacement breaker is faulty as well? Any advice is greatly appreciated.
 

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A "Handy Husband"
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It sounds like a high resistance short in the underground cable. Disconnect the cable in the garage with the breaker off and test the resistance with a multi meter. From the hot conductor to ground should read infinite resistance (in the meg-ohms).

What type wire or cable is in the underground conduit?
 

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I agree with rjniles... This sounds very similar to what i was experiencing with my detached garage - only during the period of an initial major temp swing (i.e. first big ground freeze in early winter, and then thawing-out time in spring - I'm in MN), my garage would pop the breaker - I could usually get it to reset, but the problem just got worse (happen more often) every year.

Two years ago, I finally ripped up all the old underground cable (it was in pretty terrible shape) and replaced that whole line (from the main panel in the house out to the garage). Things have been flawless since.

Cheers, Chris
 

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Funny thing about breakers; they tend to trip when overloaded. Not sure what the length of cable to the garage is but between the 1500 watt draw of the heater plus old insulation I think the breaker was telling you something. Circuits overloaded or there is a short. I am no mechanic ( left the car repair to other guys years ago), so my garage requirements are minimal. But I would put more than a single 20 amp circuit to a detached garage. Two 15s or two 20s especially if a heater was involved.
 

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Discussion Starter · #7 ·
Ok. I'll check that resistance. Thanks for the advice rj. It's 12 ga romex out to the garage.

Thanks Chris too. I'm hoping to avoid that ripping up thing as this wiring runs under 20 to 25 feet of asphalt!

Joe and dmx, I don't think the wire is cooked out. I only had it on for a second or two. It got warm for sure, but not hot. I followed it through the basement, and it didn't smell burned, nor was there any melting at the breaker box or a junction box in the basement where they're exposed. I completely agree that it was a really bad idea. Hopefully I'm alright in that regard.

Jim, I agree completely. Could be time for an upgrade to the old system here. Really don't want to dig up all the asphalt, but it may be the only option I guess.
 

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A "Handy Husband"
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If it is really Romex then we may have found the issue. Romex is not rated for use in underground conduit. If you have conduit, you should be able to pull out the old and pull in new. What is the size of the conduit? Plastic or metal?
 
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Discussion Starter · #9 ·
Sorry for the delay. I've been crazy tied up at work, and up until today it's been crazy cold out.

I was able to find where the wires leave the house and head out to the garage, as well as enter the garages and supply power for each.

The wire going outside is gray, about 1 1/4" to 1 1/2" wide, and has a white, black, red, and ground wire in it. The sheathing is solid gray plastic. Sorry I don't know what this is called, but it seems like the appropriate type of wire to bury.

The black wire and the red wire are both wired to different 20 amp breakers. When you track it out to the garage you can see that each garage is on it's own 20 amp breaker, because the black wire feeds power to one side and the red feeds power to the other. When I disconnect the garage feed wires for both garages in the junction box that is in the garage and turn both breakers on, everything holds just fine.

I can test the hot wires and see that they're both supplying what they should.

I can connect one garage to it's feed wire with no issues. It's breaker holds, and everything works.

When I connect the other garage's main line to the hot line and turn on the breaker, it pops it every time. Won't stay on at all. Same goes for if I wire both garages up to the same 20 amp breaker (that works for one garage just fine). Seems to indicate that there's a short somewhere in the other garage.

Does that estimation sound accurate based upon the new data?
 

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When I connect the other garage's main line to the hot line and turn on the breaker, it pops it every time. Won't stay on at all. Same goes for if I wire both garages up to the same 20 amp breaker (that works for one garage just fine). Seems to indicate that there's a short somewhere in the other garage.

Does that estimation sound accurate based upon the new data?
You narrowed it down! Your fault is in that half of the garage. Now unplug all appliances, turn off all switches, and disconnect any other loads and try again. If it holds, then the problem is with one of the devices. If it trips, then the problem is with the wiring itself. You'll then start opening boxes and disconnecting things until you've found the culprit. It will either be a bad device, or a damaged wire.
 
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