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Old 01-10-2011, 12:50 PM   #1
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Breaker Keeps Tripping


I have a 500 sq ft MIL unit behind my house that was built in 1951 and it is on its own electrical meter. The meter and main panel is on the side of my house and then wire is running overhead to the attic of the MIL unit. The crazy part is that the main panel only has one 20 AMP breaker for the entire unit! Then there is a sub panel in the closet with three 20 AMP breakers. From what I can see it looks like the wiring is older 2 wire romex.

My problem is that when NO ONE is home the 20 AMP breaker at the main panel keeps tripping, but none of the breakers in the subpanel are. I replaced the breaker thinking maybe it went bad but it is still doing it. I had a electrician come out and he said that since nothing is running except the fridge when no one is home, the fridge could be wearing out and holding a load and then releasing it causing the breaker to trip. Does this sound right? If so, shouldn't one of the breakers at the subpanel trip before the breaker at the main panel?

If it's not the fridge, what else could cause this?

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Old 01-10-2011, 03:30 PM   #2
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Breaker Keeps Tripping


if you suspect the fridge, can you run an extension cord from the fridge to another circuit fed by the one of the other breakers. It should trip that breaker if it is the culprit. also, i assume that the sub-panel is not fed by the single 20amp breaker which then has (3) 20amp breakers...

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Old 01-10-2011, 04:16 PM   #3
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It could be the fridge and the upstream breaker is just winning the race to trip.

More likely IMO is that there is a problem with the overhead wiring, from whipping in the wind. Check for damage, near points of support. If wire is big enough you could up size breaker. Could you plug the fridge in to the house via extension cord?
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Old 01-10-2011, 04:20 PM   #4
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Breaker Keeps Tripping


I could run a cord to another outlet, but it's not tripping any of the breakers in the subpanel in the closet, only the main 20 AMP breaker outside is being tripped. So I don't think that would narrow anything down.

What your saying about the single 20 AMP breaker at the main panel feeding the other three 20 AMP breakers in the subpanel makes sense. I bought the house like this with the 20 AMP breaker on the main panel. I wonder if perhaps the main service could be larger than 20 AMP's but someone just put in a 20 AMP as a replacement if an older breaker needed to be replaced. The wire at the main panel looks thicker than 12-2 wire. What do you think?
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Old 01-10-2011, 04:47 PM   #5
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Breaker Keeps Tripping


How would I determine the size of the wire at the main panel and if I could put a larger breaker in to replace the current 20 AMP breaker?
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Old 01-10-2011, 04:47 PM   #6
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I could run a cord to another outlet, but it's not tripping any of the breakers in the subpanel in the closet, only the main 20 AMP breaker outside is being tripped. So I don't think that would narrow anything down.
Well what I have seen happen a lot is a breaker in a sub panel that should trip and only effect one circuit, gets beaten by a breaker in a main panel that shuts a whole plant down. Moving the fridge to a house circuit would allow us to see if it trips the house plug, if it did then we would blame the fridge and another case solved. However I suspect something else, which is why I would like to see if it still trips even if nothing is in the shop.
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Old 01-10-2011, 04:49 PM   #7
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How would I determine the size of the wire at the main panel and if I could put a larger breaker in to replace the current 20 AMP breaker?
is it labeled? Do you have a section of #12 that you could compare it with? Be careful as the insulation on some wires (older) is thicker, so you must compare the metal only.
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Old 01-10-2011, 04:51 PM   #8
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Breaker Keeps Tripping


what brand of sub panel?
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Old 01-10-2011, 04:57 PM   #9
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what brand of sub panel?
Take a picture of the line feeding your main breaker and post it!
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Old 01-10-2011, 05:00 PM   #10
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Breaker Keeps Tripping


When I bought the place the subpanel had fuses, so about a year ago I had a friend who works for an electric company put in a new subpanel with breakers. So the subpanel is only a year old. I will check the brand of the subpanel later today. The main panel however looks very old. I will post pics too.
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Old 01-10-2011, 08:01 PM   #11
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Breaker Keeps Tripping


Main Panel



Meter

















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Old 01-10-2011, 08:34 PM   #12
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Breaker Keeps Tripping


I believe the subpanel is a cutler-hammer because that is the brand of breakers.





Subpanel breakers

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Old 01-10-2011, 08:53 PM   #13
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Breaker Keeps Tripping


Quote:
Originally Posted by Saturday Cowboy

More likely IMO is that there is a problem with the overhead wiring, from whipping in the wind. Check for damage, near points of support.
Thumbs up on this comment. Pic is rough but I would check the service entrances.
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Old 01-10-2011, 09:33 PM   #14
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Breaker Keeps Tripping


1. Well did anyone notice that the feed for the "shop" is landed on the buss lug and not a breaker.
2. It's not a 3 wire feed
3. How are all 3 breakers in sub panel on the same leg?
4. looks like the overhead wire could contact
5. no grounding in "shop"
6. why is it on its own meter?
7. Impossible to tell what size wire that is.
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Old 01-10-2011, 09:52 PM   #15
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Breaker Keeps Tripping


The wiring is old 2 wire romex with no ground.
Wiring is from the 50's.
It's on its own meter because it is a rental.
I don't know how all three breakers are on the one leg, I've haven't gone in the attic to look.
So there is now way to tell what size wire that is?

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