Circuit breaker did not trip

A tenant of mine had an outlet start sparking after trying to plug a lamp into it. There is an air conditioner on the same circuit as well. The sparking was bad enough to melt the side of the outlet where the wire get screwed in. Shouldn't the circuit breaker have tripped? Do cicuit breakers go bad such that they do not trip when they need to?
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Circuit breakers do go bad and fail to trip on overloads, but it is unusual. More commonly they trip unnecessarily when they fail.
But, they will not trip on arcs unless there is also an overload. Arc fault circuit breakers were invented for precisely that reason; to protect against arcs that did not involve overloads. They outlet was probably damaged, and that is what caused the problem. The breaker is "probably" okay, but unless you want to test it, you might rest easier replacing the breaker. Hey, why not replace it with an arc fault breaker?!
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Could the arc have been caused by bad wire? The outlet was only one year old, but the wiring is very old. Someone suggested that the wire is too old and needs to be replaced. If it is charred, can it just be cut back and used again?
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Without seeing I can't really answer that, but it seems unlikely. Since the arc happened when you plugged the light in (right?) the problem had to either be the outlet or the connection between the outlet and the wire. A defective hot wire does not need anything plugged in to short, and a defective neutral should not short unless it is completely broken. Did the person who installed the outlet know what they were doing? If the outlet is a year old and not abused, a bad connection sounds like the culprit. Was the wire attached to a screw terminal or pushed through a hole in the back. The holes in the back are very prone to failure, at least on the $0.99 outlets. If there is no visible damage to the wire, and it is not overloaded, it should be safe; though some 70 year old wiring looks pretty dicey.
If you have enough wire to cut it back to a sound section, it ought to be okay, though again, I can't see the wire so it might be prudent to get someone to see it if you have any doubt.
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On 14 Sep 2004 08:59:15 -0700, snipped-for-privacy@yahoo.com (balboni) wrote:

The wire itself doesnt wear out. Eventually the insulation can get so brittle that it breaks off when the wire is flexed but that doesn't sound like what happened to you. I would guess that the outlet itself failed (don't get the .99 home depot outlets) or, more likely, you had a bad connection. Did you use the backstab connections on the outlet or the screw terminals? I would suggest that you always use the screw terminals and make sure the wire is very tight.
You can cut the wire back to the point that the insulation hasn't been affected and the wire hasn't discolored from heat. Hopefully there is enough wire in the box for that. If not then you are looking at a bigger repair.
Steve B.
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OP said it went when the tenant tried to plug something into it... My bet would be improperly installed plaster-ears shifted when the plugh got shoved in, and either cut something, or bridged two screw-contacts.
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This is Turtle.
They sure do !
Replace the I.T.E. breaker for just good measure to be safe.
TURTLE
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I would also add that replacing the breaker might be a good idea if it's very old. Older ones aren't as reliable as newer ones. They sometimes go bad slowly with age.
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This is Turtle.
The general ideal of breaker getting bad with age is it will start tripping too soon or just trip with a little amps applied to it. Most all breaker will fail in the tripped possision in most cases. Generally speaking breakers don't fail in the closed possion.
If your going to change a breaker for age , your only changing it before it starts to fail and start tripping too soon and not start failing in the close possion.
Now if it is a I.T.E. breaker, all the thoughts above don't apply here.
TURTLE
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You can not afford to test an molded case circuit breaker. Here in Phoenix I know of only one company that has MC CB testers. And they can not test every brand.
Call a pro and have the circuit checked out. If you can "weld" with the circuit there could be something wrong with the grounding for the circuit.
For the ~15 bucks replace the offending unit. When you replace it. Force all of the breakers off and on a couple of times. Sometimes they will "freeze" into an ON position.
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On 13 Sep 2004 20:36:38 -0700, snipped-for-privacy@yahoo.com (balboni) wrote:

The circuit breaker only trips if you have an excessive amount of current flowing through it. In this case the outlet failed internally but the only current flowing was to the other devices on the circuit so the breaker was not overloaded.
This is a problem and current code requires the use of arc fault breakers in bedrooms that would trip if this were to happen. I wouldn't be suprised to see the arc fault breakers become a code requirement for all convenience circuits in the next few years.
Steve B.
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