Breaker for garage tripping instantly

[tel0004]

My house was built in the 50s. I have a detached shed built in the mid 90's.

The shed has one 20 amp breaker that will trip instantly when I turn it on. It worked fine in December, but I have not been back there with the snow. Right now I have about 300 watts of lighting hooked up, but nothing else, so its not overloaded.

What if anything can I do do troubleshoot this?

The shed was built long before I bought the house so I dont know exactly where the line is burried.

 

[G_P]

Sounds like a short circuit. I would bet that the buried line is the culprit, if not that then check the wiring in the shed for places that have been chewed through by rodents.

To troubleshoot it, remove the wire from the breaker and the neutral bar, and check the ohms between the 2. If its is at or near zero there is a hot/neutral short. Do the same with the hot and ground wires to check for a hot/ground short.

 

[pattenp]

Could be a short due to bad wire insulation or the wrong type of wire under ground from moisture penetration. A multimeter may not show a problem because the test voltage in the meter is not high enough to produce current flow through wet wire insulation. The higher line voltage can arc between the two conductors if the insulation has gotten wet. If you isolate/disconnect the feeder in the shed and the feeder source breaker still instantly trips then the feeder definitely has a short.

 

[6768rogues]

I have replaced bad breakers that tripped constantly. That is rare, so I would check what the above posters said first.

 

[wyliesdiesels]

for GP and pattenp

 

[justsam]

My house was built in the 50s. I have a detached shed built in the mid 90's.

The shed has one 20 amp breaker that will trip instantly when I turn it on. It worked fine in December, but I have not been back there with the snow. Right now I have about 300 watts of lighting hooked up, but nothing else, so its not overloaded.

What if anything can I do do troubleshoot this?

The shed was built long before I bought the house so I dont know exactly where the line is burried.

Not sure how to interpret when you say "the shed has a 20 Amp breaker"
Is the breaker in the shed or in some other location feeding the shed?
Is the any type of breaker panel in the shed?

 

[wyliesdiesels]

OP do u have an update?