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Old 11-06-2015, 07:33 PM   #1
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Help with lighting Short


I think I have a short in my driveway lights. There are four 100 watt lights attached to a regular 120/240V breaker in our main breaker box. The four lights are the only thing attached to this breaker. They are hard wired with waterproof buried romex stuff. They worked just fine for about 8 years and all of a sudden they trip the breaker. I pulled off all the lamps from the poles and checked all the connected they all looked really good, some of the grounds were corroded but I cut them and put new nuts on. When I turn the breaker on sometimes some of the lights come on for not more than 30 seconds, I can hear a humming building up and then the breaker flips. Seems like there is a short somewhere but I can't get any of my electrician friends to come look at it. The fixtures themselves don't seem very water tight, I'm thinking either the breaker is bad or the fixtures themselves have a hidden short?!? The connections coming to the fixtures underneath in the poles look really good and I can't imagine a short appeared underground... Should I just get new fixtures?

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Old 11-06-2015, 07:43 PM   #2
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Turn off the breaker.
Remove all the lamps
from the fittings.
Carefully measure
the resistance across
the hot line to the lights
And the neutral of the same line.
With no lamps there should
No resistance. If there is ?
Then you have a short.
Certainly possable
With underground wiring.
Cause water will get in.

Be careful in the panel:
Take all precautions.

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Old 11-06-2015, 09:33 PM   #3
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Some of the lights come on? I would turn off the breaker and remove the cable leaving the last light that comes on. Remove the bulbs and measure the resistance of the cable you disconnected. If it measure shorted then you just need to find the problem spot.
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Old 11-07-2015, 06:09 AM   #4
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Quote:
Originally Posted by dmxtothemax View Post
...With no lamps there should
No resistance. If there is ?
Then you have a short.
Certainly possable
With underground wiring. ...
A wiring short is signified by "no" resistance (practically speaking less than five ohms) with nothing plugged in or turned on.

With no lamps there should be "infinite" resistance between hot and neutral and between hot and ground, practically speaking, more than 100,000 ohms.

There could be intermediate amounts of resistance. If so you should be suspicious because that will result in current leakage in a manner similar to a short circuit which is likely to worsen over time.

Always turn off power before doing ohms or resistance measurements.
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Last edited by AllanJ; 11-07-2015 at 06:19 AM.
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Old 11-07-2015, 02:48 PM   #5
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Quote:
Originally Posted by dmxtothemax View Post
Turn off the breaker.
Remove all the lamps
from the fittings.
Carefully measure
the resistance across
the hot line to the lights
And the neutral of the same line.
With no lamps there should
No resistance. If there is ?
Then you have a short.
No, there should be infinite resistance. With a short there would be no resistance, or close to it.
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