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Electrical mystery

Sifu

SAWHORSE
Joined
Sep 3, 2011
Messages
2,800
This is an issue I encountered in my own house two nights ago.

I noticed the overhead lights in my dining room, foyer and front porch were not working. No tripped OCD. In trying to get some light to see inside the switch boxes, I noticed the dining room outlets were also not working, no current was detected with my standard pen sized meter, however there was evidently enough to cause one of the indicator lights on a device I had plugged in to flash. No OCD tripped obviously. The receptacles and lights are on different circuits. I shut them off until the light of day. Once I could see, I found a damaged 3-way and broken hot, which I fixed and the light mystery was solved. When I checked the receptacles, they now work...all by themselves. Many years ago in another house I encountered an exterior GFCI that also intermittently worked without tripping and what I think was the cause. I attributed it to the expansion and contraction of the copper conductors during large temperature extremes, causing the conductor to become loose at a terminal and making intermittent contact with a terminal. I tightened them and never had another issue. Does this sound plausible? I am guessing the same here and now but have yet to track down a loose conductor. I also suppose a conductor could become loose in the panel, which is in the garage where the most extremes in temperature occur, but I haven't had time to check that. We have had some recent 40 degree temperature swings overnight. Ground faults and short circuits don't seem to be the cause because no OCD ever tripped. I do find it odd that these events occurred at the same time, but I suppose the same temperature swing could have caused enough stress on these conductors and devices at the same time to create both issues. Or just total coincidence.
 
I think what you describe is totally plausible. You may consider one more investigative step that wouldn't take too much time. Turn off the breaker, open the first switch and disconnect the ungrounded conductor (hot) that brings power to the light circuit. Cap that conductor and turn the breaker back on, then test the outlets again. Assuming the outlets still work than you're probably on the right track. If they do not then the problem could be a little more complicated...
 
there is a meter called a Shur-Test (spelling?) that simulates a load and not just read voltage.
So the high resistance situation you describe with the probable loose connection would show up if you used that meter. It is a little pricey but worth the money when a connection like that could heat up and potentially cause a fire
 
I think what you describe is totally plausible. You may consider one more investigative step that wouldn't take too much time. Turn off the breaker, open the first switch and disconnect the ungrounded conductor (hot) that brings power to the light circuit. Cap that conductor and turn the breaker back on, then test the outlets again. Assuming the outlets still work than you're probably on the right track. If they do not then the problem could be a little more complicated...
First thing I did. Outlets all worked.
 
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