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Old 09-15-2008, 10:46 AM   #1
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Testing circuit with GFCI protection


I replaced a GFCI over the weekend, and I found something that I don't quite understand. I have two of those little testing gizmos that plug into a 3-prong receptacle (the kind with one red and two amber indicator bulbs), and I know they are both working because I plugged them into a known working outlet and got two amber lights (normal indication).

What confuses me is that when I plug them into an outlet on circuit protected by the GFCI, they don't light up at all even though the circuit is hot. Is there something about the GFCI protection that renders the testing device inoperative? If so, is there a safe way to test for hot circuits before I start poking around inside the boxes?

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Old 09-15-2008, 10:53 AM   #2
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Testing circuit with GFCI protection


You might double check one thing. When one of my testers doesn't light up at all, it actually indicates some sort of incorrect wiring (but I can't remember what it is indicative of), even when there is power to the receptacle. Check the legend on your tester to see if no lights means something like an open neutral or phase and neutral reversed, for instance.

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Old 09-15-2008, 10:55 AM   #3
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Testing circuit with GFCI protection


The testers you describe should work on any receptacle. Are you sure you reset the GFCI before inserting the tester?
I also know that some types of testers will actually trip the GFCI. See if that is the case.
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Old 09-15-2008, 11:27 AM   #4
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Testing circuit with GFCI protection


You are correct that I suffered an extreme brain cramp on this one. The GFCI works perfectly, but when I tested it I had failed to throw the switch that energizes the circuit. Duh!!!

I actually have two problems. One is that the GFCI was tripping when I turned on the underwater swimming pool lights. The hot link comes from a master control panel that handles the programming for the filter pumps, heater, etc. and when I energized the circuit it would pop. That branch of the circuit feeds three wires that then disappear into three separate pieces of conduit that immediately go into the concrete. When I disconnected the first one, the lights work and the GFCI does not trip. My only problem is that I can't for the life of me figure out what the heck that wire is connected to! There are two pool lights and they both work (I suspect they each have their own conduit) but since the branch is only powered when the "pool light" button is activated, I will be darned if I can tell what the other wire is for! At this point, I just disconnected it and put some wire nuts on the bare wire.

The other problem was a outdoor receptable in a water resistant box. I thought maybe that it was on the same circuit (wrong) but the tester did not light up. As you suggested, I looked more carefully at the test patterns and no lights means "open hot". When I was checking this receptable, I tried both the tester and I probed with with my volt-meter and got no indication of voltage. However, when I started to remove the receptacle to look at it more closely, something arced and I got the classic "pop" sound from inside the box. I suspect the outlet is back wired instead of side wired, and there is a bad connection there.

Since the tester and the volt-meter both do not register, before I replace this thing do you have any advice on how to make sure I have the right breaker turned off at the panel, or do I just do the ultra safe thing and kill all the power at the main panel? I am wondering if probing with one of those non-contact tester will show the circuit status if I have a hot open.
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Old 09-15-2008, 11:43 PM   #5
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Testing circuit with GFCI protection


Quote:
Originally Posted by Hodag View Post
Since the tester and the volt-meter both do not register, before I replace this thing do you have any advice on how to make sure I have the right breaker turned off at the panel, or do I just do the ultra safe thing and kill all the power at the main panel? I am wondering if probing with one of those non-contact tester will show the circuit status if I have a hot open.
My suggestion would be to shut off the main, pull the receptacle out and disconnect it, temporarily cap the wires, look for damage to the wire insulation. If the wires are ok and all looks well, turn the main back on and test for proper voltage & polarity at the wire ends. If all's good, next step is to find the breaker it is on so you can label the panel. After that, re-install the recpt (I rarely back-stab a recpt), turn the brkr back on and do one last test. Should be good to go.
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