GFCI Master Not Tripping

Mark Twenhafel

So we're doing a trim out today and new guy (me) is checking the exterior GFCI receptacles to make sure they trip. I'm using a plug tester with the pushbutton. The problem that we got stuck on was a master GFCI receptacle that didn't trip when tested. Of course, all the slaves on the load side behind it wouldn't trip, either.

So, I pulled it out and disconnected it's line and load cables and then tested each cable separately to check that (1) it was properly wired, and (2) it wasn't double-fed. Checked out fine: 120V on the line side and 0V on the load side. I noticed, however, that it would trip when only the line side was terminated (i.e., no load receptacles connected). Reconnected the load side and, again, no trip when tested.

Maybe it's a bad GFCI master. So I swap in a new-from-box GFCI master. Still won't trip. Maybe it's a bad batch.

What I do next is take a known-good GFCI master from the garage and swap it into the exterior location that's causing the problem. Once it's in, the known-good device stops working and acts like all the rest.

At this point, my lead with 5 years experience is stuck. So, I call the owner, a union-trained electrician with 26 or so years of experience. She says "that's strange," but has no ideas.

Anyone here have any ideas?

Canuck Sparky

Could it be that your tester is NFG?

thom

Canuk might have it.

A few years back my tester tripped a gfi, the inspectors didn't. His tripped the rest in the house, but one wouldn't trip. I had to replace the receptacle and everything was fine.

randomkiller

Instead of using the plug type tester just use a wiggy and put one probe in the hot side of the outlet and touch the other probe to ground, it should trip right out.

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goose134

Random is right, this is how I found out a commercial kitchen GFI wasn't tripping.

Mark Twenhafel

Tester bad?: I wondered about that, too. The tester properly tripped other GFCI masters on other circuits before and after it didn't trip the suspect outlet. In fact, the same tester properly tripped the "known-good" master in the garage before I moved that GFCI master to the exterior, where it wouldn't trip. Will try shorting the protected outlet to ground.

My thought: I'm thinking of testing continuity on each side of the GFCI, from the panelboard to the master and then from the master to the first slave.

This was the last house on which a guy they had to let go helped on, and were finding bad make-up in various places.

Magnettica

The problem is on your load side because when the load is attached, the GFI trips. Isolate the known load side of the circuit and go one-by-one until you find the culprit. My guess would be one of the subs on the job has a faulty power tool.

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220/221

I test GFCI with a wiggy to ground also. If the receps on the load side didn't trip I would suspect reverse polarity.....but a neutral to ground short should trip it too so......I'd pull everthing apart and looksee. It's only a few outlets, shouldn't take too long.

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Just because it's within code doesn't make it safe.

Just because it's against code doesn't make it unsafe.

JohnJ0906

Will the GFCI trip with the test button? If it does, will the downstream receps lose power?

The plug-in tester requires a EGC to operate, as does the wiggy method randomkiller posted. Have you checked that?

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All replies based on the 2008 NEC

Mark Twenhafel

...

220/221

If you lost your ground after the GFCI outlet the tester might not work.

I don't really know how the tester is designed. I know how a wiggy works though

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Just because it's within code doesn't make it safe.

Just because it's against code doesn't make it unsafe.

Magnettica

I don't know if this is appropriate or not but, normally I use the term line/ load when working GFCI circuits.

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JohnJ0906

It just shunts from the "hot" to the EGC (through a resistor). No EGC, it will not trip the GFCI.

The test button on the GFCI shunts from load hot to line neutral. EGC not necessary for the test.

Mark, are the load side receptacles working properly, and just not tripping?
Does the test button on the GFCI work?
Is the EGC good?

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"One Day at a Time"
All replies based on the 2008 NEC

JohnJ0906

These are the proper terms.

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All replies based on the 2008 NEC

Mark Twenhafel

Thanks for the info on how the tester works vs. how the GFCI works.

It's the load side that's not working. Disconnect the load, and then the GFCI trips. Take the tester down the circuit to the subs, and the subs test okay, i.e., two yellow lights, but they won't trip when the button is pushed.

We didn't go there today. Maybe Wednesday. Thanks for all the suggestions.

Magnettica

And that's really the best way to learn. There's so many nicknames for things in our industry that it can create some unnecessary confusion. For instance today, me and another had to replace a T87 thermostat. He kept calling the heat anticipator the "differential device".

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Mark Twenhafel

It took a while for us to get back there, and I didn't get to go. What I heard, in some detail, is that somehow the circuit feeding the GFCI master in the garage got interconnected with the circuit feeding the GFCI master on the exterior. Co-worker said that it took them a while to figure it out and that even then they didn't entirely understand the cause, but everything worked when they left.

What they learned from testing is that shorting one particular exterior recep tripped the garage master, and after the garage master tripped, everything else worked properly.

From this, I came to the conclusion that something was double-fed, interconnecting the two GFCI circuits. Not sure what they changed, but the guy telling me worked with a bunch of pot-heads for a while, so he got pretty good at troubleshooting. :-)

Thanks for all the suggestions.

Mark

JohnJ0906

That's how I learned...

Thanks for letting us know what the problem was... or at least that it is fixed.

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John from Baltimore
"One Day at a Time"
All replies based on the 2008 NEC