Changing Out a GFCI Receptacle

Little Bill

Little Bill

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Tennessee NEC:2017
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Semi-Retired Electrician
I went to change out a GFCI receptacle today and had a strange experience. After putting in the new receptacle, it wouldn't set. I took care in making sure which conductors were line & load. I thought maybe the bare ground is touching the neutral so I checked that first. It was clear of the neutral so I thought maybe I got line & load reversed. To verify that I took the conductors off and turned the breaker back on. I was using a non-contact tester to find the hot. But I sounded off on both sets of conductors. So I got my meter and a test lamp to rule out a false reading. Turns out both sets of conductors were hot!

The receptacle had been double fed off the same circuit. The customer said he had noticed that part of the receptacle wasn't working and figured the GFCI was tripped. He said the reset button wouldn't work so he called me. I didn't check anything other than if the receptacle would reset, which it didn't. So knowing they fail, I just replaced it. He told me that part of it would work but the other part would not. It makes sense now that I know it was double fed. Apparently the side with the other feed was on the load side and it would work because it was live from the other feed.

This had to be an old GFCI because they used to fail closed. Meaning they would still work but the GFCI portion would not be protecting. New GFCIs have to fail open, which neither line or load will work.
I told the guy it was lucky the other feed was on the same circuit or he would have had 240V at the receptacle.
I just capped off the extra feed.
 
the old gfi outlets would back feed and energize the receptacles if you put power to the load side.
I'll bet it never tripped the breaker either.
 
Little Bill said:
New GFCIs have to fail open, which neither line or load will work.
Click to expand...
Key words are fail open.

I posted results fairly recently of some experimenting I did with the Legrand GFCI's, haven't tested any other brands to see if they do the same.

Bottom line was the unit won't reset if reverse wired. If you have it reset then swap line and load it will continue to pass power, but once it does trip it will not reset until wired properly again.

Your scenario of being fed from both ways is something I never thought of trying. Something tells me it may try to reset simply because of power on the line side, but at same time the injected test signal intended to detect neutral to ground faults likely would still cause it to trip immediately as you would have part of that test current passing outside the sense coil.
 
kwired said:
Key words are fail open.

I posted results fairly recently of some experimenting I did with the Legrand GFCI's, haven't tested any other brands to see if they do the same.

Bottom line was the unit won't reset if reverse wired. If you have it reset then swap line and load it will continue to pass power, but once it does trip it will not reset until wired properly again.

Your scenario of being fed from both ways is something I never thought of trying. Something tells me it may try to reset simply because of power on the line side, but at same time the injected test signal intended to detect neutral to ground faults likely would still cause it to trip immediately as you would have part of that test current passing outside the sense coil.
Click to expand...
The new GFCI would not set at all. As soon as you pressed the reset button it would just pop back out.
 
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