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I moved into a new house recently. One of the outlets was a 2-prong, ungrounded receptacle. I wanted to install a GFCI so I could plug in 3-prong devices.

The old receptacle had 2 hot, 2 neutral and no ground wire. I tested with a multimeter to identify the line and load pairs and wired them into the GFCI.

Once I energized the circuit, the GFCI would not reset. If I remove just the load wires, the GFCI will reset and function.

I'm trying to figure out what could be the source of the problem. The downstairs bathroom appears to be on the same circuit and also has a GFCI. I can reset that GFCI no problem.

It appears to be downstream of the newly installed GFCI. Could the two be interfering with each other?

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  • Why are you even connecting the load wires? Jan 10 at 0:35
  • Also, are your junction boxes made of metal? If so, get a $3 "comes in a box" spec grade receptacle from the store, and install it with screws and all, but connect absolutely nothing to ground. Plug a 3-light tester into it. Do you get 2 yellows (good ground)? You might be grounded after all, and if so, I have a theory of what went wrong. Jan 10 at 0:43

3 Answers 3

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Figure out what is being fed downstream (what's dead now that it's disconnected?)

Strong likelihood that there is a ground fault on the wires connected to the load terminals. When a GFCI trips in this situation (newly installed) that's the most reasonable thing to suspect and go looking for.

GFCI's do sometimes fail with age. Defective out of the box is much rarer. So start with the assumption that it's working correctly, and go look for what is setting it off.

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As Ecnerwal's answer stated, you need to troubleshoot the problem by checking every receptacle, light, etc. that is on the load side of the GFCI. In additional to faulty appliances, any ground/neutral problem (ground path used as neutral or ground and neutral connected together) will cause the GFCI to immediately trip or to never reset.

As far as interaction between GFCIs, I highly doubt that is the problem here. A GFCI is essentially a monitoring system, and it actually monitors a very basic thing - hot current vs. neutral current. That should have absolutely no effect on any other GFCI elsewhere in the circuit. That being said, you should not have chained GFCI in a circuit because a fault past the 2nd GFCI might trip the first, might trip the second or might trip both - totally unpredictably, which becomes a usage problem, and usage problems discourage proper use of GFCI and other safety systems.

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  • Thank you! I hadn't realized the bathroom was on the same circuit. The house is wired very strangely. The room I'm working in has 3 outlets, 2 of which are on one circuit and this third one on another.
    – Rucian
    Jan 9 at 17:06
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One more thing that can cause this is mixing of neutrals. If the downstream neutral is interconnected to the neutral from another circuit, the GFCI will probably trip. This is because a GFCI actually functions by comparing current flow between hot and neutral. If they are unbalanced, it is assumed that current is flowing to ground. In this case, some of the neutral current is flowing through the parallel neutral.

This is a situation which is difficult to detect without a GFCI. It is also dangerous as a neutral wire could be overloaded and cause a fire.

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  • That is a good thought. The wiring in this house seems very haphazard. There are even outdoor receptacles that are just standard residential duplexes--not WR orGFCI or covered.
    – Rucian
    Jan 10 at 19:15

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