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Discussion Starter #1 (Edited)
I recently bought an older house (built in 1941). Most of the house is wired with BX cable. Some of the receptacles are reporting an "open ground" condition from a receptacle tester. I am in the process of replacing these with GFCI receptacles. One of the receptacles I replaced is tripping immediately upon turning a light switch on that is upstream of the receptacle. In the receptacle box, it appears there are two three-wire cables coming into and leaving the box. One wire from each cable are tied together, which I believe are either the hot or neutral wire going to the two light fixtures. I wired the two other wires from each cable to the line and load terminals on the gfci. The receptacles are both working properly when the light switch is off (the receptacle tester still comes back as "open ground").

My thought is that the light switch is sending power to the light fixtures that is returning through the receptacle somehow, which the gfci is reading as a ground fault. Is this thinking logical? Could it be possible that I have the hot and neutral wires reversed causing the gfci to trip? Is there something else I am missing?

The light fixtures worked when a standard receptacle was installed in this location, and it is just a standard switch, not a 3-way.

Thanks in advance for any help!
 

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Naildriver
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GFCI's don't trip on overload, but on a tiny difference in the hot and neutral. Check the switch boxes to make sure none of the neutrals are touching any of the grounds, or the sidewalls of the switch boxes.
 

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Discussion Starter #3
I will check that once I get home. What would the reason be for having a 3-wire cable entering and leaving the outlet box? The light fixtures and receptacles are on the same circuit. The wiring is BX cable, so my assumption is that it's original, meaning the switch and outlet have worked for years without problem before the GFCI.
 

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Naildriver
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IF the wires in the cable are not exposed (stripped and bcapped), no good reason. If they are capped, the electrician was using the box as a junction box.

I know they may have worked for 70 years, but often when wiring is disturbed, weird things happen. Check for the touching wires and let us know when you get home.
 

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My thought is that the light switch is sending power to the light fixtures that is returning through the receptacle somehow, which the gfci is reading as a ground fault. Is this thinking logical?

Yes. Simple solution is not to use the load side of the GFCI. If there are downstream receptacles, you'll have to replace them with GFCIs also.


(Are these cables really BX? If they are BX then the tester shouldn't read "open ground", assuming there's continuity between the cables and the box and the receptacle. In any case, GFCIs are a good idea since old BX isn't a great ground.)
 

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Discussion Starter #6
Yes. Simple solution is not to use the load side of the GFCI. If there are downstream receptacles, you'll have to replace them with GFCIs also.


(Are these cables really BX? If they are BX then the tester shouldn't read "open ground", assuming there's continuity between the cables and the box and the receptacle. In any case, GFCIs are a good idea since old BX isn't a good ground.)
I think that might be my best bet. There is one downstream receptacle that I also replaced with a GFCI, so the load terminals wouldn't be required. I was more so trying to do it as to keep track if I ever had to look into the box again.

I'm pretty sure they are BX cables. There are more receptacles upstream on the same circuit that show they are grounded, but at some point the ground connection drops out and the final three receptacles show open ground. I replaced those three receptacles with GFCI receptacles. The light switch in question is located in between GFCI #1 and GFCI #2, and causing GFCI #2 to trip. The lights are physically located between GFCI #2 and GFCI #3, although I'm not confident how they are wired. GFCI #3 is the end of the circuit.
 

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Discussion Starter #7
IF the wires in the cable are not exposed (stripped and bcapped), no good reason. If they are capped, the electrician was using the box as a junction box.

I know they may have worked for 70 years, but often when wiring is disturbed, weird things happen. Check for the touching wires and let us know when you get home.
The one wire of each cable is connected together under electrical tape. I assume this continues on to the lights. I did not want to undo the electrical tape but you can see that they are connected. The other 4 wires (two from each cable) are connected to the receptacle.
 

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Naildriver
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Not using the LOAD terminals on the first-in-place GFCI, and using downstream GFCI's will cause nuisance trips, which seems to be what you have. You don't need a ground for GFCI's to operate properly. Remove the downline GFCI's and use the LOAD side of the original GFCI and install regular receptacles where the GFCI's were vacated. Let us know how that goes. Seems we get more information with every post.
 

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Discussion Starter #9
I used the LOAD terminals of the first in-line GFCI for the downstream wiring. I never said that I didn’t. I know for a properly grounded system, the LOAD side outlets are protected by the GFCI. I figured the extra GFCI receptacles wer
en’t a bad idea being that they were all reporting as open ground.
 

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It's not necessary or recommended to cascade GFCIs. Replace the first receptacle in the circuit (regardless of its "open ground" status) with a GFCI and use the load side to protect the entire rest of the circuit (including lights, although that isn't critical), no other GFCIs required.
 

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Discussion Starter #12
I attached a picture of the wiring in the outlet box in question.

Last night I attached all four of these wires to the LINE terminals on the GFCI. I didn't have a standard receptacle to install in its place being that the old one wasn't in great shape. If that is the best option, then I will buy standard receptacles and install one here.

Either way, can someone help explain to me what the wiring idea is here? I am struggling with determining the reason for the extra wire, but maybe I am missing something.
 

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