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Discussion Starter #1 (Edited)
I thought I was gold. Outdoor weatherproof in-use-covered with 20 amp GFCI and a single pole switch to let us easily turn off the motion detector dusk-to-dawn lights next to it for being outside to look at the stars.

But turning on the switch to have the motion lights be "on" trips the GFCI. Only when the motion lights are connected... All testing with a multimeter shows the proper 120V happening with the flip of the switch without the lights connected...

Yes, the switch and other non-switched continuing power (to two outlets indoors) are all hooked up to the Load of the GFCI. I've used a multimeter to test for continuity between everything (all combos of hot, neutral, ground of the light sensor, neutral and ground of the Load power coming from the GFCI...). No continuity between any of those where there shouldn't be.

It's an old Brinks 180-Degree motion activated... (item 7150, Brinks) and I wouldn't mind at all buying a new one that might actually fit better with the 2-gang added box on the other side of the stud from the light, but I'm worried there is something inherently problematic with photocell stuff and a GFCI.

Any advice?
 

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Discussion Starter #3
Either the motion sensor or the light sockets are ground faulted.
The GFCI trips even with the motion lights not connected to ground at all. Live black from box to only motion lights black, and white neutral from box to only motion lights white... Does that rule out either the sensor or the light sockets being ground faulted? Thx...
 

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GFCI's don't trip on overload, but on a small amount of imbalance in the hot and neutral. It does not require a grounding conductor. So it appears you have a ground fault either in the sensor or in the fixture.
 

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Discussion Starter #5
I am suspecting the switch itself, and stupidly I did not try hooking the light up to the non-switched load. In other words tapping the same ground/hot/neutral wires that head down to the other two indoor outlets. I always used the switch's hot... Tomorrow!!

Thanks, and shall report back. If not using the switch still trips the GFCI, then it must still be something in the sensor lights/sockets... All did test "no continuity" via my multimeter, though...
 

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I've used a multimeter to test for continuity between everything (all combos of hot, neutral, ground of the light sensor, neutral and ground of the Load power coming from the GFCI...). No continuity between any of those where there shouldn't be.

You're not going to detect what could be a 5ma leak with a continuity tester. Somehow current going out is not coming back - you say it happens when you flip the switch so that rules out anything on the circuit that isn't switched.
 

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Discussion Starter #7
You're not going to detect what could be a 5ma leak with a continuity tester. Somehow current going out is not coming back - you say it happens when you flip the switch so that rules out anything on the circuit that isn't switched.
Right. The couple of outlets on the circuit but after the GFCI are not tripping the GFCI, so if I hook up the lights to that load that doesn't need the switch, and the GFCI then does trip, then I will figure the problem to be in the sensor motion lights unit. If the lights don't trip anything, then the problem is in my switch somehow. I will post what I recall my wiring to be...
 

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Discussion Starter #8
I think this is how I have all this wired. I started with an image I'd found for how to wire such an arrangement, but doctored it to show what I think I ultimately have. The GFCI outlet actually has Line on top and Load on the bottom, but this wiring reflects what I have in terms of Line and Load. The Light Bulb top right in the diagram, of course, would be the motion sensor lights. Flipping the switch on trips the GFCI regardless of whether the ground (green) is connected to the lights or not.

I guess the one ??? move I made here (not that there aren't other iffy moves) is that since I was using the box for the sensor lights also as a junction box to connect to existing old ungrounded Romex coming from "Load," I utilized the neutral wire from that and via the switch the hot wire is coming from "source" that is connected to the "Line" of the GFCI outlet.

Red flags that any real electricians or better DIY folks see that I'm missing?

Again, I plan on testing again tomorrow with the lights connected directly to the "Load" circuit (hot, neutral and ground) to see if that trips the GFCI, which may mean the old sensor lights have issues. Before the GFCI was there the lights never tripped the 20 amp breaker at the panel, but I guess GFCIs trip easier? Perhaps panel breakers do only trip on overload?

Thx
 

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If you have that wired up as you have shown in your diagram the GFCI should trip as soon as you connect the (PIR) light via the switch.

You have the black Line wire "feeding" the light (connected via the switch to the light) BUT the neutral is returning to the "Load" connection of the GFCI.

As soon as you turn on the light, the GFCI will detect the current returning on the Neutral but with no equal current passing to the Line side of the "Load" terminals.

If you want the light connected via the "Load" side of the GFCI, move the black Line wire feeding the switch to the Line (hot) connection of the "Load" side of the GFCI.
 

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Discussion Starter #10
Thank you, FrodoOne. That makes Baggins and Baggins of sense and does confirm the sad reality (due to the horror show of getting to and working with the innards of the two-gang box with the GFCI and switch for any chance to have the lights use the switch) of what the fix is... (either fix, powering the light via the switch from just source/line and have it not be after the GFCI, or doing it all via the Load by moving the hot to the switch over to Load to match from where my neutral is coming as you suggested)

In our early teens my friends and I all assumed our Hobbit/LOTR identities (based on only the books, of course, as I am not young), and I was Bilbo. Sure wish I could turn invisible now!
 
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