# GFCI Won't work with photocell



## Oso954 (Jun 23, 2012)

Why do you think the exterior light would require GFCI protection ?
Is it in a pool area ?

If there is no requirement, I would put it on the line side.


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## BrokerDon (Apr 6, 2015)

The light is in a flower bed, and I was not the original installer so I don't know how deep the cable is. It's a real possibility the the cable could get accidentally hacked by a steel tool cable someday.

But regardless... the question isn't about requirements, it's about why a photocell can't work on the load side of a GFCI outlet. Any idea?

--DOn


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## mpoulton (Jul 23, 2009)

There is no reason it wouldn't work. The ONLY way a modern GFCI trips is if there is an imbalance between current flowing out on the hot line versus current flowing back on the neutral. Somewhere between the GFCI and the light bulb, you have a "leak". Are you sure there isn't an inadvertent connection from neutral to ground somewhere around the photocell?


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## Pharon (Apr 14, 2014)

If the light works fine with the GFCI, then your problem is the photocell. Did you check it for cracks/leaks? If the inside is getting wet, that could be causing your nuisance trips.


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## BrokerDon (Apr 6, 2015)

I thought so too, so I simply replaced the first one. The second one appears to be in perfect condition right out of the box, but still exhibits the same symptons. (it's in a dry location.

The light that the photo-cell is controlling is an LED floodlight. I could see how sometimes an LED bulb can confound a photocell sometimes, but the GFCI tripping is the part that doesn't make sense.

--Don

--Don


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## ddawg16 (Aug 15, 2011)

Are you sure you have the GFCI wired correctly? 

A common mistake is to tie the two neutrals together.

And....does your photo cell use a ground wire? Some photo cells and occupancy sensors depend on the earth neutral for the device to work.

Can you post up a sketch of how you wired it?


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## Pharon (Apr 14, 2014)

ddawg16 said:


> And....does your photo cell use a ground wire? Some photo cells and occupancy sensors depend on the earth neutral for the device to work.


This is an excellent point. If the neutral and ground are connected at the photocell, you will have some neutral current from the LED light flowing back on your equipment ground, which will cause an imbalance in your hot and neutral wires.

I bet that's the culprit.


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## BrokerDon (Apr 6, 2015)

I guess I can never say I'm really sure of anything 

Let me try a quick text reply first, I can send a sketch later when I have more time if needed. I think you may be on to something with the neutrals.

The photocell does not have a ground connection.

The GFCI outlet has hot and neutral connections to the "line" terminals. (coming from my main panel),

On the "load" side of the GFCI, I have the photocell+garden light, and also another outlet, and a motion light. The "hot" (black wires) of the photocell, the second outlet, and the motion light are pig-tailed together and connected to the hot, load-side of the GFCI, and the neutrals (white wires) of those 3 devices are likewise pig-tailed together and connected to the neutral, load side of the GFCI.

In other words, EVERYTHING down-line of the GFCI outlet is connected to the load side of the GFCI outlet together.

--Don


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## Trackin_it (Apr 6, 2015)

Someone told me on another board that photo-sensors sometimes don't play well with GFCIs, but that's only "third-hand info." I've never noticed problems with any (small wattage) photo-sensing lights in GFI outlets.

Since at least one manufacturer builds photo-sensors and LED "guide lights" into GFCI outlets for certain applications, there could be something else going on with yours besides the sensor.

That's not much help, I know, but call it a "free bump-to-top." :wink:


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## BrokerDon (Apr 6, 2015)

mpoulton said:


> GFCI trips is if there is an imbalance between current flowing out on the hot line versus current flowing back on the neutral.


If there is such an imbalance, then it only occurs when the photocell is in the circuit. When I by-pass the photocell, everything works and the GFCI does not trip.

--Don


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## Pharon (Apr 14, 2014)

BrokerDon said:


> The photocell does not have a ground connection.


So the photocell has only 2 black/white wires on the line side and only 2 black/white wires on the load side? No other colors? And no equipment ground wires anywhere in the circuit at all?


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## BrokerDon (Apr 6, 2015)

It has 3 wires: incoming line (black) neutral (white) and outgoing switched power (red).

--Don


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## Pharon (Apr 14, 2014)

Is it wired like this?


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## BrokerDon (Apr 6, 2015)

Yes.

I've made a drawing of the entire arrangement, attached.

--Don


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## mpoulton (Jul 23, 2009)

There simply MUST be a ground fault or neutral-ground connection somewhere in there. Try disconnecting the load-side wires from the GFCI and checking resistance between each of them and ground.


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## ddawg16 (Aug 15, 2011)

mpoulton said:


> There simply MUST be a ground fault or neutral-ground connection somewhere in there. Try disconnecting the load-side wires from the GFCI and checking resistance between each of them and ground.


^^I concur as well

Your photo cell could be picking up a ground through the box just from physical contact.


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## BrokerDon (Apr 6, 2015)

mpoulton said:


> There simply MUST be a ground fault or neutral-ground connection somewhere in there. Try disconnecting the load-side wires from the GFCI and checking resistance between each of them and ground.


Did this.

There is a neutral-ground connection EVERYWHERE. Is this not right? In other words, I have full continuity (no resistance) between my white (neutral) wires and my ground wire. I checked several other outlets around my house and found full continuity between the neutral side and ground in each of them as well.

Regarding the comment about the photo switch picking up a ground connection through the box: I can't see how. The housing and the threaded shaft that protrudes through the electrical box cover are completely plastic.

--Don


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## mpoulton (Jul 23, 2009)

BrokerDon said:


> Did this.
> 
> There is a neutral-ground connection EVERYWHERE. Is this not right? In other words, I have full continuity (no resistance) between my white (neutral) wires and my ground wire. I checked several other outlets around my house and found full continuity between the neutral side and ground in each of them as well.
> 
> ...


Did you disconnect the wires from the load side of the GFCI first? Neutral and ground are supposed to be connected to each other only at one single location, in the main panel or before it. You should read continuity from neutral to ground only when the neutral wire is connected back to the main panel.


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## BrokerDon (Apr 6, 2015)

Makes perfect sense.

Yes I did disconnect them, and yes, I did have continuity between neutral and ground. Thanks to your clarification, I can see that the continuity I found between neutral and ground in my other outlets SHOULD be there, but that it should not exist in my disconnected light wires.

I guess my conclusion will be that I have a partially cut, or mole-eaten neutral wire underground somewhere since everything looks good on both ends that I have access to. Crap.

--Don


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## Pharon (Apr 14, 2014)

I thought you said the GFCI doesn't trip if you take the photocell out and just connect everything else? Because if that's the case, then it means there's something internal to the photocell causing the problem -- and not a neutral-to-ground connection somewhere else downstream of the service.


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## BrokerDon (Apr 6, 2015)

You are correct. Maybe I'm too anxious to nail down a solution. The two photocells are both the same make, and came from Lowe's. I'll try a different brand and see if the problem persists.

I've been resisting this, because it's quite a chore: I will also remove the light fixture and isolate the underground cable for a thorough test, just to put the question of a "ground leak" to rest.

Thank you, everyone, for the discussion. Hashing things out on this forum helps keep the brain working when it comes to trouble-shooting.

--Don


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## Trackin_it (Apr 6, 2015)

Your drawing in post #15 was pretty good. :thumbsup:

How much would you charge to make one of the circuits in my place, so I can map the dang short or whatever it is that I need to track down and correct? (I'm only half-kidding about having you draw one for me. I did manage to sketch something with Microsoft Paint, but it's not as good as the one you drew for the Case of the Phlummoxing Photocell.) :icon_cheesygrin: 

Good luck with fixing the photocell situation. I hope there's not too much digging or other labor involved in making that right.


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## BrokerDon (Apr 6, 2015)

Ha! its funny you mention that, I searched all over for an Android app I could use to make a diagram on my phone, but it's just impossible. Anything that's actually designed for electrical circuits is way too complex for simple stuff. I ended up using Microsoft Publisher on my desktop machine to make the drawing with simple shapes and lines and then exported it to a jpg file.

--Don


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## Pharon (Apr 14, 2014)

Nothing beats AutoCAD for this kind of stuff. Here's part of my 1st floor that I put together:


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## Trackin_it (Apr 6, 2015)

Wow. I had M$ Pub98 ages ago, and did some good stuff with that, but you guys have me beat. AutoCAD is like _Star Trek_ stuff to me. <"bowing down" smiley goes here>

I'll probably just use the crude GIF I made last night to log the ohmmeter readings as I go around trying to pinpoint the apparent short we have somewhere on one particular circuit.
At least I'm learning lots of new things lately. I consider a day wasted unless I learn something new (preferably without breaking anything during the learning process), but this new 'lectrical stuff is Right Out There.


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