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mrc59 02-28-2009 03:13 PM

Outdoor GFI tripping, wires have voltage
I wired a detached greenhouse with one 120V and one 240V circuit, and all wires run though the same conduit. The conduit has one outlet mounted on the side of the house, with a GFI. The outlets inside the GH are protected by the house GFI. The outlets are for lights and a fan. The 240V line is for a heater. Wire size, box load, load/line lugs downstream from the GFI are all proper.

Recently, the GFI started tripping when reset. I disconnected the downstream lugs, and the GFI works properly. When I tried to test resistance with a digital (Fluke) multimeter, I find low AC voltage, around 2VAC between hot and ground, and hot and neutral. With the 240V breaker tripped, there is less voltage, perhaps 0.6VAC.

That weirded me out! I traced the voltage leak all the way back to the breaker. With one lead on the neutral bus, one lead on the breaker script, breaker tripped, I find between 0.6 and 2.3 VAC!

I know GFI's measure the difference in current, but I can't even begin to check resistance in the downstream circuit with the low voltage leak.

Is this a peril of a digital meter?

I can't remove the GFI, but I need power back for the fan!

Anyone have an idea where to begin?

Blue Jay 02-28-2009 03:44 PM

Sounds like the voltage is induced, you would need to disconnect all wires at the breaker box that are running close to these wires to get rid of it. (including the neutral and ground)

kok328 02-28-2009 09:32 PM

Is the 120V GFI that keeps tripping, in the main panel or did you run this from an existing circuit from the house?

mrc59 03-01-2009 05:03 AM

I figured the voltage was induced all right, and never noticed it before. The breaker box is full of dual breakers. Lots of circuits! This is a sub panel.

This is a dedicated circuit to the GH. From the panel to the GFI (outdoor) receptacle, then on to the GH interior.

I'm starting to suspect the GFI itself. It looks like there is a mess of spider/bug crud within. I don't have spare handy, but it's been out there for several years.

triple D 03-01-2009 06:29 PM

check this....
make sure that all the ground wires in the sub panel are on a dedicated ground bar. And that it is mounted to the breaker box directly. Then check to see that all the neutral wires are on the same neutral bar, and that bar is in no way connected to the grounds or the panel box. Then make sure this practice is carried through all of the wiring related to green house. If your gfi will hold, with the outgoing wires disconnected, work your way through the circuit, hooking up each thing in line till you find the one that upsets the gfi. And digital meters suck in these cases, (in my experience) Good luck....

mrc59 03-02-2009 02:59 AM

Thanks and thought so
Thanks! Will do. I still have the "vintage" Sears analogue multimeter :)

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