GFCI not playing nice with lightpost

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  #1  
Old 05-23-19, 04:05 PM
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GFCI not playing nice with lightpost

In the past few weeks I've replaced some conduit and wiring in the garage, and added a GFCI that trips every time a load larger than a light bulb is put on any of the downstream outlets (and GFCI outlet itself). After extensive troubleshooting I have narrowed the issue down to the light post outside the garage, which is at the very end of the circuit. The underground cable from the garage to the post has not been replaced, nor has the timer which controls the light post.

When the wiring is connected at the light post (2 red wire nuts in the picture), the GFCI will NOT trip if the light post timer is actuated or the garage door light is on, but any load greater than this trips the GFCI, no matter which outlet the load comes from. The only time that the GFCI does not trip under heavy load is if the neutral at the light post (red wire nut) is disconnected, regardless if the light post is on or off. To test this theory, I disconnected the wiring at the light post (two red wire nuts) and turned on a leaf blower in the garage. As soon as I touch the neutral wires together (previously under the red wire nut), the GFCI trips.

I proceeded to replace the wiring inside of the light post lamp that travels from the red wire nuts to the bulb holder itself. This did not improve the situation. There is nowhere inside the light post to attach a ground wire. Replacing the GFCI itself had no effect. I don't know how to proceed from here, any help would be appreciated.

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Last edited by DIYNovice; 05-23-19 at 05:40 PM. Reason: resized pictures
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Old 05-23-19, 05:11 PM
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In the picture with the light bulb...... the shell of the lamp socket is neutral/white and the center pin should be hot/black. However..... neither of those connection should be touching any ground.

On a GFI circuit..... all neutrals must pass thru the GFI along with the hot wires.
It sounds like you have a short/leak from neutral to ground. It could be right at that light socket.
Hard to see what type of socket it is.
 
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Old 05-23-19, 05:33 PM
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Thanks...upon further inspection of my notes of the original garage wiring installation, I realized that the garage/light post was NOT on the GFCI, probably because of this issue. Is there any way to correct this problem without replacing the light socket? It is a harp light that is an old family heirloom...probably 1940's or earlier
 
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Old 05-23-19, 06:42 PM
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It looks like the light socket in the lamp might have a mogul base (a larger size) and there is a reducing adapter screwed in to allow standard size bulbs. It's hard to tell for sure in the picture, but if it has the adapter unscrew it. If it looks marginal then replace it.
As Pete said it sounds like there is leakage from the outside shell of the socket to the lamp housing. It appears that you might be able to disassemble the socket and clean off the ceramic insulating parts, especially if it's all screwed together.

 
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Old 05-23-19, 07:04 PM
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If the light socket touches ground..... there is no way to make it safe.
You said the light is currently not connected. Are you sure neither wire is connected ?
Just the neutral touching can cause a problem. GFI trip)
 
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Old 05-24-19, 05:19 AM
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I would bet you can find a modern bulb socket that can be adapted to fit in the historical housing. Most hardware and big box stores have a section of light fixture and lamp repair parts with various different types of bulb sockets. There are online stores with tons of lamp and light fixture parts both modern and historical.
 
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Old 05-24-19, 11:55 AM
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I had never noticed that there was a mogul bulb adapter in there, and that turned out to be the key piece of information to solving my problem. The light started its life as a city street light and was bought at a surplus sale in the 70's. I took the lamp apparatus out this morning and discovered (under 40+ years of bug crud) that there was a copper strap bonding the neutral to the light frame. I suppose this was necessary when used as a street light. I removed this strap and presto the GFCI now works perfectly with the old harp light. Thanks again for all the help!
 

Last edited by DIYNovice; 05-24-19 at 12:12 PM.
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