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I recently ran power to a small shed in my backyard. I extended a 15amp circuit that was powering only a gate motor. The #12 wire enters the shed and transitions to 14/2 Romex at a disconnect. The circuit is very simple: it feeds a GFCI receptacle (first image) then passes to a single pole light switch (second image) that switches hot wire to a standard receptacle with a fluorescent shop light plugged in (third image).

Everything is wired properly and works fine, except the fluorescent shop light plugged into the standard receptacle at the end of the circuit causes the GFCI to trip when turned off (most of the time). I have tried plugging the light directly to the GFCI with no problems. I have tried replacing the shop light with a small 60 watt light with no problem. I have tried replacing the shop light with a small air compressor with no problem. It seems to be this shop light causing it to trip when plugged into an outlet downstream of the GFCI. I'm at a loss on what to try. Could it be a bad GFCI? Why is it only this scenario causing it to trip?

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    You did split the neutral on the GFCI.... right?? line and load? – JACK Sep 10 '20 at 19:01
  • Excuse my ignorance: What do you mean by "split the neutral"? – Inquisitor Sep 10 '20 at 19:13
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    There is a separate connection for the line side and the load side of a GFCI outlet. You have your hot and neutral from your panel going into the line terminals on the GFCI outlet. Then you have your hot and neutral going from the load terminals of the GFCI to your switch. They have to be separated from the line. Your neutral is split through the GFCI. – JACK Sep 10 '20 at 19:29
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    As a side note: you extended 12 gauge wire with 14. Are you sure this is on a 15 amp breaker? If the breaker is 20 amps, the 12 gauge wire would be legal but the 14 would not. – DoxyLover Sep 10 '20 at 20:34
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    I used #12 for the 80' run to reduce voltage loss. It's definitely a 15amp breaker. The wire to the gate motor that i tapped off of is 14 gauge. – Inquisitor Sep 10 '20 at 20:52
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Well, this is embarrassing, but hopefully it helps others in the same situation. I used an old 3-way switch I had lying around and I mistakenly connected the ground wire to the other switch terminal rather than the ground terminal. So when I switched it to the off position current was leaking to ground and tripping the GFCI.

I wired it correctly and it's all working as it should.

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    Thank you for posting this follow-up. - Too many OPs dump us as soon as they get what they want. They don't write, they don't call, we never even find out if they made their homes warm and bright or if they got electrocuted. – A. I. Breveleri Sep 12 '20 at 22:54

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