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I've been having some issues with what I thought were ghost GFCI trips in my shop. The shop is a metal building, all 20a 120v outlet circuits are routed through a GFCI outlet at the start of the circuit. Over the past year, I had one of the three GFCI circuits tripping intermittently, maybe a few times a month. It seemed when like over the summer it didn't really trip but it recently got colder and started tripping more frequently. I've tried removing all devices plugged into this circuit but it still trips.

Fast forward to yesterday, I installed another circuit again starting with the GFCI as the first outlet. I tested the circuit and GFCI, ran some power tools, etc. and everything seemed fine for a few hours. I turned off the lights in the shop and took a break. A few hours later I came back and all circuits were still working. As soon as I turned on the light switch (wired through a separate breaker), both my new GFCI and the one I previously had issues were tripped. I know that I have not crossed neutrals in any of the boxes since I know exactly where each wire runs.

The light circuit is on a separate breaker with no GFCI. The light circuit has several old fluorescent fixtures, probably 40 years old. 4-5 are 4 ft units, one 8 ft fluorescent unit. The rest are all newer LED units without ballasts. I've read that fluorescent lights can trip GFCI's, but my question is can they trip GFCI that are on separate circuits? I also know that the lights start a little slower depending on temperature.

Update 10/8/2020: This morning when I turned the lights on the first time, the GFCI's on both circuits were tripped. After the first time, I could not replicate the issue. Also some more information on brand if it matters. Both GFCI's that I'm having issues with are "Smart Electrician" brand. The other two GFCI's are different brands, one a Legrand, the other I can't tell without taking it out of the box.

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  • Well developed question + Is the panel in the shop a main panel or sub-panel? If a sub-panel, are you sure the ground and neutral are properly separated and that there are ground rods properly connected to the grounding buss bar? Oct 8 '20 at 14:33
  • On the outside of he building is a 400 amp meter that splits 200a to the metal building, 200a to the house. There's a 200 amp panel inside the building that feeds the original GFCI which has been giving me issues for months. The two GFCI circuits not giving me any problems are also connected to the 200 amp main panel. There's a 100 amp sub panel on the other side of the metal building that the new GFCI is connected. The sub panel has separate neutral and ground wire running to the main neutral and and ground bars.
    – ed729
    Oct 8 '20 at 18:14
  • Yesterday when I had issues it was around 60F temperature and the lights had been off for several hours. I could trip the GFCI multiple times just by flipping the light switch. This morning it only tripped the first time I turned on the lights, similar cooler temperature. Now it's 80F and I cannot get either GFCI to trip by turning on lights.
    – ed729
    Oct 8 '20 at 18:18
  • Does it trip every time? Every time = shared neutral, which can get VERY confusing when GFCIs and switches are in close proximity. Oct 8 '20 at 18:28
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    Cold & DAMP! Dampness could leak just enough juice in a partially compromised circuit to trip the gfci. I think about all you can do at this point is start disconnecting lights and see if the problem stops. Since it's so intermittent, this will take time, but I don't have any other suggestions. Oct 8 '20 at 22:20
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I found disconnecting one of the fluorescent lights solved my issue. The light is hanging on the ceiling with a metal chain, then to a metal hook through the metal ceiling panel. Maybe some ground current is leaking into the metal panels of the building causing the GFCI to trip on other circuits, or maybe something with the emi. Either way I’ll be replacing the light and the issue is resolved.

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