GFI breaker tripping

[Bill Frieze]

I'm in the final stages of finishing my shop. First time posting. I'm installing all the lighting fixtures at this time. I have a 60 amp fused disconnect at the house meter 4 wire run about 75 feet to the sub panel with the ground and neutral bars separated 3 ground rods driven 8 feet apart grounding the sub panel. All lighting circuits are on 20 amp breakers. I have 8 Metalux T8 8' four bulb fixtures on one switch, my problem is when I initially turn these lights on it trips my GFI breaker in the house that controls the outlets in both bathrooms. Since this GFI is not on the lighting circuit my shop lights stay on. I can leave the lights on and reset the breaker without any tripping issues, I can then turn the lights on and off without tripping. If I leave the lights off for a period of time turn them on, it will trip the GFI again. Any Ideas?

 

[Milton Shaw]

I would recommend checking neutral in main box as you might be getting a feedback from the garage circuits. If nothing there then check each leg at the house to neutral and see if there is a problem with neutral from the power company.

 

[Executive]

Swap the GFCI breaker to an adjacent position either up or down on the panel. This will put in on the alternate "leg" and should correct the symptom of the GFCI tripping. You still need to track down the cause of the problem. Make sure that all the connections are correct on the breaker and that your grounded neutral bus in the sub panel is isolated, not just separated. You should NOT have any connection like a green screw or copper strap connecting the neutral bus to the panel enclosure. Check the connections of the neutral feeder at the main panel and in your sub panel. Make sure they are electrically and mechanically secure. I'm assuming that the garage is a separate building and not connected to the main house thus the ground rods, but not sure why you installed three. Two are sufficient to meet code. You might also check that one of those three ground rods did not damage an unknown underground circuit.

Chris