GFCI Outlet Trips with Lights or Fan Switch

[jdf405]

My bathroom was remodeled about a year ago, with a new 20A line pulled from the panel. The lights and fan are on the line before the GFCI outlet. We leave a rechargable tooth brush plugged into the GFCI all the time, but nothing else.

Recently when we turn off the lights or the bath vent fan the outlet trips (GFCI, not the 20A breaker). It resets right away easily. All of the wiring was per code, inspected, etc... and I've tested the resistance from hot & neutral to ground with an Ohm meter and its above 1 MOhm (the highest my DVM can read).

Any ideas on why this happens? Possibly a defective outlet?

Thanks for the help,
Jonathan

[1960 rancher]

Your stating that the outlet trips when shutting off the light or fan? Seems odd but it could put a surge on the neutral causing the outlet to trip. I would replace the outlet and or confirm there is not a short between the neutral and ground. Not sure what the threshold is for a trip but it could be around 1mega ohm.... If your meter does not go to OL (everload or open) then that could be your problem. Is the tooth brush unplugged when taking this reading?