[R-390] GFCI issues

[Jim Haynes]

I'm having a somewhat similar problem.  Older house, but new outlet
with a GFCI breaker installed for the washing machine.  About once a
week the GFCI trips in the middle of the night.  Even with the washing
machine unplugged.  And I replaced the (ordinary) outlet at the machine.
At first that seemed to help, but then the GFCI tripped again.

What I plan to do next is get an AC milliammeter and see how much
current flows from the breaker to the Romex with nothing plugged in.
And also use a variable resistor to see how much current it takes
to trip the GFCI.

An ohmmeter shows no leakage on the Romex itself.  A friend suggests
using a Megger (an ohmmeter that uses a high voltage source).  I
did try an improvised megger, in the form of a capacitor tester that
applies a high DC voltage across the capacitor under test.

Jim W6JVE