I tracked down an AC appliance (a dishwasher) which started tripping my home current circuit breaker (RCD). I happen to have a professional insulation resistance meter and I was able to measure about 10× difference in insulation resistance when switching its polarity.
Before doing anything, I try to understand whether this can be a sign of failure of power input circuits.
What I see when attaching meter terminals (+/-) to the appliance terminal (L/N/PE):
L (+) <-------> PE (-) : 113 MΩ
N (+) <-------> PE (-) : 113 MΩ
L (-) <-------> PE (+) : 1.3 GΩ
N (-) <-------> PE (+) : 1.3 GΩ
Measurements carried at 250 V.
The values can be consistently reproduced.
For non-European readers, according to European standards (images via Google):
- L = live (brown)
- N = zero (blue)
- PE = protected/earth (connected to the chassis of the appliance) (yellow/green)