I have a strange problem : when it's raining heavily, the RCD breaks on one line. It is quite large a differential : 0.3 A.
This is in a country where effective voltage is 230 V.
There are quite a few lights on the offending cable. But they are all internal except 2 that are outside, but well sheltered (they are not getting wet):
As you can see, it is exposed wires, outside, so it seemed a reasonable guess that these were the offenders. I took my multimeter, and measured the voltage. I was surprised to see that even when I turn the switch off, I still have a voltage of 1.2 V in these cables. This surprised me.
Is it normal for these to have a low voltage even when switch is off? Could that be what causes my RCD to break? If this is abnormal, how do I go about fixing it?
PS: (I have read other questions about phantom voltage, but my question pertains to the RCD breaking in that context)