RCD is MEM 100A 30ma RCD - *with 3rd earth tail* connected
o MCBs all OFF -- no L connection to house
o RCD-N-output disconnected -- no N connection to house

RCD still trips instantly.

I found this after:
o RCD would not reset - all MCBs off
o RCD would not reset - all MCBs off & all appliances dbl-pole off / unplugged
o RCD would not reset - all MCBs off & most cables L+N disconnected
o RCD would not reset - all MCBs off & RCD N-output to N-bar disconnected

So I'm sort of running out of options.
I don't understand how it can trip with no L connected or N connected.

The meter also powers a separate RCD for outside lights, skt, shed.
So I'm powering fridges & a few backup items off that for now.

Q: Does this sound like a faulty RCD - only 7-10yrs old?

No call-out available tonight :-( *blink* *blink*