In article ,
"Ben Blaukopf" writes:

I don't know how I concluded it was dead yesterday. It's now back to
tripping. I measured the resistance across live and earth and got over
1Mohm.
Neutral is effectively completely isolated. So surely the current leakage
should be
less than 30mA and the RCD shouldn't trip (it goes as soon as I flip
the switch on the connection unit)? I realise I'm probably missing
something...

The resistance might look quite different with mains across it.

An oven doesn't need to be on a 30mA RCD, and the metal sheathed
mineral insulated elements when cold are allowed to leak, which
means it's not a good idea to have it on a 30mA RCD or you can
never warm it up;-). You would normally only need it on any RCD
if the supply is a TT type, in which case it should be rated 100mA
or more.

When PAT testing a non-portable appliance with metal sheathed
mineral insulated elements, if the leakage is too high, you
are supposed to repeat the test again having run the appliance
to warm up the element. This issue most often arises if the
appliance hasn't been used for a while.

--
Andrew Gabriel