It's earth leakage from the heating elements in the immersion and or
dishwasher - fairly common, I'm afraid. The fridge may have a small amount
due to RF interference suppression, and might just top up the amount
needed to trip the ELCB.
Changing to an RCCD might well cure the problem, or could you re-wire the
immersion to a non protected circuit - there's no need for it to be so
*Parenthetical remarks (however relevant) are (usually) unnecessary *
Dave Plowman firstname.lastname@example.org London SW 12
Rusty nail through a cable bridging neutral & earth, or bare & tarnished
earth wire contacting neutral in the back or a socket, or some other
high-ish resistance neutral-earth connection on the affected circuit? Or
maybe the other circuit you plugged the dishwasher into isn't properly
earthed and the fault is with the dishwasher?
Although 1 MOhm is within the Regs, generally anything less than 2 MOhms
could suggest a fault developing if the test was done using a proper
insulation resistance meter, a normal multimeter doesn't test with
sufficiently high voltage. Having said that, I wonder what the
resistance of a rusty nail would be? Also, did you disconnect neutral &
earth from the CU before taking the reading? I'm a bit puzzled that you
got that consistently low a reading for all circuits, yet you're not
seeing problems on other circuits.
Depends on your earthing arrangements, for a TT (local earth rod only)
supply there isn't any bonding between earth & neutral, although if the
earth is connected to the company's earth terminal then this suggests
TN-S or TN-C-S, in which case I certainly wouldn't expect anything like
1 MOhm between earth & neutral. Sounds as if the earth-neutral bond has
come adrift, or it's actually a TT supply but the elec. supplier has
used the wrong kind of incomer for installation. But having said that,
your RCD trips when tested with an independent device, so it would seem
you're getting an earth from somewhere. Wierd...
I reckon you really need to do or have done some proper tests on your
installation - insulation resistance & earthing for starters...
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