Re: Electric trip problem.

[Dave Plowman]

I have a 30ma earth leakage trip that is tripping every time a

> significant load (about 3KW) is applied to the "downstairs" ring main. > The immersion heater will always trip it, the dishwasher in heat mode > will usually trip it and I have seen daft things like the fridge trip > it. Note that if the dishwasher is plugged into a different circuit > but with all other appliances remaining 'as-is' the device won't trip. > This doesn't make any sense to me as the trip is seeing the same load > (and fault) regardless of which circuit is carrying the load.

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 protected, IMHO.

[Robert]

[Ade]

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...

HTH