RCD keeps tripping when shower switched on

Killeavy7138 · 7 Feb 2007

Hi Looking for a wee bit help here

I've installed a 10.5kw Gainsborough shower using 16mm cable as it is a wee bit of a long run. There is a 50A circuit breaker in the RCD side of the split consumer unit. The RCD is rated at 80A 30ma. Also on the RCD side of the CU are the cooker (32A), and two ring mains at 32A each. When switching on the pull switch in the bathroom everything is fine. As soon as the shower on/off switch is turned on even at the lowest temperature the RCD trips. Tried switching off other circuits on the RCD side but the same thing happens. I meggered tail cable between cores and earth and it's ok. The bonding on the pipework has been renewed too. I'm convinced it's the shower any ideas on how to check this or any other ideas as to what could be the cause. (The CU is a WYLEX).

Many thanks
Killeavy

jj4091 · 7 Feb 2007

disconnect the shower insulate the wires & try again to switch on the power,if it does not trip then the problem would appear to lay with the shower

Spark123 · 7 Feb 2007

Check the neutral is in the correct neutral rail in the consumer unit first

.

Killeavy7138 · 7 Feb 2007

Thanks i was wondering about the neutral as i am getting a slight potential difference between earth and neutral. between 0.5v and 1.2v ac.

Steve · 7 Feb 2007

Killeavy7138 said:
Thanks i was wondering about the neutral as i am getting a slight potential difference between earth and neutral. between 0.5v and 1.2v ac.

I'd not worry about that. You checked the neutral is in the right bar yet? There are 2. one for RCD protected, and one for non-RCD.

Taylortwocities · 7 Feb 2007

Yes, dont fotgrt that switching off an mcb only breaks the phase conductor but the RCD monitors phase and neutral. Only way to check for sure is to remove both conductors from the consumer unit terminations.

Re your OP. The RCD rating of 80A is the operational rating of the contacts not an overload rating. If I was doing this I would have a separate ccu (RCD&50A breaker) for the shower connected to the supply by Henley block.

Something in the back of my head says the limit for a circuit is 45A. Anyone remember? SS??

TTC

securespark · 8 Feb 2007

Manufacturers vary.

Wylex say their boards (with main switches rated <100A) are not designed for any device over 32A.

The NH range I have just been told can happily accommodate more than one device in excess of 40A, "as long as you apply diversity and the total load on the CU does not exceed 100A".

GE used to say you can fit no more than one 40A MCB in their boards.

Might be worth ringing round a few more manufacturers to double check.

mapj1 · 9 Feb 2007

Assuming no crossed neutral cock-up
You have megger - unship the wiring and connect the megger between the earth terminal of the shower as one side and the L&N terminals strapped together as the other. Effectivly this does a 500V PAT style insulation test, - this should do no harm if the shower is in good nick, as no over voltage is applied between L and N but will it seek out any element to casing weakness. Expect a megohm or so, if you see much less complain to the makers, as you've been given a Friday afternoon one..

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RCD keeps tripping when shower switched on

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