On Mon, 09 Jul 2007 06:28:29 +0100 someone who may be Terry Pinnell
wrote this:-

Thanks for those prompt and helpful replies. I'm responding to the
requests for more info:

The unit is a modern Crabtree 'modular' control unit, and carries a
label showing it has a sensitivity of 30mA. [snip]

RCD PROTECTED CIRCUITS:
-----------------------

1. Immersion heater. (This is the one that tripped.)

This should have been put on the non-RCD section. If you are capable
of doing it properly, remove the MCB and put it in the spare way on
the non-RCD side.

You haven't said whether the heater was (due to be) switched on, or
not, when the RCD operated. As has been said it might just be that
the immersion heater sensitised the RCD and there was another fault
which actually caused it to operate.

It is unlikely that a fault developed on the fixed wiring to the
heater. More likely the heater element has a less than ideal
resistance. I would disconnect the immersion heater cable at the
point where it joins the fixed wiring before going on holiday, if I
had not moved the thing to the non-RCD side.

After the failure I thought *all* power was lost. But now I can't be
100% sure whether I had the lights on, and I don't recall checking
them. Certainly things like fridge, microwave, etc were off.

As all these circuits were off it is likely that the RCD operated.
This would have removed the supply from all the circuits on the RCD
side of the unit, but not those on the non-RCD side.

The only switch I reset in the Crabtree unit was the RCD one
controlling the immersion heater.

The RCD controls electricity to all the MCBs on the RCD side of the
unit. It does not just control the immersion heater.

When you have read up the differences between MCBs and RCDs and how
they are arranged you may be able to give us more precise
information.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54