"northern_relayer" wrote
Are you the OP formerly known as "the yorkshire dalesman"?
| That is because there is the possibility they may be used for
| outdoor equipment. Sockets which 'may' be used to power outdoor
| stuff MUST be RCD protected.
| that's what I understood, but if they are labelled 'indoor use by
| computer/hifi/Tv only' & the sockets are a different colour (eg
| yellow/blue/red) is that enough to make them 'not likely to be used
| outside?

I don't think it is. The colour of the socket is meaningless in terms of the
regulations and a 13A socket should be suitable for supplying any equipment
usually fitted with a 13A plug. This is why 13A sockets should not be fitted
to 6A lighting circuits for table lamps and the like.

The spirit of the regs is clearly to ensure that equipment used outdoors is
very likely to be plugged in to an RCD-protected outlet. If a dedicated
RCD-protected outlet marked 'for external equipment' is provided in
convenient places as required, that is likely to be used in preference to
any other and thus the reg will be satisfied, AIUI.

| I've lost (open) files several times by running the computer off the
| RCD circuit (eg Excel can corrupt files it has open if the switch is
| thrown). Since moving it onto the fused ring there's never been any
| trouble.

You might want to consider a small UPS for the PC, especially if you're in a
rural area where overhead line failures are foreseeably more common.

| Both circuits test completely Ok for insulation & earth - neutral
| short. Nuisance tripping comes mainly when certain tools (all double
| insulated - so no earth) are run off the rear fused ring - only the
| tools keep going but the front CU is the one that trips. Observation
| suggests overload is the cause - an extra thick hedge twig or heavy
| pressure on the hand sander.

Overload shouldn't trip an RCD because RCDs don't trip on overcurrent, only
on a current imbalance caused by earth leakage. Anyway, you obviously have
problems with your wiring and with rewireable fuses are well overdue for a
rewire.

| So what's happening? & will Christian's solution of an RCBO for each
| cct cure it?

RCBOs on each socket circuit ideal but a bit expensive. Split-load CU is
usually an acceptable compromise, especially if workshops and the like are
run from the non-RCD side and given their own local RCD protection.

You need an RCD on the workshop sockets for the same reasons as anywhere
else, only increased: handheld power tools, risk of abraded or cut flex, wet
hands, etc. Just don't have the lights on it.

Owain