Split load consumer unit

[Charlie]

I'm about to fit a new consumer unit to replace two 'orrible old rewirable fuseboxes. I've bought a split-load unit, but I'm a little unsure how to split the MCBs between the sides protected and unprotected by the 63A RCD.

I'd like to put the following on the protected side:

32A - spare for eventual new spur to shed, possibly via a new small CU in the shed 32A - socket ring main 32A - electric shower and possibly another 32A for the kitchen ring main (in which case I'll have the fridge/freezer on another circuit for obvious reasons).

The question is, seeming as the RCD is only rated at 63A, is this sensible? Will the RCD act as a circuit breaker as well as a residual current breaker and trip if the combined current from the above is

63A, or do I run the risk of taking too much current through the RCD as the total of the above MCBs is much higher? I suppose I can always just have the socket ring and the outdoor spur protected, but I'd like to have the shower protected as well (having seen how it was originally wired I'm keen to protect it as it made me very nervous- even though it's a lot better now).

TIA

Charlie

[Lurch]

On Fri, 09 Apr 2004 12:36:01 +0100, in uk.d-i-y Charlie strung together this:

Sounds about right.

No, or yes! What size is the main service fuse in your property? The RCD and all CU components should be rated to this value.

Not in reality, but technically any installation will be the same.

[Owain]

"Charlie" wrote | I'm about to fit a new consumer unit to replace two 'orrible old | rewirable fuseboxes. I've bought a split-load unit, but I'm a | little unsure how to split the MCBs between the sides protected | and unprotected by the 63A RCD. | I'd like to put the following on the protected side: | 32A - spare for eventual new spur to shed, possibly via a new | small CU in the shed | 32A - socket ring main | 32A - electric shower | and possibly another 32A for the kitchen ring main (in which case I'll | have the fridge/freezer on another circuit for obvious reasons). | | The question is, seeming as the RCD is only rated at 63A, is this | sensible? Will the RCD act as a circuit breaker as well as a residual | current breaker and trip if the combined current from the above is | 63A,

No

| or do I run the risk of taking too much current through the RCD | as the total of the above MCBs is much higher?

Yes, in theory.

Might be better to feed the shed from a non-RCD protected circuit and have RCD protection in the shed's CU. That will avoid a fault on the shed circuit taking out the house sockets.

Owain

[Dave Liquorice]

I'd go for either a separate RCD box in the house or better an RCBO on the unprotected side of the CU. Don't the regs specify that any power circuits leaving the "equipotential zone" have to be RCD protected before they leave or is that just for sockets that may have applianaces used outside connected?

Definately a good one to avoid.

[Dave Liquorice]

No, an ordinary RCD is a for earth leakage detection and supply disconnection only. The 63A (or WHY) current rating is the current that it can (reliably) switch without excessive arcing or the contacts welding together. Not quite sure how this fits in the few kA that will flow for the few mS required to trip an MCB or RCD with a direct L E short...

In theory yes, check out the section(s) of the regs regarding diversity and expected loads etc.

[Charlie]

Thanks for all the suggestions; I think I'll run the socket ring main and electric shower off the protected side for now and sort the shed out later.

Charlie