How do I distribute the loads on a 7th edition consumer unit?

[clangers_snout]

I'd be grateful for any help with distributing the loads between the two RCCBs on my 7th edition consumer unit.

I have:

1 radial upstairs lighting 1 radial downtairs lighting 1 upstairs ring main 1 downstairs ring main 1 kitchen ring main 1 radial oven circuit 1 shower circuit 10kW

[Phil]

I expect 7th ed. had knife switches, not RCCBs.

[clangers_snout]

Ah yes Phil I missed the 1 off! Now anything constructive to add?

[John Rumm]

What is the maximum current load on the RCDs?

The usual approach with only two RCDs is to mix the downstairs lighting with upstairs sockets:

RCD1

I would put the kitchen ring on this one so that you have a way of isolating sockets downstairs but still having power available.

Keep the oven with it

RCD2

Which leaves the shower here

[clangers_snout]

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Thanks for that John. However I don't think I can put the oven on the kitchen ring as all the wire sizing guides I have seen require more than 2.5mm T&EI Also I'm not sure having the shower and the upstairs lighting on the same RCCB is wise as if the lighting goes it leaves you in the shower in the dark.

[ARWadsworth]

I'd do the same apart from the oven. I would put it with the downstairs ring and upstairs lights.Although is probably does not matter.

I would put the shower on a different RCD to the boiler (whatever circuit that is connected to).

[ARWadsworth]

I believe he meant put to the oven MCB on the same RCD side as the kitchen ring.

It does not matter. If the RCD for the lights trip whilst you are in the shower then you are going to be in the dark in the shower! One way leaves the water running the other stops the water!

[John Rumm]

I was not suggesting changing the wiring - just placing your oven circuit on the same partition of the CU as the kitchen ring.

[Scott]

I am not an electrician but have just had a new consumer unit installed by an electrician.

The way we did it was to have an individual RCBO for every circuit. That means a trip on one circuit will only affect that circuit.

[ARWadsworth]

But at a cost. How much did that set you back?

[Scott]

£590 (for nine RCBOs).

[ARWadsworth]

That's not a bad price. What make was it?

[Scott]

Crabtree. The price covered parts and labour. AIUI you would require eight RCBOs so yours could be slightly cheaper.

Once the electrician got over his initial surprise (I nearly said shock!) he agreed it was the 'way to go'. I just like the idea that if the washing machine goes faulty it won't cause the computer to crash.

[clangers_snout]

I agree that it's nice to have that protection individually for each circuit but cost wise it's not comparable. My 17th ed. consumer unit with two RCCB and 10 MCB cost about =A360!

[David Robinson]

We were thinking about RCBO(s) to protect the fridge and freezer from defrosting if a trip happened while we were away.

But the cost of the RCBO(s) was more than the value of food in the fridge, and comparable to the value of food in the (upright) freezer. Considering it had never been a problem before, this seemed rather an expensive "insurance policy" for such a low risk and low value event.

To cover the potential lack of light when a light blows, an MCB and/or RCD trips, or there's a power cut, or I intentionally switch off the circuit(s), I added emergency lights in the hall.

Cheers, David.

[Chris R]

My neighbour lost the contents of his freezer and a pondful of coy carp when a light bulb blew in an outside light while he was away on holiday.

[ARWadsworth]

There is the inbetween option. RCBOs for a couple of circuits and the two RCDs for the rest of the circuits. Probably adds £50 to the installation. I use such setups when there are dedicated outdoor circuits.

[John Rumm]

Yup, I was about to suggest the middle ground option... There are a bunch of circuits that are highly unlikely to present trip hazards, and others that are far moire likely. The unlikely ones can be distributed about the pair of RCDs on the nominal "17th edition" (i.e. cheap 'n' basic) CU, and then any likely problem circuits given RCBOs.

[John Rumm]

Nicely illustrating why having outdoor circuits protected by the same RCD as anything in the house is not a good policy.

[Scott]

How long will it last? Say 20 years. £30 per year. 60p per week. Quarter of a pint of beer. I bet you spend far more than that on other non-essentials.