Updating house electrics - opinions requested

P

pna

I've recently moved into a 1970s house and we have an old 6 way Wylex CU with fuse wire, but the wiring itself is the grey plastic covered type. I am considering improving the safety of the installation with MCBs and/ or RCD protection.

The 6 circuits are: cooker, downstairs ring, upstairs ring, garage (radial), upstairs lights, downstairs lights.

My understandings, and where I am seeking confirmation, is that RCD protection would be best for the garage circuit, and parts of the downstairs ring where I might plug in items I use outdoors (like a lawnmover).

I had thought about a new split load CU, but there are areas of the downstairs ring where I understand I would not want RCD protection - study containing my PC, the kitchen - contains fridge, freezer, washing machine. To overcome this would require splitting the downstairs ring, which sounds expensive in terms of time, effort and cost.

So the solution I wanted to sense check was to get an additional garage CU with RCD - this would be inserted into the exisitng radial circuit, and replace 2 sockets at the front & rear of the house where we use the lawnmover with sockets that have permanent RCD protection. On the original CU, I would also replace the fuses with plug-in MCBs.

Is this a reasonable plan or is there something wrong with it?
 
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I hear the voices of derision already … but if I was you I’d start by getting a professional in to check the existing wiring or even get a proper a Periodic Inspection Report. They will be able to spot any problems that need fixing (as opposed to the nice to haves.).

Updating bits can be false economy if it latter turns out that the core installation is shot to bits. I’m not saying your is … but its worth a check before starting to spend money.
 
P

pna

The electrics have been professionally updated in the past couple of years - the garage circuit, and the downstairs ring for the extension - so I'm not expecting there to be major problems...but I've already had quotes for a PIR but wanted to be able to measure whether any suggested solution is appropriate and good value. I have no intention of installing a new CU myself - too close to permanently live electrics for me.
 
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If you are changing the cu why not use a RCCBo for the garage circuit, this will do the same job as an rcd/mcb & will save you having to have a split load cu.
Then use a plug in 30mA rcd at the socket when using the mower on the downstairs ring.
Having said all that it does depend on the type of incomming system you have, if it's TT it should be a split load cu (100mA 100A time delay for main switch & 30ma for the split load side).
 
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pna said:
I've recently moved into a 1970s house and we have an old 6 way Wylex CU with fuse wire, but the wiring itself is the grey plastic covered type. I am considering improving the safety of the installation with MCBs and/ or RCD protection.
pna said:
The electrics have been professionally updated in the past couple of years - the garage circuit, and the downstairs ring for the extension

Sorry, But it doesn’t really sound up to date. 6 way re-wirable fuses – I’d have expected an updated system to have a new CU and an RCD. A professional update would have complied with BS7671. It has required RCD’s for sockets capable of supplying external appliances since 1991. Do you have an immersion heater? If so where is it supplied from – the upstairs ring??

You are very wise to get a sparky in to do the work. Get them around to quote and they will advise the best options. If they do a full PIR they may discount it against any remedial work.

I’d replace the old CU with a new split load one. You can put the lights and cooker on the non-RCD side. (Add a Immersion circuit if needed too). The rings and radial on the 30ma RCD side. If you are worried about the fridge/freezer/study 4/5 options are:-

a) Don’t worry lots of other houses have this arrangement.
b) Put in a new non RCD protected radial for the fridge/freezer.
c) Use an RCBO for the Kitchen/Lower Circuit on the non RCD side
d) Split the ring. Not necessarily hard if you have wooden suspended lower floors.
e) (If the sparky agrees its ok in your installation) Put the lower ring on the non RCD side.

Hope this helps.
 
P

pna

Thanks b-n.

I meant the installation had been modified in the past couple of years, not that it was up to date. I can see a few things I believe are wrong myself such as no isolation switch for the cooker (it looks as though it has been moved - the original isolation switch works the gas hob), plastic boxes on the garage sockets, and no RCD protection. It also does not have MCBs for convenience. BTW, I don't have an immersion heater and we have a gravity fed shower. I've looked at my meter and if I interpret the reference diagram correctly, I have a TN S supply. I think I have a 60/80A Henley block, so I guess this too is not up to today's standards.

It looks as though a new CU might be better future proofing as we are planning on an en-suite with shower at some point. How many 'ways' is it normal to provide for a 4 bed house?

Out of interest, could you explain how option (c) would help?
 
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if the CU is a wylez standard (plug ins) you can't fit a rcbo anyway
 
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Option “c” was to use an RCBO. RCBO’s combine the protection of an MCB and RCD into one device package. This allows the circuit to have its own RCD protection. In effect I fused on a non RCD side circuit it allows it the benefit of RCD protection but without the nuisance of tripping or being tripped by other circuits.

If you want to minimise trip nuisance you can use RCBO for each socket circuit. However it’s a lot more expensive.

Also it’s worth pointing out that some makes of RCBO have a “C” curve MCB profile. This makes them less suitable for domestic installs.

For a 4 bed house I’d estimate 12 ways (that’s 6+6 split load). Asa guide you might have 1 shower, 1 cooker, 2 rings, 1 immersion, 2 lights + space for garage, sheds, Jacuzzis etc.

(RCBOs are shown below courtesy of ryanj neat work - they are the taller breakers.)

installation_bus.jpg
 
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pna said:
How many 'ways' is it normal to provide for a 4 bed house?
You really do need to plan for what you want. I'm planning a refresh of my installation, 3-bed house, and I'm up to 14-15-16 circuits.

Allowing for a few spare ways, and the space taken by incomer, RCD, other rail-mounted stuf like contactors, bell transformers etc, I've got a 40-module board taking shape. A bit OTT, but I got it cheap.....

Remember that an "n-way" split-load CU may only give you n-4 spaces for MCBs...
 

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