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Full house rewire or leave wiring as is with new RCBO CU?

Stewarty

Hello,

I would be grateful for some advice with regard to a rewire and CU upgrade after an EICR and because of the age of the installation...

We recently had an EICR done on our property by a rather young Electrician. The Electrician flagged up a couple of items that need sorted out. No RCD on lighting circuits and the 40amp mcb down to a 32amp mcb for cooker circuit on a 6mm cable. He said we need a full rewire and the CU needed to be updated. The cabling is all in old red and black within the grey coloured PVC twin and earth.

We have only one RCD protecting 2 x 32amp 2.5mm rings for all the sockets in the house including the kitchen, gas central heating boiler, 1 extractor fan on a spurred FCU , 1 spurred FCU outdoor socket and 2 spurred FCU outdoor lights. Oven and Hob on a 6mm radial on the 40amp mcb. 10.5kw Shower 10mm radial 50amp mcb. All the lighting circuits are on the non-RCD side of the single split board on 6amp MCB's, with 1 Extractor Fan with no isolation but on the lighting circuit too. We have a single cooker switch above the worktop for our inset worktop Hob and built under worktop Oven.

The Electrician said the cooker circuit was against the regulations. Both the Hob and Oven are supplied from a single gang double outlet plate below and behind the oven. He said that they could not be supplied by one cable from the CU.

I don't really know this Electrician his name was passed onto me from a builder I met on a site. He is registered with the Niceic. The Electrician I would have normally used who I have known for years, is no longer in this country and lives overseas. I contacted him and forwarded a copy of the EICR report and he flagged a couple of issues with the report. After a few chats with him he said that it looks like the the young guy is not quite up to speed with the regulations judging by his report.

When I was at work, the young guy was at our house for just over an hour and charged £125.00 My mate says he has not done a complete and proper EICR on our house considering to do it properly would have taken at least half a day and should have cost more than he charged.

I have since found another Electrician who is happy to do all the work and he has been recommended by a friend.

Our property is a 3 bed ground floor flat built in 1888 stone building. By all accounts, a rewire was done and a new metal CU was fitted in the 1980's. There's no paperwork but the CU has a label on it saying; Type tested to B.S.5486, Part 13, 1989.

We had the DNO out in 2019 because I thought the Head looked a bit dodgy. Black stuff was leaking out of it. They surveyed it and replaced it immediately. The DNO Electrician said it was an old bitumen head and they replace them as a matter of course upon discovery. He also fitted a new double pole isolator on the tails and renewed the Earthing.

The kitchen has a lowered plasterboard ceiling and all the wiring drops from above. I assume because there's a concrete floor.

The bathroom is right adjacent to the kitchen and has a tank cupboard fitted in the corner. All the cabling for the kitchen comes under the floor from the CU and up through the tank cupboard in a corner box. At the top of the box there has been a removable access panel installed. This also acts to hide a huge hole in the dividing wall into the kitchen lowered ceiling void where all the cables go through and run around the walls dropping down at various points. The cabling to the kitchen is 40m from the CU. All the internal walls are brick or stone.

From previous investigations that were done by British Gas when we had a new boiler fitted. They said all the wiring in the house is shielded with 50mm wide galvanised capping lengths so the guys found it easy to pull-in new cables. They done away with one of our double sockets that was sitting below the new boiler location in the kitchen corner and used it for boiler wiring. 

We intend to fit a new full RCBO CU but, should we rip-out all the older wiring and replace this too?

Another thing... The great debate about kitchen final ring circuits on 2.5mm 32amp mcb.

Should we change it to a 32amp RCBO 4mm circuit instead of a ring seeing as we intend to fit a full RCBO CU?

Cable is not an issue. I can get a 100m roll of 2.5mm, 100m roll of 1.0mm and 50m roll of 4mm. And numerous half rolls and the like... My old friend says I can go round to his Dad's workshop and get whatever cable I need. It was left there when he went abroad. I have agreed an excellent price with him.

Well, that's about it... any advice welcome.

Thanks

  • in reply to Stewarty

    "potentially 50m of cable saved in converting to 4mm radial?" well if you want to rewire the circuit anyway then yes it is one consideration but if you want to leave it as it is (and it is OK?) then you save even more cable by not renewing it. 

    I do understand mapj1 ducking out before he writes a short book, comment. That`s why my answer was so short. I agree with what he says

  • in reply to ebee

    Yes haha...point taken...

  • "potentially 50m of cable saved in converting to 4mm radial?"

    Also add in that a length of 4mm² typically costs more than two lengths of 2.5mm², and if the load is reasonably shared between the two 2.5mm² the cable losses (and hence voltage drop) will be less than with a single 4mm².

       - Andy.

  • in reply to AJJewsbury

    Thanks Andy...

    Yes another perfectly valid point!

    I'm beginning to think that this Radial idea isn't so good after all...

    Presumably; not as flexible for the twists and turns, more hassle in back boxes, more trouble to terminate at accessories and at the CU. And as said, cable losses are worse, cable is more expensive in the first place. I'm sure there are a few other problems with a 4mm radial.

    In truth, could it be that the UK has it right and the rest of the world are sadly lacking behind?

    For example, when I went to visit a Dutch Navy friend in Holland, I could not believe how shoddy and dodgy looking his house electrical installation looked. I noticed this in a few places I visited. I especially didn't fancy the fact that all the sockets were at waist height because of the flooding...

    Maybe we have the right idea here and the Radial thing is just lazy thinking?

    My Aussie friend has a lot of questions to answer...

  • If it is already there and working well, there is almost never enough difference in practice to warrent changing it to the other, whichever way you are going. But your comment about stiffer wire is certainly true - I suggest wiring up in 4mm² in a standard depth single socket back box is not for the faint hearted, and by the time you want a fused spur for something I suggest it is not really possible.
    In cases of cable fest, though mostly to be fair in relation to heating controls, I have been known to mis-use a twin back box of the kind that takes 2 single plates and put a blank face on one half and the actual item on the other, and hide half the spaghetti junction behind the dummy plate. But then I am also someone who has put a dummy box with the back slotted and bank face in the line of an otherwise concealed cable  purely to reveal its presence to avoid the 'cable out of safe zone' problem.

    (when the situation is already set up for you by what has gone before, then to put it 'right'  there is not always an ideal choice, and queue that song from Matilda the musical,  'sometimes you've got to be, a little bit naughty...' )

    Mike.

  • in reply to mapj1

    I think Mapj1 was referring to the dual boxes rather than the twin boxes - two single boxes as far as fixing points etc are concerned but actually mounted as one backbox. You can also get them as a twin and a single in effect too. Yes they are very useful

  • I'm not sure 4mm² is particularly stiffer than 2.5mm² - the 4mm² being stranded while 2.5mm² being solid (in T&E at least). It's certainly bulkier and perhaps springier which can make it more difficult to dress nicely and squeeze into shallow back boxes and while all 13A socket terminals accept 3off 2.5mm² conductors, quite a few don't accept 3off 4mm².

      - Andy.

  • in reply to AJJewsbury

    Yes not that much bulkier or stiffer...

    Found these. Top from Prysmian Cables and Bottom from Doncaster Cables.

  • in reply to Stewarty

    Now how about this...

    Looking at the EICR report

    Why no insulation resistance testing?

    Are these items a C3?

  • in reply to Stewarty

    2. No RCD protection - fair comment. Recommending CU replacement is a bit steep (EICRs are meant to identify problems rather than dictate particular solutions).

    3. 'dated' of itself does not endanger the safety of the installation (some older accessories are actually better built than modern equivalents) - so unless they're damaged or to such an old standard they they'd no longer be considered safe etc - it's nonsense on a BS 7671 EICR.

    4. I'm not sure if being 'supplied of the same cable' is being reported as an issue, or just a means of identification. If the MCB is rated higher than the cable (and overload protection is required, which it usually would be as we don't relay entirely on diversity), then the bit about downrate or replace cable could be fine.

    5. see 3.

    6. The reg is being taken out of context - 701 series only apply to bathrooms.

       - Andy.

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