Dedicated Circuit - Question About Consumer Units

Indeed, that was a factor in my decision making, but outweighed by the benefits.

Respectively, it is more than a bit tricky, iirc the deepest box is 47mm so little room. Is this an installation for which you were the client or did you undertake the work yourself?

As regards regs, my specific point related to spurs, not cable size, for which iirc, only minimum is specified.

Whatever the herd have done, this is much more about individual installations and general guidance. @Simon-in-Suffolk suggests other improvements like earthing, which is no doubt worth investigating; no experience, but to be discussed here at some point with excellent sparky who appears from time to time.

It’s now 10 years or so since I rewired my house. A few observations: my first electrician said he could do what I wanted (spur and separate consumer units) but he did not separate the earth; a couple of years later I rectified the earth situation, which resulted in an improvement in sound quality.

I live in a rural area, but farming enterprises frequently make demands on the supply. The substation is just down the road, but it does not trip the supply as much as it used to do ten years ago.

In summary, the regulations keep improving the domestic supply environment, but it’s worth ensuring the earth is as a good as it can be. Various electricians have made observations about the quality of the earth; some has advocated a grounding rod, but recently they note that the local ground does not improve on the step down transformer 20 metres down the lane, with the sub-station a few hundred metres down the hill. Of course, your situation will differ, but as @Simon-in-Suffolk says the quality of earth is more important than the consumer unit.

Whilst I am a qualified electrician, I was working in IT at the time, and it made more sense for various reasons to get someone in to do the job that I trusted. So you are right, I didn’t do it, and I’d imagine it would be difficult, although a times served electrician whilst they may huff and puff a bit, will find a way.

It’s possible that an electrician may refuse to run 10mm cable, possibly because he genuinely believes it to be unnecessary, or maybe because the cable run and connections are quite awkward, especially to a wall socket which would normally use 4 or 2.5mm. That of course might make the sparky insist that a 10mm cable is outside the manufacturer’s intended use of a wall socket, and therefore refuse to do it. Hard to argue with that given that they have to certify the installation.
It is, though, certainly possible to fit 10mm cable into most standard sockets. If you want a real challenge, try fitting two of them in the same socket, as required if you want to fit more than one socket on the same circuit. I found that quite a struggle, but still possible.

I had a couple of quite long chats about this with Steve Hopkins when he was Naim’s customer service manager. His recommendations were based on my actual system at the time, which he was aware of, and distance from the consumer unit.
He also mentioned that they had experimented quite a lot when wiring the main demo room, and his recommendations were based largely on that, plus other installations he had done subsequently.
Steve made a number of suggestions, but the main ones that, when I pressed him, he insisted should not be avoided, were:

  1. Use a separate consumer unit run by splitting the meter tails.
  2. Use a single 10mm cable for the whole system.

We did not, I admit, discuss earthing arrangements, beyond him briefly mentioning that while a TT arrangement may be best, it was probably outside the bounds of what was practically achievable in most homes.

It maybe permissible (or perhaps not i really don’t know) to use one run of 10mm to terminate within a T&E junction box that is positioned very near to where the sockets are, and then multi feeds of relatively short distance 10mm cables go from the junction box to each of the number of 2-gang sockets in use.

This would be easier to run one length of 10mm cable, and although this would involve extra connections within a junction box it would make each 2-gang socket connection very neat and straight forward, and what would appear a star earth arrangement.
The junction box type would need to be well engineered and fit for purpose.

I’m not sure if this method would be allowed at the end of a radial circuit (?)

Well then you get another electrician. I have never heard of a tradesman rejecting a customer requirement unless they didn’t want the job. Most electricians deliver to customer requirements as long as they are compatible with regulations and they are capable of implementing them.

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TT is relatively easy to achieve in most houses, with flats or maisonettes it can be more challenging if not impossible. If you have a hifi and a house, it’s one of the best mains related upgrades you can do if you have noisy mains.(in my opinion)

Also if you have a detached powered shed, outbuilding, or garage with metal fixtures which is distinct from your house by a certain distance, then I believe TT is usually preferable with each building having its own Earth electrode… where as your house can be TNC-S. this is because of the increased risk of electric shock in such applications using PME/TNC-S supplies and a risk assessment should be made in a new install. (ESQCR regs) Because of this for example some types of leisure accommodation, static caravans including caravan parks and boat yards/marinas are specifically prohibited by these regs in the UK from using PME/TNC-S earthing because of the significant increased shock risk.

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I believe it’s allowed. It comes down to size of RCD, floor space served by the radial, and radial wiring size, and anticipated load. With 10mm wiring and hefty RCD in a domestic room I can’t see an issue. You won’t be plugging kettles into the radial. For multiple high current devices separated out then a radial is often preferable. Low current devices together clustered together a radial is fine, and is often cheaper to provide… though I say because of the large inductive current in rush with large transformers in hifi amps, if using radials use as large a cable as practical and 10mm is going to work fine.

Agreed, although a couple of electricians I’ve spoke to were reluctant to use 10mm cable on the basis that the intended use of a wall socket would be for thinner cable. For example, MK say their sockets will accept cables up to 6mm, so squeezing in one, or even two 10mm cables could be deemed outside of the manufacturer’s specification. Apart from the tight fit in the connection, pushing those stiff cables into even the deepest back box requires some force, which is not ideal.

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If you look on the manufacturers website, most detail the cable size capacities for terminal.

For example, I used Schneider un-switched sockets and they state 1x 10mm2 or 2x 6mm2.

My electrician went with 6mm2 runs as I had two double gang sockets.

DG…

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Very interesting article and thanks for your high level knowledge Simon. I hope one day to have a new build done for me in West Sussex area. I would have Solar battery heat pump etc. Probably Givenergy All in 1 or Powerwall 3 maybe. I need to google but TT is a separate earth rod?. Is this a good idea for new build?. Separately is the diagram showing separate cables to each socket i.e 3 10mm for 3 double sockets. What are the breakers 32A spd for each (sorry only basic electrical knowledge). New build means best quality consumer unit. If deeper socket boxes then noggins can be set further back to accomodate I assume

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