10mm dedicated mains supply, but is a separate CU really necessary?

I am having a full re wire in my 1970’s bungalow. Like many of us have found, my Electrician nearly wet himself when I requested a separate, dedicated 10mm radial circuit for my Naim black boxes. He has agreed to do the work.

When I also requested a separate Consumer Unit, he told me that it was a complete waste of money, as the 10mm radial used the same ‘dirty electrics’ entering the property.

I’m interested to know, those who have opted for a dedicated mains supply, have also opted for a separate Consumer Unit, or used a 32amp type C RCBO in the existing board?

In the final stages of building a new house, all these issues have recently come up.

Need? No. You do not need anything, including a dedicated circuit. Does it benefit? Yes. But how much will depend on how sensitive your system is; what you consider a big improvement; and how expensive it is to have the work done. That equation is going to vary greatly from person to person.

My view, and others may disagree, is that the order of precedence for sound quality is as follows:

  • Dedicated radial
  • Dedicated radial + isolated earth (not shared with other sockets) back to the building earth
  • Dedicated radial + dedicated earth (rod or plate, whatever is standard in your country)
  • Dedicated radial with audiophile MCB + dedicated earth
  • Dedicated CU (normal MCB) + dedicated earth
  • Dedicated CU with audiophile MCB + dedicated earth

I’d always tackle earth quality as the next step after a dedicated radial before thinking about separate CUs or fancy MCBs. As far as the 10mm mains goes, I’d probably rate that in terms of importance as something worth doing after an isolated earth (common building earth but earth on that radial not shared). On the other hand, it’s actually a minor expense. The labour to fit that cable costs far more than the cable itself.

I’m currently doing the Dedicated CU with dedicated earth but no audiophile MCBs - assuming the electrician and I can stop arguing about 101 other non audio related things and I don’t sack him first :grimacing:


My first attempt at dedicated mains took a spare slot in the main consumer unit. It was a wate of time in terms of sound quality.
After a conversation with Naim support I followed their recommendations, including the use of a separate dedicated consumer unit. Yes, it gave me a very significant improvement.

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He may have a point, i find the SQ of my system rises considerably in the off peak times of the late evening and early hours of the morning. This is something we have no control over or ability to change.


The 10mm has nothing to do with quality of current. It is about lowering the resistance.

0.75mm might be rated fine for 13A and 2mm might be the common diameter used but they have very different resistance characteristics. As does 10mm. It’s not about how much current you are drawing. It is about how fast you can recharge the caps and on transients, those requirements are in microseconds and resistance will affect that. It is unlikely that the electrician is considering that.

My electrician happened to also be an audiophile so he was the other way. He really wanted to push for additional stuff that even I did not care about.


Guess there are very interesting debates over there :sweat_smile:

I have a dedicated CU but not from the meter tails. I have a 3 phase supply and it must (legally) be separated to single phase in the main CU. My 6mm feed comes from there to a dedicated CU and it made a significant difference. Subsequently fitting specialist audio breaker (GigaWatt) and RCD (Doepke) made at least as much difference again.

No electrician we’ve used over the years has been remotely fazed by the idea of dedicated mains and separate consumer unit. It’s your money and if you want it, they should provide it.

Get the separate CU. Ensure that the earth from the hifi CU does directly to the meter. Do not piggy back off the main CU. When we first had dedicated mains, it was installed with a piggy back earth. It was later changed, having read about the benefits on here, and it made a difference at least as great as having the original setup installed.


I’d say there are a couple of things to consider that counters what your Electrician said.

A) As has been written the bigger gauge cable from RCB to wall sockets will reduce resistance. Lowering resistance on the AC is a positive thing. Just like lowering the earth impedance.

B) although we can’t isolate our supply from noise generated by other consumers on our grid we can isolate the noise from the usual culprits in our own properties by fitting a dedicated supply tailed off pre main consumer unit. It’s tried and tested by so many hifi owners.

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Actually this is what an isolating balanced power transformer is for. Many on the forum use them. I had planned on it but lately electricity costs made me think twice so I’m just having a wide loop to the secondary CU so that it is very easy to add one later. For hospitals, isolating transformers are mandatory for circuits with some equipment like NMRIs.

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I meant all things being equal.

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Yeah I know. I didn’t mean to be a pedant. Occupational hazard. I didn’t mean anything by it.


I’m not sure it makes much difference particularly if you live in a built up area. Of course, your hifi will derive some (limited) benefit from not sharing the same CU as other ‘ noisy’ appliances in your house but, unless you have your own generator, the power supply coming in to your property will always be compromised by the other properties demand on that shared supply. So I think your electrician has a pretty logical perspective. That said, loads of folk on here do it and swear by it so you may as well if only to make you feel like you’ve done the right thing. In this game that counts for quite a lot in my experience!

For the extra little bit of hassle, I’d always go the separate CU, David. @Cohen1263 has summarised it nicely.

I had my dedicated supply installed in 2018 and I still think of it as one of the best value (for the price of a Power-Line roughly) things I’ve done. A SQ lift when first installed and the consistency of system performance it brings, regardless of what else is going on in the house. I’d definitely do it again if we moved.


As others have said, using an existing CU/or inserting the hi-fi breaker in one, is regarded as sub-optimal as it exposes the feed to internal contaminants e.g. fridge/freezers, SMPS supplied kit, boiler pumps et al – hence why splitting off via a dedicated CU (fed first from Henley block) is the advocated way to go.

Also ask the sparks to check and clean the incoming mains fuse/even replace it, if it’s elderly.

@feeling_zen Thanks for that great detailed reply.:+1:

A dedicated earth…How does one install that?


In the UK (and I expect other countries), this will need to be done by the qualified sparks — or, at least, he will need to connect it up and check the install.

The reason I say this is that it depends on how your house is wired-up to the incoming mains and the mains earthing set-up. You may have to stay with the mains earthing arrangements – otherwise, your bespoke earthing arrangements might turn out to be the earthing arrangements for the neighbourhood i.e. shortest route to ground.

If he says it’s OK for the hi-fi CU, then it’s normally done by sinking long (~1m) copper earth rods in the garden (ideally, where it should remain damp/doesn’t dry out), running a protected earth cable to these, and back to the CU.

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As above :point_up:.
You’re Electrician will know if you are being supplied with a PME system ( neutral and earth bonded together) or a TT supply which lends itself very well to those of us who want to install a dedicated earth via a series of earth spikes (kept moist).

IME the dedicated earth has provided, on three occasions now, at least as big an improvement to the sound of my system as the dedicated AC supply. Steve Sells recently posted that both Mark Raggett and Roy George have installed them in their homes.

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I would be interested as a rough average how much does / can this work cost ,
Hundreds/ thousands ?
Every instillation of course is different,
Never inquired off of a professional so please excuse my ignorance :thinking:
Seems a lot of people have solved the dreaded toroid hum this way to

I supplied the plug socket, the electrician the cable, CU and Henley block……£120 with tip.

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