Dedicated mains - Survey

This is a non scientific survey about dedicated mains.

To elicit facts, not opinions, please.

Please answer these Qs:

  1. Age and condition of the existing wiring
  2. Separate CU and what make
  3. Cable SA mm^2, and make/type
  4. How many sockets of what type
  5. Effect on SQ, e.g. worse, no change, slightly better, loads better, specific effects.


(If you’ve done this more than once please report different instances).

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I rewired my cottage in 2012, specifying a dedicated mains. Normal cabling was used and the CU and switchless plugs were all standard Crabtree. I had a dedicated cable / radials to 5 locations: each with double sockets.

In 2015 I upgraded this setup by adding a new earth wire to the main hifi location and added two more sockets. This time one of the Crabtree CU was replaced by two Eaton boxes.

Each instance improved SQ significantly.

0- whole house re-wire in 2004
1- MEM CUs x 2 - obviously one for hi-fi, fed via 1st splitter from supply
2- 10mm ‘cooker cable’ - make cannot remember - bugger to work with and de-sheath!
3- 6 radials with enhanced earthing (no more can be said).
4- better - very much yes

Of course, all works done by qualified sparks.

But there are suggestions one 10mm radial with a very good quality star-wired distribution block is a better way to go – but latter is actually more expensive (vis relative cost of block) it seems and I’ve not yet read 100% confirmation around star wiring of internals, with suggestions of rings etc.

0 - Rewired 2003
1 - Memera 2000ad consumer with 100A 30mA main switch
2 - 10mm twin and earth
3 - 6x 32A equal length radial circuits with enhanced star wired earthing
4 - Huge lift in sound quality

Its so long ago when I had a dedicated main spur direct from the cusumer unit in the garage and under the floor next to all the kit I forget the date. Its when Studio 99 in Swiss Cottage were active.
30 or 40 AMP wiring, quality wall sockets and unswitched. If you were OCD you could take the socket heads off and tighten the screws. Some WILL be loose I bet.
Yes: well worth it. Reduced transformer hum as well.

0 - 1.5 years
1 - Separate Hager CU
2 - CSA 10^2 armored cable, of no particular brand
3 - 2 x (2 unswitched sockets) MK Electric Logic Plus, each with a run of 10^2 cable
4 - can’t compare as had this setup from the start

  • Existing 29Years, new HiFi radial <1 year
  • Separate CU 4-Way MK 100Amp Metal Consumer Unit (Y5704sMET) with C curve 32Amp 6kA 30mA RCBO
  • SWA 10mm single run
  • 1 double unswitched MK Logic Plus
  • Had a cold at the time, so never got that immediate improvement, also did a couple of other upgrades at the time, so can’t say, but Humming did decrease a little.

Please answer these Qs:

  1. Dedicated spur, installed 4 about years ago
  2. No CU - only a Siemens Sitor cylindrical fuse holder 32A - no regular MCB
  3. Kemp Electronics 5 x 1,5mm2 shielded - connected in pairs (thus 3mm2 + 1,5mm2 earth)
  4. Spur directly connected to Puritan power strip, 6 sockets
  5. Very clear and fundamental improvement of all aspects of SQ (the audiophile lingo book)

ADD: I had an earth rod installed under the house (16 meters deep) providing clean and low resistance earth, only for the spur. The improvement in SQ was at least as much as the dedicated spur, if not more.

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When I had the plaster off to redo the damp course I tried to get an electrician to put in a dedicated radial but couldn’t convince the little jobsworth to do it. The plasterer was booked so I put my own 10sqmm wire in and sank a very deep backing box into the wall leaving the feed end unconnected. I then had the work certified by another electrician when he redid the lighting circuits, checked the power circuits and fitted a new consumer unit, connecting my cable to it’s own breaker but not a separate consumer unit. He criticised that I’d not put a sleeve on the earth wire in the backing box but was OK with the rest of my effort. I’d moved a doorway and turned the room 180 degrees from where it was before so a direct comparison wasn’t made but the whole exercise was a success. I used a double unswitched MK socket and ran a home made block from it, the block having single MK unswitched sockets wired in a chain.
I’ve just sold that house but have been living in a flat for the last year and a half with no dedicated mains. Going from a room 4.1m by 3.8m to one of 7m by 6m has been more beneficial than the rewiring, I’m still using my home made block.

  1. 2010 barn conversion, so new wiring direct from HT network cables via transformer then underground to external electrical kiosk. No neighbours for at least half a mile.

  2. MK CU with 40amp fuse

  3. Dedicated radial spur using 6mm2 Amour core cable

  4. Three MK un-switched double sockets with star earth arrangement. Also use several external grounding rods in a star formation at the other end.

  5. Immediate improvement in SQ compared to the house ring-main. A surprisingly bigger jump when I added and rearranged the earthing rods into a star formation. Sound is very dynamic and natural. Less harsh than the house ring-main. Overall better than any black box I’ve ever added.

Surely Q4 is inviting an opinion?

Thank you to everyone who has posted so far.

Some very interesting details for anyone who is thinking of doing this (as I am when I finally manage to move house).

Please keep the reports coming - including ones where little or no improvement is gained (of which I’ve seen 3 reports recently on the forum).

One thing I probably did not explain well is about the first Q.

I was hoping people would mention how old the wiring was that they replaced when they added their HiFi radial (or ring).

This is because I wonder whether most of the SQ upgrade is:
A. Because fresh wiring replaces (very) old wiring that is sub-standard/loose/rusted, etc?
B. Because it’s thick cable (e.g. 10mm)?
C. Because it’s off the house main ring and therefore brings less EM noise into the HiFi?
D. Because of the improved earthing arrangements (where these were improved)?
E. Other.

Just to complicate things further, I always wonder how much effect the typical UK ring mains design has vs. other countries, and also the effect of a detached house vs. apartment building.

Because, e.g., in Germany we don’t have ring mains. There’s usually a fuse box in the apartment/house with a separately fused circuit for a bunch of consumers. And, at least in not very old buildings, there are many. In my apartment, there are 26 fuses in the apartment’s box for 26 separate circuits within the apartment. The kitchen appliances like dish washer and fridge are on one, the kitchen wall plugs on another, and yet another for kitchen lights. The washing machine has its own one, same for other special consumers. Each room has more than one circuit for various wall plugs, and another separate one for ceiling lights. And so on, you get the idea.

In my case, it turned out that the 4 wall plugs that were meant for the media location (where the cable TV and internet outlets are as well) are wired up to two separate circuits. So I just plugged the hifi into it’s own one.

Each of these circuits has a separate wire back to the apartment’s fuse box.

However, upstream from the fuse box these separately fused circuits are of course all connected to the same mains supply that goes into the apartment. And this apartment supply, together with the other 100 apartments in the building, is obviously connected to the building’s common supply somewhere in the basement.

Electricity being what it is, my guess is that there is zero isolation between my hifi’s plug from the rest of the building, separate circuit or not.
Probably my building, together with all the other buildings in the neighborhood, are eventually linked together in one huge electrical circuit that extends to at least the transformer that supplies the whole neighborhood, probably even farther.

  1. Age and condition of the existing wiring
    House is 50 years old, hi fi spur originally about 15 years old but re-routed 2 years ago
  2. Separate CU and what make
    No, through 2 year old shared MK distribution board (kitchen was rewired hence new board). 32A type C RCBO
  3. Cable SA mm^2, and make/type
    6mm inc 6mm earth cheap stuff
  4. How many sockets of what type
    splits in last few inches to 2 banks of MK unswitched twin sockets with another 2 banks radially to these, although now only use 1 socket on each double
  5. Effect on SQ, e.g. worse, no change, slightly better, loads better, specific effects.
    Undoubtedly better, all aspects of music clearer. About a black box worth I’d say

Previously I had an earth rod but after reading about the potential of any local fault in the area being routed through your house as the transformers at the sub are often not earthed, I decided to go for the seperate radial.

I wouldn’t get lost in evaluating against age et al. The fact is that getting a dedicated supply gets the feed away from mains contaminating kit (e.g. freezers and fridges), so it can only be better. And if someone has elderly wiring, there’s really only one option and that’s a 100% re-wire – bearing in mind that modern houses will have/probably need more sockets than older installations. My understanding is that re-wiring is required every ~35/40 years now.

The days of just putting a new CU in and connecting up to old have gone IME - a decent sparks has to check all circuits in any event and if they find something which isn’t ‘right’, many will only re-do by starting afresh, as they have to warrant/certify their works and don’t like doing this when they cannot see/perhaps examine all ‘existing’. It can often be cheaper to start afresh too.

So if the house I move into is 6 years old, it’s still worth it for the isolation from mains ring and the fat cable?

I would say yes. And it shouldn’t be that hard to do - obviously dependent upon locations & positioning, and methods of construction.

A dedicated CU (split fed from supply via Henley block) and feed(s) would be better than a feed from one of the gangs on the existing CU/off a ring (e.g. the downstairs sockets ring exc. kitchen). Earthing to be addressed as needs be with sparks.

Many around here regard as the cheapest upgrade (in relative terms!).

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I’ve had a dedicated supply installed 3 times in the last 8 years in 3 different properties. Prior 2 were 6mm2 wired from CU. The latest one has 10mm2 from main box to a seperate CU which is in the room next door to the listening room and positioned directly behind the hifi equipment from which I run 6mm2 through the wall to twin double, unswitched MK sockets.
All installations have had similar MK unswitched plastic sockets.

There’s been a definite improvement in all 3 instances over the standard house mains. TBH, I’m not sure I’ve heard the night and day improvements that some others report, but a clearly more relaxed and together sound with better separation of musical strands. Very worthwhile.

The one disappointment in all 3 cases is that transformer hum has never been improved by the dedicated supplies which I guess just shows that the cause of the hum has always been present on the mains supply before it even entered the house(s).

Similarly unless the house has more than one phase supply, or an isolating transformer on part, both of which are rare, there is zero electrical isolation as such between any of the outlets on a British ring main and a separate radial circuit supplied from its own consumer unit (fusebox), except when one is switched off or a fuse has blown or circuit breaker has tripped. And the same applies regarding buildings linked externally on the same phase back to a transformer somewhere in tge distribution system.

Any effect of a separated local supply for the hifi system as normally described can only be due to differences arising from current carried on the home part of the cabling, or by injected interference (e.g. RF noise) being ‘diluted’ by the path it would have to follow compared to if arising on something connected to the same final circuit.


In case people are interested, and didn’t know this, the Ring Main came about post WW2 and was developed due to using less copper, which was a scarce metal at that time. Quite ingenious really, and a lot easier to manage 2.5mm2 cable rather than 4

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