Dedicated Mains - Some Pictures
Posted by: DaveBk on 21 February 2009
In recent months there has been quite alot of interest in dedicated hifi mains circuits. Many people have asked what is involved so I thought I would post a few pictures to explain what I have done:
This shows the new hifi consumer unit. It's fed directly from the incoming mains using 25mm power conductors and a 16mm earth. Two 32 Amp circuit breakers feed the 6mm and 10mm radials.
This shows the 2 radial circuits crossing the loft before heading down the wall buried in the plaster.
And this shows the final socket outlets on the wall. The switched one is a spur off the upstairs ring that is used for the Sky box and DVD player. Next is an unswitched double where the 6mm radial terminates - this powers the NAP300 in my case. Next to this is the 10mm radial again terminated with a MK unswitched socket powering the Supercap for the NAC252 and the Transporter. The Transporter is modified to replace its switched power supply for the digital side with a linear unit of my own design so no nasty RF gets back onto the radial.
Finally an picture showing one of the measurable benefits of dedicated radials. The meter is an earth loop tester - it measures the resistance of the whole circuit from the local substation to the socket via the live and back to the earth. (Earth and Neutral are usually joined in the cut-out where the mains enters your house) Generally speaking the lower the resistance the better. The meters are shown in the same order as the sockets so it can be seen that the 10mm radial has the lowest earth resistance - low resistance return paths to earth are important in my experiance with high end hifi.
The only place in my setup where the mains earth is connected to signal earth in in the Transporter, this should be connected to the 'stiffest' earth so I use the 10mm radial. I also power the Supercap from here to keep it away from the 300PS.
So this wraps it up, not forgetting of course the 3 Powerlines from the sockets to the kit.
Posted on: 06 March 2009 by Consciousmess
Thanks for that information, Dave.
I have to say that I have just had another electrician round to give me another quote, for which I am expecting tomorrow. I'll then get the job done next week.
I do need to ask another question though, and thanks in advance for helping, but I have specified to both electricians that I want to have a 10mm spur and the one today said he's not sure whether that would fit in a socket.
I told him that I have been advised to go for a 10mm spur and it has to be this. I don't want any corners cut you see.
But can I ask did you have no problems fitting a 10mm cable into your double wall socket?
Many thanks,
Jon
Posted on: 06 March 2009 by DaveBk
I used MK Logic Plus sockets which could take 10mm cable. Remember that 10mm squared is the cross sectional area of the cable, the diameter of the conductor is only about 4mm so should fit. 10mm cable is quite hard to bend so I fitted deep pattress boxes to give me room to maneuver.
Posted on: 06 March 2009 by count.d
quote:
MK Logic Plus sockets which could take 10mm cable
The Mk sockets sold within the last couple of years are crap. They have plated steel terminals and earth bar.
Sometimes reputation isn't everything.
Posted on: 06 March 2009 by DaveBk
I'll take another look at them - I remember thinking that the Logic Plus range had brass terminals.
Posted on: 07 March 2009 by Consciousmess
Thanks for that, points noted. Count D., on reading your post, what did you use instead of Logic Plus?
Regards,
Jon
Posted on: 08 March 2009 by count.d
Jon, I used Crabtree. These need to be checked for any loose riveted connections before the electrician fits them.
However, I may be onto to something good shortly. I constantly look for better sockets and I'm excitingly awaiting delivery of a sample for me to check. If it's good, I'll be changing mine.
I would consider mounting the sockets a metre or so high on the wall, so that the cables aren't lying all over the floor. This will make cable dressing so much better.
Posted on: 08 March 2009 by 555
At the moment I use MK switchless sockets.
I asked my sparky to get me Crabtree SS to try, but he hasn't done this yet.
Please let us know your conclusions count.d.
Posted on: 08 March 2009 by Stuart M
I had a separate consumer unit with RCB's fitted going to 4x2 13 amp (switched) sockets and another to a distribution box where I connected a hydra. This worked brilliantly and was done before the requirement for circuits to be "Locally isolatable". This involved my electrician carpenter running 5 cables (10mm) through to my listening room.
What I wish I'd done (and it would comply with todays regulations) AND have been cheaper would have been to run an armored cable through to the listening room, put the HiFi consumer unit there and then distribute from that with unswitched sockets. This would make them all locally isolatable(via the consumer unit) (required by current regs), all with RCD's (required by regs), a minimum of switches involved and reduce cabling costs.
I was away when this was done (my builder thought I was mad) so he made the electrician do what I asked for (including cable direction) but when I meet the electrician he told me a better way to conform with future regulations AND reduce the number of switched in the path.
(Note Adam - tried to msg you on this to notify you if you wanted to check this as this is a legally v sensitive subject but could not find how to PM you)
Posted on: 09 March 2009 by DaveBk
Great idea - it had not occured to me to run armoured cable through to the listening room. I would have had a tough job convincing Mrs B about the consumer unit in the current room, but if I ever get to build the dedicated listening room extension I aspire to this would certainly be ideal.
Posted on: 14 March 2009 by count.d
quote:
Originally posted by 555:
At the moment I use MK switchless sockets.
I asked my sparky to get me Crabtree SS to try, but he hasn't done this yet.
Please let us know your conclusions count.d.
555, excitement about my new socket find didn't last. A free sample arrived, but it was not to the spec that I read on the pdf.
On top of that, conductivity of metals is a complex subject. I was surprised to find that phosphor bronze is a fairly poor conductor even though it's 90%+ copper.
I need to get out more.
Posted on: 14 March 2009 by 555
Me too count.d!
Thanks for letting us know.
At the moment do you use Crabtree sockets?
I'm trying to decide if it's worth changing my MK.
Posted on: 15 March 2009 by count.d
555, I use Crabtree sockets which are the 2 years old design. They seem ok, but not exactly perfectly made. I can't help but cringe when I see the construction quality of sockets.
I have a couple of ideas to improve sockets, but it will take me a long time, as I don't want to do anything illegal or compromise safety.
Posted on: 16 March 2009 by 555
Thanks for that count.d.
Posted on: 16 March 2009 by DaveBk
quote:
The Mk sockets sold within the last couple of years are crap. They have plated steel terminals and earth bar.
In response to count.d's quote above, I finally got round to looking at a spare MK Logic Plus socket I had in the garage to see just how crap they are, or are not as the case may be...
From the outside the socket appears well engineered, but it does have a steel earth bar as count.d mentions.
Taking a look inside, the internal busbars are solid copper and reasonably thick. All the plastic parts are very well moulded.
A better look at the live and neutral busbars.
This is the earth busbar which is indeed plated steel, but with riveted copper socket contacts. As this is the only 'suspect' component found, I measured its resistance using a Megger inculation/conductivity tester which can read down to 0.01 Ohm - over the longest distance end to end it was less than 0.01 Ohm - reading was 0.00. So the actial resistance between the contact and the cable terminal is virtually zero. I'd need a good milliohm meter to even read it.
Turning to the screw connectors they are also plated steel, but this is actually quite clever engineering - the copper busbar is inserted through the steel connector so that when the screw is tightened, the copper wire is pressed hard against the copper busbar. As the screw and connector are steel, they can be done up much tighter than traditional brass contacts so could well make a better connection in practice.
Overall, I think MK have done a good job here and I'm happy to continue using them on my system. Hopefully these pictures are OK Adam? The socket was obviously destroyed so no chance of it breaking any regs!
Posted on: 16 March 2009 by BigH47
Now that's dedication, a full destructive test. Well done. I thought they seemed OK while I was constructing a 3 x twin star earthed with female IEC socket extension lead thingy.
Posted on: 16 March 2009 by count.d
Dave, I genuinely don't understand your claim that the Mk sockets are not "that crap". You've dismantled one and boldly posted pics that just illustrate what I stated.
The recent sockets, like yours, are crap.
They've changed the earth bus bar from solid copper to plated steel and so the direct connection to the bare wire is a plated steel insertion. Disaster.
They've changed the solid brass terminals to steel plated. The best connection for the wire now is, only one sided, to the copper insertion - the remaining 50%? through plated steel. The argument for steel connections allowing more grip is nonsense, as tightening beyond a certain force will only crush the copper wire and can actually cut through individual strands. 25%? of the connection is through a steel plated screw.
Regarding the resistance, I think you need to do a little more research. You'll have to measure with more accuracy than to 0.01 ohm. One hundredth of an ohm over a relatively short distance is huge.
Finally, silver is a better conductor than copper, but it sounds awful. Go figure! (my God, I got to use the Naim phrase proper).
Posted on: 16 March 2009 by BigH47
quote:
They've changed the earth bus bar from solid copper to plated steel and so the direct connection to the bare wire is a plated steel insertion. Disaster.
This is the use of disaster as in 500,000 tonnes of oil on a beach? Or in the, it sounds a weeny weeny bit better with the old sockets?
Posted on: 16 March 2009 by count.d
Point taken BigH. Going to bed now.
Posted on: 17 March 2009 by 555
Posted on: 17 March 2009 by DaveBk
count.d - I guess we'll just have to agree to disagree... until the day that Naim use their powerline experience to make a wall socket that is
Posted on: 17 March 2009 by count.d
quote:
Originally posted by DaveBk:
count.d - I guess we'll just have to agree to disagree... until the day that Naim use their powerline experience to make a wall socket that is
Agree to disagree about what?
Dave, you obviously still don't know what I'm saying.
Within the last couple of years and compared to...?
You know best.
Posted on: 18 March 2009 by DaveBk
count.d - my point was simply that I do not believe the MK sockets I use are that bad compared to many of the genuinely crap generic own brand units that I've come across over the years. I wish that someone would make a genuine high-end socket, all copper busbars, welded connections, brass terminals etc, but until that day we have to make compromises. In my case, I'm happy to accept a less than ideal earth busbar material as to my mind it still gives me a sufficiently low impedence earth connection. I base this on the fact I've got 16m of cable in my radial, the earth conductor being 4mm. At 4.61milliohms/m this contributes a little over 0.07ohms where the 30mm of steel in the socket adds <0.01ohms.
I think the point we disagree over is the definition of 'crap' that's all.
Posted on: 18 March 2009 by count.d
quote:
In my case, I'm happy to accept a less than ideal earth busbar material as to my mind it still gives me a sufficiently low impedence earth connection.
You're also happy to argue with me.
Are you happy with the MK series connection for the L&N?
Posted on: 18 March 2009 by DaveBk
I see it as more of a discussion than an argument... with regards to the L&N, yes also happy. I understand your point over only half of this being a true copper to copper contact, but the alternative is usually a brass to copper rivet which imo is more likely to fail or degrade over time. I think I read in an earlier post of yours that checking the rivets is part of your recommendations?
Posted on: 03 April 2009 by Consciousmess
I'll say it again, I'm glad of this thread as it inspired me to get my own separate spur fitted, which I'm about to try later.
What I noticed, however, is the electrician - who has now gone has fitted my separate spur to the original spur that already existed for the other parts of the house e.g. light fuse, upstairs fuse, downstairs fuse.
Is this right? Should he have connected the spur directly to the meter instead??
Many thanks for your help, and I'll post my pictures this weekend.
Regards,
Jon
