Configuring radial sockets for audio use

[AlexM]

Hi,

I am in the process of some electrical re-working of my installation in preparation for a move of my system to a new location in the room.

I have installed a new Memera consumer unit, and have made allowances for four radial circuits on individual MCBs. Wiring between the consumer unit and the sockets is via some very heavy twin and earth cable (10mm). Each radial circuit will be terminated as a double or single 3-pin switched outlet.

My question is how should i connect my equipment to minimize the chances of an earth loop, causing hum. As the cable runs to the consumer unit will be short and the earth connections within the consumer unit will share a bus bar, any difference in earth resistance should be very low and maybe there won't be an issue, but I have suffered from ground loops in the past and am very keen to avoid this with the new installation.

So.. this leaves me with a couple of questions..

1) How to best arrange power leads and sockets to minimize ground loops. As an example, should my sources and the preamp be plugged into a double socket together, or the preamp and the power amp etc, power amp into a single etc.

2) How to reduce noise injection into the mains by unavoidable switched mode PSUs - separate them onto their own radial circuit? All are class 2 devices with no earth connection.

3) Anything else I should be considering?.

Thanks in advance for any advice or input.

Alex

[AlexM]

And while we are at it, what about choice of sockets? Brands? switched vs. un-switched?. Not really intending to spend a fortune so just looking for top quality stuff readily available from electrical factors (MK, Crabtree, Others), and needs to have a white external finish.

Thanks in advance..

[Reid Malenfant]

Let me see if i have what you are intending to do straight in my head ;)

You are planning on running a 10mm^2 twin & earth cable from the new consumer unit to each socket? Have you tried physically fitting the 10mm^2 cable into the connections? I reckon you might be lucky with 6mm^2 as they are designed to take 2 x 2.5mm^2 in a standard ring.

Anyway, getting away from that for a bit. Why don't you just connect one earth to one set of sockets & from there connect to all the other earth pins in the others? That way you shorten the loop & it should still be perfectly safe. After all it'll be at earth potential ;) Look around anywhere these days & you'll see earth bonding onto water pipes, so i see no difficulty with safety doing this. Well that is as long as you aren't going to be pulling 10KW from the mains at any rate :eyebrows:

I'd suggest you plug stuff with SMPS into a seperate socket & use some kind of mains filter like a Belkin PF40 or similar to prevent too much garbage getting back into the mains. You see the chances of all the SMPS switching at the same frequency is more than winning the lottery, so all sorts of random noise will get back into the mains. In the case of the Belkin PF40 you can connect them into different filtered sections which will help even more imo.

I think i'd go for switched sockets. Because you'll be feeding everything with such an incredibly low resistance cable i honestly don't think you'd notice a switch inline with the kit. Besides which i like the idea of being able to switch stuff off rather than have to unplug everything for safetys sake.

Hope that helps :)

[AlexM]

Mark,

Thanks for the input and suggestions. Upon checking, the radial circuits have been wired in 6mm twin and earth, not 10mm as I originally said. My electrician has said that this should be usable with a standard socket - 10mm definitely wouldn't be!.

I will ask my electrician regarding strapping the earth connections together - shouldn't be a problem from a safety POV, but just curious as to whether there would be any effect on the operation of the MCBs. I'm looking forward to seeing if this improves matters compared to running everything from a single socket on the ground floor ring main.. I'll keep you posted!.

Thanks,
Alex

[Reid Malenfant]

MCBs only operate on a current overload, nothing to do with Earth fault currents. For that you need RCDs or Residual Current Devices which sense a difference between current on the Live & Neutral line.

If there is a difference between the two of more than 30 or 100 milliamps (depending on the type) the only place it can be going to is Earth so they open the circuit :)

Yes, 6mm^2 seems more sensible, but it's still a lovely low impedance cable :eyebrows:

[AlexM]

Hi,

I stuck my head round the door to ask the sparkies how they had configured the radials and they explained how they have installed them, which is not quite as I had expected..

The consumer unit has a split bus bar, each protected by an RCD. Two of the radial circuits are on one bus bar, two on the other. Each radial has an individual 16A MCB (I think).

I think that it turned out that way as there were too many circuits to fit the house services onto one, and audio stuff on the other so they are split between the two.. oh well.

At least there are only three connections between the sockets and the meter tails and the total distance is about five meters. I guess that the earth potential and resistance is going to be virtually identical, so hum loops shouldn't be an issue. I guess if the earths were all strapped together a fault would trip all of the circuits, which wouldn't be ideal.

So perhaps the best final connection scheme is put switched mode PSU stuff on the radials on one bus bar, and amps and source components on the other. Perhaps it doesn't really matter and I should stop worrying about it!.

What do you think?

Regards,
Alex

[Reid Malenfant]

If they are MCBs then i'd hazard a guess & say that only the main breaker would trip, as this should be an RCD of some description. I'll be honest though & state i still have a fusebox :eyebrows:

Yes, i'd go along with your idea of only putting stuff with SMPS on the one bussbar, try to filter it to so as you get the least main noise back into the system. A seperate filter for all you more conventionally powered components is also a good idea, depending on this filter it might be best to plug any power amps directly into the mains though ;)