Planning a dedicated mains circuit - questions

[newtonnjd]

Hi All,

I am just about to take the plunge to get some dedicated mains power to my audio room. I've done several hours of reading on this forum and would be grateful for some help choosing the best way to proceed.

So the background info. I'm in the UK. I have an extension which I used as a dedicated home cinema. The main distribution board was installed about 8 years ago and has 2 spare breakers. Luckily one of my best friends is an electrician, and is very familiar with my set up (we do movies every friday!). So all the tricky/dangerous bits will be in safe hands, and won't cost me anything

My ideal path for the new wiring is getting it outside and along the external walls of the extension, coming in at the back corner of the extension, as I want to avoid as much destruction inside the house as possible. This will require 19m runs of wire.

My initial thought was 2 separate radials using the 2 spare breakers, one radial for the power amps, one for the sources and pre amps.

But on reading threads here I'm not sure anymore!


Firstly, my electrician friend is suspicious of audiophiles and thinks 4mm mains cable will be just as good sonically as 6mm or 10mm. My reading here indicates that 10mm is commonly used. Can I give him a solid explanation of why bigger is better?

Secondly, opinions on my options:

A. Single radial + mains block
B. Two radials, amps plugged directly into wall sockets of one, mains block for other equipment on the other
C. Single heavy duty wiring out to a separate distribution board in the audio room feeding multiple single unswitched sockets

If going with my original idea of two radials, does running the 2 cables side by side for 19m cause any problems?

What type and thickness of cable?

My budget for wiring, sockets etc is ideally £200-300. If I'm going to do it, I'm happy to spend a bit extra for mid range products, but can't afford top end stuff.

Thanks,
Nick.

[Barry]

Well you could chat about the reduced source impedance achieved using thicker cables, though unless you know what the value is already the question is moot, and I doubt your electrician friend would be convinced.

Or you could talk about the lower voltage drop through using thicker cables. As far as I know the maximum permitted voltage drop for a cable run is 5%, say 11.5V for a maximum current of 16A. So cable resistance of 0.72 Ohm for a 19m run, ought to decide the gauge of cable you need to use.

Out of your choices I would go for option B: two runs using the two spare circuit breakers in your CU. You now have the choice of what style of plug and socket to use. Since you have a 16A rated breaker in the CU, you could use 15A round pin plugs and sockets, or you could use conventional 13A plugs and sockets.

The best option IMO would be a variant of option C; that is to fit a 32A RCB alongside the CU with the tails of the former going direct to the meter (via a Henley block if necessary). Then run a 32A rated armoured cable out to your extension and thence to a separate CU, which in turn feeds the sockets. If you are feeling extravagent you could have each socket protected by its own breaker in the new CU. Again you have the same choice in which plugs and sockets to use.

The above is similar to what I have had done recently.

[newtonnjd]

Barry,

Thanks so much for your thoughts.

I have to say I have no idea how to do the cable gauge calculation based on those numbers, but hopefully it will make sense to my friend!

So to confirm, if I went for two radials, there'd be no issue running them side by side over that distance?

I think your variant of C is actually what I was trying to describe, but I left it vague as I'm still not that comfortable with all the technical terms!

I do like the sound of the 15A round pin plugs. Though just a week ago I foolishly ordered an expensive power cord with a 13A plug.

I am thinking of building my own box to house my sockets of choice. I work best with wood, and I'm picturing a wooden box about the same size as a typical CD player, with multiple single unswitched sockets mounted on the top surface, fed underneath by either the two radials or the new CU. Does this sound sensible?

If I don't go for 15A round pin, I like the look of the missing link silver plated sockets - EPS 50. But then I've seen some people really praising the use of schuko plugs and sockets. I guess if I went the round pin or schuko route with no fuses in the plugs, I would need a single fuse somewhere in my wooden box protecting all the sockets?

Thanks,
Nick.

[Ali Tait]

The fuses in the plugs only protect the cable that the plug is on the end of. The circuit breakers in your new CU and the ones in your existing CU will protect the circuit.

As for cable size, use the largest you are happy paying for. If you are running along the outside walls, you will need to use steel wire armoured cable, but your sparky mate will know this.

[newtonnjd]

Thanks Ali.

I assumed I'd still need a fuse before any new fuseless plugs/sockets, based on comments by Marco about using a schuko mains block and schuko plugs, but still having a fuse in the 13A power lead connecting the schuko mains block to the wall..?

[Barry]

If you go for option C and have a dedicated CU in your extension, then if each socket has it own 16A breaker in the CU, you can use either Schuko or 15A round pin sockets.

[Ali Tait]

No, round pin or Schuko plugs don't have fuses, as I said, the breakers in the new and existing CU, and the fuses in your equipment all protect the wiring.

[Barry]

To answer your query about cable gauge, have a look at this: http://www.csecables.com/power-cable...d-power-cable/

IMO, if you are going to go for option B and have two cable runs, then 2.5mm² cable will be fine (50A rating). If option C, then either 6mm² (80A rating), or 10mm² (100A rating). As Ali says, go for the largest you can afford.

[newtonnjd]

Thanks both. I do understand what you're saying about the breakers negating the need for fused sockets. I just don't understand why Marco put such emphasis on a mains block with schuko sockets still having a single 13A fuse in its own lead - why would he not have said that this single fuse was also unnecessary? I can try to find one of his posts about it if that will help.

Thank you for the link showing cable choices. So you would recommend buying my chosen cable from there? If it's about what I can afford, then even the 16mm is easily affordable on that site. For a single run out to a separate CU, would I need 4 core wire, or is 3 core enough?

[Ali Tait]

He probably uses a normal plug on the power lead feeding the mains block.