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Help with electrics needed


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Hi all

Just had the quote back from my electrician for installing 16 sockets and 2 lamps in my obsy, he has quoted for 16mm 3 core armoured cable, does this see overkill to anyone? I thought iIhad read most people use 4mm.

Any help gratefully received

Cheers Jon

Edited by BeyondVision
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Well, 16 sockets is quite a lot. Are they all going to be fed through one cable?

I'm not exactly up to scratch with cable sizes but 4mm seems a bit thin for 16 sockets.

Are you going to run the cable overground or underground? If underground you might get away with using "normal" cable (not the outdoor armoured variant) and run it inside a hose pipe that has a metal mesh layer. make sure both ends of the hose pipe are indoors and that the hose is in one piece. Not sure if that works out cheaper but might be worth checking.

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I guess it depends on how it's measures... my Armoured cabling is 16mm in diameter.. that's the outer diameter, not the core though...I can't remember what it's rated for in terms of current capacity... quite high I think... and that's going to be the key dependency for that many sockets

Edited by jgs001
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So did I, but 16mm cores would mean an enormous cable...

The armoured cable I had put in, really wasn't cheap... surprisingly expensive on a per m basis. Just had a quick look and 4mm core cable is £2/m from Screwfix Direct.

Edited by jgs001
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What sort of current are you going to be drawing? Lots of sockets doesn't always mean lots of power use.

Could you run it all off 1 or 2 13A extensions? (Obviously with RCDs and suitable weather proof stuff where necessary) That way you don't even need an electrician.

Edit... Crikey lots of responses since I last looked before posting. Hmm, at 70m I think I'd look at ta professional job too.

Edited by haitch
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With 16 sockets you have the potential of drawing 16 x 13A = 208A !!! and over a 70 mtr run it could get a tad warm!

Nope...

It will be fed from a fuse in the consumer unit which will

dictate the maximum current you can draw.

Most main incoming fuses to the house are only 100A:)

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Nope...

It will be fed from a fuse in the consumer unit which will

dictate the maximum current you can draw.

Most main incoming fuses to the house are only 100A:)

I only said the potential to draw that current!

I use a 16amp RCBO in tha fuse box and 2.5mm cable to the obs.

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Hope I can help here a bit. I am a Sparky and do this sort of thing regularly. There are a couple of questions, first is regarding load. When you say 16 sockets, is that 16 double sockets or sixteen places to plug in something. The regs regards a double socket as one outlet. So what some people would commonly call sixteen sockets could be actually 8 double socket outlets. Still, its quite a few. If its for an obsy, I can't imagine you,re running anything huge except maybe a 2KW heater for those winter nights. It's a mistake to add up each socket as a 13 amp load. The regs allow for diversity which means that they know that not every outlet will be pulling maximum power all the time. You can see this in your house wiring because your ring circuit will likely be protected by a 32A breaker but you probably have 10 or more 13A outlets on that circuit.

The second point is that you state the cable run is 70m. The most limiting factor in cable selection is not load capacity but volt drop. The regs has a minimum permissible vold drop from the source (your fuse box) to the point of utilisation (the socket or whatever). This is 3% for lighting and 5% for all other applications. So if you plan to have lighting on your new circuit, the maximum volt drop must be 6.9v based on a 230 supply. On a long run this is probably where the 16mm figure has been calculated. The longer the run, the bigger the cable needed to me the volt drop requirements. So you are probably not being ripped off by the sounds of things. Your contractor seems to know what he's at in this case.

Sorry to go on a bit, I get carried away. Hope this helps clarify the situation. BTW it needs to be RCD protected. Armoured cable is not essential if its not buried but it will need to be in a conduit if not so its probably the neatest solution. It is the way I would recommend.

Cheers

Richard

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