[The_Moog]

I'm going to build a workshop down the end of the garden and I need to power it, it's around 100metres from the house.

I need to know about the size of cable needed and how its best layed, my current plan is to stick a flexible conduit in a 2 foot trench then pull the cable through with a rope.

I will be running probably 3x600w lights plus fans and heaters, then i would also like to run (not all at once) a lathe, bench drill, compressor, small welder, lights, radio and kettle that kinda stuff.

So any advice welcomed I was thinking of running a 2 core 10mm2 swa.

[rixy]

The_Moog, on 07 April 2012 - 03:34 PM, said:

I'm going to build a workshop down the end of the garden and I need to power it, it's around 100metres from the house.

I need to know about the size of cable needed and how its best layed, my current plan is to stick a flexible conduit in a 2 foot trench then pull the cable through with a rope.

I will be running probably 3x600w lights plus fans and heaters, then i would also like to run (not all at once) a lathe, bench drill, compressor, small welder, lights, radio and kettle that kinda stuff.

So any advice welcomed I was thinking of running a 2 core 10mm2 swa.

I reckon you'd need 6mm cable for that mate. i wouldn't bother with conduit, just get armoured cable and slap it in. But if you are doing it proper, then be aware of the regs which have criteria regards who is allowed to lay it, and how you run it and mark it up etc.

Best of luck!

[Davey Jones]

50A breaker if you can get one to fit your existing board

I would use a 16mm SWA as its 100 metres and get a 3 core, internal earth and all that, it sounds like you know what your doing though so good luck

Quote

I reckon you'd need 6mm cable

6mm is only good up to 30 amps (ish) and then thats for relatively short runs which means its 10mm minimum 16mm is a better job

This post has been edited by Davey Jones: 07 April 2012 - 05:23 PM

[The_Moog]

Thanks for the advice both of you.

Ill probably go for the 16mm in that case, not cheap though. I must admit to being a bit unsure about the earth, Ive only ever seen the swa used as the earth but those were short 10-15 metre runs.

[Davey Jones]

The_Moog, on 07 April 2012 - 06:07 PM, said:

I must admit to being a bit unsure about the earth, Ive only ever seen the swa used as the earth but those were short 10-15 metre runs.

The armouring is perfectly adequate as the earth (up to very large cables) but IMO a separate earth is better especially for a DIY job but it is more expensive so its entirely up to you both ways are fine

If cost is an issue then its best to work out exactly what load you will draw and then you can install the minimum breaker and cable for your requirements

This post has been edited by Davey Jones: 07 April 2012 - 08:20 PM

[Protein]

If it's 100m you need to take voltage drop into account. The further the power needs to travel, the larger circumference of the cable needs to be to retain the desired power. Depends what kind of load is on the main board it's being fed from. Quick calculation for you based on a 100m run with a 10kw requirement.

Required Cable Size 16 mm
Voltage Drop 10.9 Volts.
Percentage Drop 4.7%
Current Load 43.0 Amps
Max Cable Load* 46.7 Amps

If your main fuse board is bs 3036 (rewirables) it's gonna be difficult to get a 50-63 amp fuse wire for this. Bare in mine that outside power requires rcd protection. I'd make sure that your fuse board is current with 17th edition. I charge £250-350 for fuse board renews just to give you an idea of what to expect. They may insist the bonding to the water/gas meters be upgraded also, so this might push up the price. If you have a modern fuse board with rcd protection bs 60898 (modern switch fuses) fuses in the 50-63 amp range are easy to pick up. You'd obviously need to fit another comsumer unit in the workshop. This should also have rcd protection to help with any problems tripping the main board in the house.

[Themadhippy]

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I'd make sure that your fuse board is current with 17th edition

Why?theres no requirment in the 17Th to bring existingg installations up to standard ,just note it in the inspection and test ticket.As for earthing i wouldnt run an earth ,instead id put a local earth rod in,making it a TT supply,that way you dont have to worry about extending the equipotential zone,and the rules covering TN-C-S systems.

[Protein]

Because all cabling inside walls if not at the required depth need rcd protection as well as 32amp sockets being used by unskilled persons ( i.e the general public ) need rcd protection. You could terminate the swa on a ip adaptable box on the outside of the house, but you are still bringing the cores into the house that wouldn't comply to 17th. Really if someone can afford to buy that much swa and new rewire of a workshop, they won't be grumbling about an extra £250 to make the rest of the house safe too. It's just good practice to make sure any installation is up to standard. And personally I fail any installation I do a PIR on if the fuse board is not up to 17th, i.e no rcd for special locations and socket outlets. I don't need the work bad enough or want the risk of any potential risk to person/property to do work on properties that have old shitty boards. In this scenario I wouldn't do the work unless the main fuse board was upgraded too. I know there are plenty out there that would though.

[PeterGriffin]

yep, armoured cable. don't waste money on 3 core, just get two core and batter in a copper earth peg beside new workshop. no point dragging a 100 metre earth to a different bit of earth...

[Protein]

You wouldnt have too. The combined csa of the mechanical support twisted wires is sufficient. That's what tns systems are anyway basically. It's personal choice really. Ask 10 sparks the same question and get 10 different answers hehe. Comes down to cost really.

[Themadhippy]

Quote

Comes down to cost really.

no it dosnt,it comes down to the incoming supply arrangments

[The_Moog]

this might give you all some idea of the situation with the supply the big fuse says 60A on it. I'm getting someone in to do a full rewire so I'm going to ask them to put in a seperate consumer unit to take the supplies to the 3 outbuildings.

[Themadhippy]

Quote

I'm getting someone in to do a full rewire

in this case id say its definatley needed.On any of the lables does it mention pme or protective muliple earthing? Thats the important part on deciding how to install your external supplys

[The_Moog]

there's nothing about earthing on any labels, I'm pretty sure its going to need new rods or something.