wiring a summerhouse

  • Thread starter Andrew Haughton
  • Start date
A

Andrew Haughton

My Summer House, in which I hope to install 3 double sockets and 2 wall switched ceiling lights, is about 20 metres from the house and about 35 metres from the consumer unit in the house. In this CU there is a spare fuse. Can I safely and legally run a length of armoured 2.5mm cable from this fuse to the Summer House, junction it to standard 2.5mm cable to supply the 3 sockets? Can I also safely and legally run a spur off that circuit, with some kind of fuse presumably incorporated, to form a lighting circuit?
Any comments gratefully received.
 
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Would advise you create a submain, that means taking a circuit out to a CU in the summer house and running circuits from there for lights and power, just been doing some volt drop calculations, and over that length and still have some volt drop left for final circuits, you'll need the following sizes of SWA for the following ratings of submain

16A submain - 4mm² SWA
20A submain - 6mm² SWA (4mm² at a push if final circuits are short)
32A submain - 10mm² SWA (6mm² at a push if final circuits are short)
40A submain - 10mm² SWA
50A submain - 16mm² SWA (10mm² at a push if final circuits are short)

thats just a rough idea, other things to check such as ELFI.

Are you sure you are upto this work? and just incase you didn't know, its notifiable to local building control

will write more when I'm more awake
 
You first need to decide what the sockets are going to be used for....

Although a summer house......a heater or two?
In the summer, lights strung in the bushes and a griddle for the BBQ?
A kettle?
A lawnmower?

With this decided, you can decide on size of supply, and weather you need to provide more than one final circuit to the sockets, in which case you will deffinantly need a second CU in the summer house.
 
Thanks for the ideas. I don't know if I will do it myself but a few years ago I wired a half a house which was then checked over by an electrician and approved so I have a basic knowledge and would get it checked in plan form and on completion and a building warrant will be applied for.
ADAM_151 - Sorry to be so ignorant but what are all those SWAs and ELFIs about? Your advice on voltage drop sounds crucial but how do I work out what I need.
LECTRICIAN - The sockets will run a radio, a kettle, occasionally an electric heater etc. I also have a small shed attached for one of the 3 sockets to supply the odd DIY power tool, nothing too heavyas most are cordless.
What size armoured cable and where can I get it at better than B&Q prices, what level of fusing at main CU.
 
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SWA = Steel Wire Armour (A.K.a Armoured cable)

cable.jpg


ELFI = Earth fault loop impedance, governs the current that will flow to earth in the event of a fault, in the for reference section there is a chart of the maximum allowed ELFI for different protective devices

Volt drop is specified in milli-volts per metre per amp, and its different for different cables, the fiqures are available from tables such as this: http://www.tlc-direct.co.uk/Figures/Tab4.7.htm the maximum volt drop allowed from the supply intake to the end of any final circuit is 9.2v (significance = 4% 230v) with things running at full load.

there is a handy calculator here for volt drop: http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
 
SWA - Screwfix have 2.5mm on offer 16.99 for 25m, also cheap on 4mm. Ebay can also be very cheap. B&Q are a rip off.

Is there anything that will stop me going over the required cable size if i need to add more in future? Say i need 2.5mm/4.0mm i get 6mm to future proof it?
 
Thank you very much Adam. I've checked as far as poss. If this all sounds too tricky for an untrained person to safely plan and execute, do say so!
The distance is actually 30m and if I use Hituf 4mm cable allowing for up to 7KW loading the level seems to be under 30 amps. I presume that means a 30 amp fuse at the central CU supplying the circuit. I also assume that an alllowance of up to 7 KW is adequate for 3 sockets and 2 single lights.
Is this right and can you recommend which type of CU I should purchase for this submain.
 
Andrew Haughton said:
Thank you very much Adam. I've checked as far as poss. If this all sounds too tricky for an untrained person to safely plan and execute, do say so!
Its not necessaily beyond the capabilities of a DIYer, but it does require quite a bit of reading up and expanding knowledge, because an unknowledgeable person isn't always aware that he lacks vital knowledge, oh and you should check with your local building control about how they deal with electrical works notified to them (they should inspect it, and then issue a building regs cert, but they like to drag their heals unfortunatly)

Depending on the way BC works, and the task of learning how to do it (unless its your 'hobby' as it is for many of us here... in which case you'd want to learn how to do it anyway) It may prove easier to have a sparky do it and you dig the trench for the cable for him

The distance is actually 30m and if I use Hituf 4mm cable allowing for up to 7KW loading the level seems to be under 30 amps. I presume that means a 30 amp fuse at the central CU supplying the circuit. I also assume that an alllowance of up to 7 KW is adequate for 3 sockets and 2 single lights.
You want SWA not Hi-tuff, and you want 6mm² for 30A, 4mm² would be ok for 20A, and regarding adequate, very very likely yes, unless you want to fill it with electric heaters

can you recommend which type of CU I should purchase for this submain.

You want one with a 30ma RCD main incommer, and about 4 outgoing ways from a recognised brand such as MK, Wylex or Hager, and ideally metalclad to make terminating the SWA easier

something like this: http://www.tlc-direct.co.uk/Products/WYNHRS506.html

Or this: http://www.tlc-direct.co.uk/Products/MK5508.html together with this: http://www.tlc-direct.co.uk/Products/MK5740.html (which is cheaper from screwfix: http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331830&ts=94482&id=86990 )
 
ADAM
Again many thanks.
How deep does the trench have to be?!
 

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