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Wire for taking power to shed

What type of cable will I need to power and light my shed. will it be 6mm SWA three core? The shed will need 40 metres of cable to reach it from the house.

5 Answers from MyBuilder Electricians

Best Answer

The size of the conductors to use depends entirely on the load drawn by equipment in the shed. Two core may well be permissable also. If there are any extraneous conductive parts within the shed that require bonding back to the main earth terminal this will have an impact also.

This is really something that cannot be answered without either a lot more detail or by looking at the job and properpy designing the installation.

I would add however that anyone who says something along the lines of "pah, sling it in, it'll be fine" isn't an electrician and shouldn't be advising you. Nor is anyone who tells you point blank that "you've got to have an earth rod in there mate".

2015-08-15T11:45:02+01:00

Answered 15th Aug 2015

To be able to calculate the cable size, the load at the shed (i.e. the total power consumption in kW is required). From this the voltage drop based on the Full Load Current (FLC) can be calculated using the tables in BS7671:2008.

Three core SWA could be used if your incoming supply to your house is TNS. If you have a PME(TNCS) supply then you will need to make an enquiry with your Distribution Network Operator to ensure that they are happy for you to "Export" the combined neutral earth to a separate out building (Most DNO's no not approve of this) Therefore a 2 core SWA cable should be installed and a local earth rod driven down into the ground at the shed end, such that the shed is effectively a TT supply with its own RCD at the shed end.

This work comes under part P of the building regulations and before you start you should apply and pay your local authority for consent to carry out the works as DIY. Most local authorities charge around £300 for part P electrical works applications, so you may well find it works out cheaper to hire a registered electrician to do the work for you as registered electricians can self certify their work and register the completed job online with building control on your behalf.

2015-08-15T11:45:02+01:00

Answered 15th Aug 2015

If you are doing it yourself you will have to notify Building Control as if it's a new circuit outside it is notifiable. Cost to you unknown as I don't know what area you are in. A lot of factors in electrical design come into play here. Do yourself a favour and get a registered electrician in to do it properly. As if you go ahead and do it yourself,you risk a fine. This is bread and butter stuff for a competent electrician.

2015-08-15T11:45:02+01:00

Answered 15th Aug 2015

There are numerous considerations to be made when choosing a cable for this purpose. You need to know the expected load, earthing arrangements (is it TT, TN-S or TN-C-S),are you exporting an earth or burying an earth rod? how is the cable being run? What about voltage drop? etc. You really need to get an Electrician to do a proper design calculation to make sure the correct cable is chosen.

Hope this helps

Brendan Mines

2015-08-15T11:45:02+01:00

Answered 15th Aug 2015

Hello.
6mm 3 core SWA cable should be adequate to run a couple of sockets and lights. You should ensure that the cable is connected through an RCD and correct protective device ( max 32 amp mcb ) at source. You should also ensure that the steel sheath of the SWA is earthed using the correct cable glands and 'banjo' clamps.
As this is in a garden it will need to be tested, certified and notified to building control under part-p of the building regulations.
Hope this helps.
Regards.
Chris Smith.
C D Smith. Electrical Contractor.
Leicester.

2015-08-15T11:45:02+01:00

Answered 15th Aug 2015

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