Power to outside garage

23 Sep 2007
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United Kingdom
Hello all,

I want to add power to an outside garage i.e. not joined to the house. I have purchased a “garage kit” that contains a 2 way CU (63A 30mA RCCB, 6A & 32A MCB’s) and SWA (6mm 4 core) to take it to the garage. The garage is about 10m from the main CU; I want to power some lights, freezer, automatic door opener and a few power tools. The main CU has free space for additional circuits but does not have an RCD. I have electrical knowledge (but am not an electrician) and am always up for DIY. The council have been told about it, so is all legal. My main problem is one of choice; I have two options each with their own queries.

1) Connect the garage kit CU in the house, wire the SWA up and take it to the garage. If I did this could I use 2 cores for the 6A and 2 for the 32A circuits (using the armour for earth)? Also what would I use to terminate in the garage; could I just have a metal clad box that the SWA feeds into and 2 outputs for the lights and power or would I need an isolator (or something else)?

2) Take the SWA straight from the main CU to the garage and then connect it to the “garage kit” CU. The sockets in the garage will be RCD protected but will I also need an RCD in the house before the SWA.

Also what MCB should I place in the main CU to feed this, I was thinking about 40A (because 6A & 32A = 38A, 40A being the closest match) but the RCCB in the “garage kit” CU is rated at 63A

Any help much appreciated
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Glad u have notified. :!:

The garage CU goes in the garage. The 6mm runs from your house CU (non rcd side ) You do not need to RCD protect the cable.

You will need 3 cores. These will be live neutral and earth. The SWA armour will also be earthed at the house end.

32A fuse in the house CU to protect your 6mm cable.

Do you water or other services in the garage - there's things to do if you have...

this link gives more info http://www2.theiet.org/Publish/Wire...matters_electrical_installations_outdoors.pdf

Will you be expecting LABC to do all the necessary tests (ELFI, IR & RCD) for you or do you have calibrated test equip?
Thanks for getting back so quickly, I’m glad I don’t have to install an RCD at the house end. Although I will be getting a house rewire in the next year, so do you think I should put the garage circuit into the RCD (I will be installing a split load, so the RCD will already be there) or are there problems in connecting SWA cable to an RCD.

I assumed the LABC would want to do the tests themselves, but it would be better (cheaper) if I could perform the tests myself. Does anyone know if the LABC will allow this? I have not issued plans just a building notice.

PS concerning the rewire when I say I, I mean a sparky.
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If you connect to the RCD in your new, planned, consumer unit then if any fault occurs in the garage then it will trip all the house sockets. If this happens when u are on holiday then you'll come back to a defrosted freezer.

I am assuming that you have space in your existing fuseboard to put in an additional 32A fuse?

From your questions I would guess that you do not have the necessary level of comptency or the calibrated test equipment to test and complete a full Installation certificate to meet what the LABC will expect to see (full compliance with BS7671).

The council are obliged to test it as part of the fee that you've paid - they wont like it but they are supposed to. If they aregue come back here - there are certain documents we can post to help.

If you havent paid for the fee yet, i would strongly suggest that you work with a local competent spark who could do the hard bits (above) for you while you dig the half metre trench for the cable, lay cable on sand, back fill, lay warning tape and all the other things you have to do when running main outside.

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