Mains feed to garage
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Joined: Mon Dec 08, 2008 12:53 am

Mains feed to garage

by dns » Mon Dec 08, 2008 1:16 am

My girlfriend moved into a house a while ago, which unforunately was previously owned by someone who thought he was a bit of a DIY expert. Sadly, he wasn't!

The previous electric supply to the garage was run on a length of 2.5mm PVC coated twin and earth, which was fed through a plastic pipe in the flowerbed. It was wired into a small fusebox in the garage and the other end was terminated in a 13amp plug, attached to a socket in the dining room...

Naturally this needs sorting out, but I know there are some complications when it comes to doing outdoor electrics these days.

So far I have bought and laid a run of armoured 3 core cable, which I have wired straight into the fusebox in the garage. The other end feeds into the house and has a 13 amp plug put on as a temporary measure.

I have heard from several sources that both ends of steel armoured cable must be terminated properly with glands and the correct junction boxes. Whilst I understand this necessity outdoors, both ends of my cable are inside the buildings. Is this necessary for me, or can I just strip the armour back and run it into a normal junction box?

I have not yet connected the garage to one of the spare MCBs on the consumer unit. I believe I have to get someone who is Part P qualified to do this, is this correct?

I have also found that I have to have an RCD on an outdoor electrical supply. Does this have to be an independent RCD, or can we just use the current one which protects the rest of the house circuits?

Are there any other steps I can take now, to save us money when we have to get an electrician in to finalise everything?

Any answers much appreciated! Thanks!


by ericmark » Mon Dec 08, 2008 9:26 pm

The Part P status is complex as one is allowed to replace items damaged and as a result not a cut and dried answer what I would say however it needs to be safe and I can’t see how a DIY person can do the job you are talking about and be sure it is safe as the test equipment is expensive to hire and not straight forward to use.
The whole idea of steel wire armoured cable is to ensure if the cable is severed it will result in a direct short so it must be terminated correctly at the supply (house) side.
There are allsorts of rules as to how deep, volt drop, earth loop impedance etc. and when submitting to the council you will need to show you intend to comply.
First step is down load the Part P document and read it. If you go to projects there is a link. Take careful note of the forms from memory starting on page 23. Consider if you think you can complete these or not. You will see it says when applying under Part P once accepted by the county council it is their responsibility to ensure it is completed in a safe way. We have seen today how when a council employee makes an error of judgment they are sacked although this may have been over baby P there is as a result there is an unwillingness for LABC to allow any job to take place which may result in them being taken to task so you must show you are very able and follow the rules so don’t install any cables until you have registered the work with the council most likely they will want to see trench before cable is laid and see that the sand and tiles or safety tape are installed. Having tiles or tape on site ready will of course show you do intend to use them, same with a supply of sand.
The RCD is another bit that is not straight forward. If you are using a RCD for garage supply you need to show that should it trip it will not cause inconvenience or danger or it is unlikely to trip. Installing a 10ma RCD would likely show any fault would not affect the house supply.
It is possible all you need is a metal backing box and a FCU or an RCD RCD and a very simple job but also it may require more.
I would say that the best option is to approach an electrician and tell him you want the supply making safe and you will dig any trench required and make good any plaster etc and get a quote. You may find that he will charge very little more than the LABC will charge and it may just not be worth the hassle of DIY.

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