DIY Doctor

Outside cavity wall lights

Postby Stillia » Sat May 24, 2008 1:31 pm

Hi, a friend of mine has built a cavity wall down the side of his house & is wanting me to put some lights on the top for him. However, to get a supply to them will be tricky as the consumer unit is at the other side of the house, around 40ft away!!
Can anyone help with the following:-
How can i get a feed to the lights without going near the unit?
Where should I mount the switch? inside or outside?
Do I need to use SWA as the wall for the lights is around 8ft away from the side of his house?

Thanks in anticipation, Andy.
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Simply Build It

Postby ericmark » Sat May 24, 2008 6:04 pm

Much depends on what you have so a few pointers.
• Any cables in the sun light will be black, do not use twin and earth as the plastic will degrade you will note nearly all SWA cable is black.
• Spur units can work both ways and is a handy way to change from a flex to SWA.
• Outside lights can get wet and protecting with a 10ma RCD is one way to ensure a fault does not trip out other items in the house.
• House lighting although it can be supplied with up to a 16 Amp overload device often contains items like ceiling roses which reduce this to 6 Amp and some outside lights require this just for one lamp.
• If the consumer unit is 40ft away supplying it from ring main or any other source will not make it any closer and consideration must be made for total volt drop, and earth loop impedance.
• Where you mount the switch should be in sight of the light for bulb changes etc. Or there must be a method of isolation which will make it safe to work on as well as handy for house holder.
• 8ft away from the house could be under Part P. It also may have earthing considerations. If being checked under Part P you will have to ensure everything complies.
You must realise the information you have given is no where near enough to plan what you intend to do. If you were Part P I would not expect the questions you ask which means going through building controls who will require a full plan of what you intend to do with type of earthing system, volt drop calculations, and earth loop impedance calculations. They do not like anyone DIYing and will put up every objection they can as once accepted they are responsible for safety although you still have to test it all and submit all the paper work. Scotland does not have Part P but their regs are even worse. If I were in your shoes first I would follow the links in the Projects section down load Part P and on page 23 you will see copy of the forms you need to fill in. If you don’t understand the forms or haven’t got the test kit required I would back heal the job. It’s not the work that’s hard it’s the paperwork. Also get in writing off your friend who is responsible for informing the council. Also remember the 1st July is now very close with the new regulations even if technically you can go by old regulations I would not bank on building controls letting you do that and would plan to new regulations.

Years ago as an industrial electrician I did many favour jobs, but today one has to be very careful it’s bad enough for those where it’s their official job and they have insurance should any thing go wrong consider what you would do if building control told you to rip it all out and do it again you will lose money and a friend.

All best Eric

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