cabling for outside

Postby ajax » Wed Sep 03, 2008 6:55 am

I have looked thru some threads to find some topics on cabling for outside lights etc.. but unfort, it has not been to clear for me.

What i would like to do, is to run a cable, from the C/U to a 6 gang switch, located in my sitting room, which in turn will be for switching on lights outside, plus, if possible, pond pump. Problem is, i'm not really sure what cables to put in. Any ideas ?

One other option given to me, was to put a small C/U under my stairs, specific for the outside items, and run that to the garage main C/U. Is this a good idea, and if som what cables/ratings would be the best.
Its mainly low voltage LED outside, but there are some 220 lights as well.

many thanks
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Simply Build It

Postby ericmark » Wed Sep 03, 2008 7:29 am

In the main for cable outside we use steel wire armoured this cable needs a gland and it is normal to start and finish into a metal box to get 6 cables of this type into a switch backing box would not be easy and you talk of LED lights as well as 230 volt so may be you need to mount transformers? As to consumer units with 6 amp the smallest MCB and LEDs taking milli-amp seems over kill and fuse box for a car for extra low voltage stuff seems more appropriate. I would have a look in Maplin for ideas and also the IET web site look for wiring matters can’t remember which issue but one does out building. Also visit a garden centre with ponds they will give you ideas sometimes one can follow walls etc and SWA is not required maybe so conduit in bad bits but your request is so vague can’t really give a good answer.

Postby ajax » Wed Sep 03, 2008 10:03 am

well, thanks for the info, i'm just trying to get the cable sorted inside the house - ie, from the c/U in the garage, through the house to the back, so whilst the floorboards are up, tried to save a little time.
thanks anyway.
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Postby ericmark » Wed Sep 03, 2008 6:58 pm

Nothing out side that you have listed will require much power and a fused connection unit on your ring main should be enough.
I did the same with my dads house fitted 4 x 2.5 ready to run two new ring mains then he spat the dummy and said no more building work so the just sit there ready.
Without seeing your house it would be hard to advise. For a out building I will normally run 6mm SWA outside the house. But this is only to play safe and most likely you need nothing like that big.

Postby TOPSPARK » Wed Sep 03, 2008 8:05 pm

Why not call in a part p registered electrician and explain to him what you would like to do and then he can best advise you how best to proceed.
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Postby ajax » Thu Sep 04, 2008 10:24 am

hi eric,

i do have the ability to run a new ring main, as all the floor oards are up and the room i wish to have the switches in, is next to the garage, so i could run the cable straight thru to the garage, and to the existing C/U. I am trying to avoid having cables outside, as much as is practible anyway. Would you say this would be the better option, and just using standard ring main cable. The idea I am trying, is to have a 6 gand switch plate in my loung (which is the rrom with no floorboards and backs on to the garage), whre I can open the patio door, as I switch on the outside lights. Mind you, trying to find a switch unit is becoming tough as well. I am trying to ind a 6 gand switch unit, with some form of LED/Lamp indicators on each one, so I know if I have left anything on outside, would you know where I could source something like this ?
many thanks
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Joined: Sat Feb 16, 2008 1:13 pm

Postby ericmark » Thu Sep 04, 2008 1:08 pm

The switch you are looking for is called a grid switch it has a frame with holes and and you can mix and match with fuses and lamps and switches all in same unit. These come in all sorts of sizes expensive. Some options are shown in screwfix which you can view on web. They show as white front 6 unit and as metal 8 unit but I think bigger are available remember wiring is fiddlely and I would go for biggest backing box you can and also anything over 2.5mm cable you may not get in terminal holes but normally 2.5mm is good for 20 amp so should be no problem. See what you think?

Postby ajax » Wed Sep 10, 2008 11:09 am


found some of that grid units you mentioned, and looks exactly what i was after. Many thanks for that.
if i run 2.5 under the floor (ground floor in the house), will i have to have it in any conduit or am i ok to leave it loose under the floor - not sure if its best to or not (in case things nibble at it etc..)

Shame i cant put drawings here as i could show you exactly what i mean.

end result is,
i run 2.5 to the grid switches, from my main CU, if i run 2.5 from the switches to a small space i have in the house hidden away), to 4/6/8 (depending upon how many grid switches) RCD protected sockets, then i can plug in the lights, pump etc.. , and run them with their own cable, in protected trunking, outside to the respective devices ? Does this sound fair ?
Just trying to get all the cables pulled in one hit so i can lay the new floor.

On a slightly different note, and forgive me for asking, i read somewhere that a fridge/freezer needs to have its own seperate supply for the kitchen ? Is this true, i coudnt find an exact answer. I have pulled a 10mm cable for the over (better to be safe), and pulled a new 2.5 ring for the kitchen, but then i came across this independant supply article. could you offer any light/advice on this matter ?

thanks for all your help anyway.

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Postby sparx » Wed Sep 10, 2008 5:41 pm

Ajax, ref your final question .

It is not necessessary to run a seperate circuit for fridge or freezer, the comments you may have seen/heard refer to a line in the 17th regs which has caused unbelievable confusion.
The regs now require virtually all circuits to have RCD protection.
Some people suggested this could lead to loss of supply to freezer if tripped whilst on holiday etc.
So to placate such doom mongers it is allowed now to install a dedicated/marked outlet for such items without RCD protection PROVIDING the wiring method itself does not need RCD coverage;
ie it is surface run, or in special earth screened cable, or in earthed metal conduit, or buried more than 50mm deep.
Personally I think if your RCD's randomly trip out there has to be a problem, especially if house unoccupied,
IN my 45 years in the trade I can only remember one faulty RCD, if they trip there is a fault which needs locating,
Regards, SPARX
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Postby ericmark » Wed Sep 10, 2008 8:24 pm

If you are considering that a plug and socket will get you around Part P then no it will not and if you are using 20 amp grid switches with a bank of sockets this is exactly what is done in many kitchens to isolate washing machine etc. So assuming 20 amp RCBO supply then OK.
But with any installation you must consider all aspects from rodent attack to volt drop and earth loop impedance and although in general terms I see no faults it has to be down to the person on site to make final judgement. Can’t do that for you.
If you follow links in projects section to Part P and down load you will see sample forms think start around page 22 by trying to complete these forms they will highlight any errors as to if you submit them it is up to you but I find even with my experience filling in the forms will often jog me to testing something I had missed and highlighting errors. Same as filling in a risk assessment does not make job safer but can jog one to checking items which would have been otherwise missed. I am uncertain as to Ali-tube and rodent attack but they can get through twin and earth with no problem.
My problem is little pin holes in insulation caused by the rodent repellent i.e. my cat who will ideally chew at cables.

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