Correct type of cable for outdoor use. Ask questions and find answers to many subjects relating to electrics and electrical work

[Dadwood]

Hi, I want to fix a 300w security light to the outside wall of my home. The fitting itself is fully weatherproof. But due to the construction of the walls, the final metre of cable to the light will need to be clipped to the outside wall exposed to the elements. What type of cable do I need? Would it be OK to make the whole length in silicone rubber covered waterproof 1mm twin and earth that one can buy for totally immersed fish pond pumps and fountains?

[ericmark]

For a security lamp over 150W you need to apply to the county council for permission. The main thing is sun light which can degrade PVC so normally any outside cable will be black to protect from UV light. Depending on where it may need mechanical protection but normally lights fitted as DIY which have to be on house wall with no external connections for Part P would be OK with any black flex.

Twin and earth and butyl cables are very different and from what you say I would consider you really should be getting the work done for you by an electrician. It would seem from the little you say you don't have the skill and knowledge required. Also it may need registering under Part P and for such a little job the council charges will be higher to DIY than an electrician will likely charge.

[OnlineElectrician]

Hi Dadwood.

You can fit the 300w flood light using 1mm 3 core TRS (tough rubber sheath) cable, it will withstand the elements and sunlight better than PVC twin and earth.

Idealy if this is froming part of a permenent installation it should be in soild core conductors as much as possible, rather that stranded cores.

You don't mention how your going to supply your flood light so i can't comment on how it will fall under the part p regulation.

[Dadwood]

Dear ericmark, thank you very much for your helpful reply. Are you saying that one has to apply for county council permission for ANY outside light over 150W? or can that permission be waived if a fully qualified electrical engineer does the installation? I will certainly take your advice and put the whole job in the hands of someone who is qualified. Thank you again.

[Dadwood]

Dear OnlineElectrician, Thank you for taking the time to send me a useful reply. You will see from my reply to ericmark that the first thing I may need to do is get permission from my county council, and I shall obtain the application forms tomorrow. Once permission is granted (I can't see any reason NOT to get that permission, because I have counted 23 other security lights already installed in my street), I shall call in a fully qualified electrician to do the job. Thank you again.

[jimmy_one_ball]

Make sure this electrician provides you with a Minor Works Certificate upon which he will record his test results.

Insist on this before work commences, your buildings insurance may depend on it!

Also as this conductor will be changing environments such as indoors to outside, it will need to be protected by a fuse, on the inside (such as a fused spur). If he argues then quote Regulation 434.2.1 (BS7671 2008 17th Edition Wiring Regulations).

If, as I suspect, the work is merely an addition to an existing circuit, then under Part P of the buildings regulations, this is non-notifiable work and as such the buildings inspector need not be informed.

Haven't got a clue about this 300W rule, never heard that one before!

[ericmark]

With the exception of foot ball pitches and like I really can't see why anyone need 150W. My Nickel Metal Halide flood at 75W is miles too bright and is only used once or twice a year. Most houses will only require around 22W lamps. The whole idea of course is to dissuade people from using tungsten lighting outside which of course is wasteful however it seems to have escaped their notice that security lamps should only be on for a couple on minutes and discharge lighting does not like such a short time.

However one has to be so careful as it is of course possible that others in the street have not asked permission and you by asking could be causing your neighbours problems. Not asking could also cause you problems. So easiest way is to keep below the 150W limit. Also unlikely council will give permission free of charge. For Part P their minimum charge is £100+ which if all you want to do is fit one outside lamp is a little OTT.

Google earth and like make it very easy for councils to check on outside lighting and although one may break the rules where it is highly unlikely you will get caught it may not be the way to do things when so easy to see.

Part L is to be downloaded here (Google "planningportal.gov.uk/england/professionals/buildingregs/technicalguidance/bcconsfppartl/bcconsfppartlappdoc/") and I think page 41 is where it is all written about fixed external lighting.

[Dadwood]

Dear jimmy_one_ball, and ericmark, Many thanks to you both for taking the time to explain things so clearly. Goodness me, I never realised that such a seemingly simple job as putting up a security light needed such a careful approach. I contacted my county council offices for an application form to get permission to erect the light. I had a long chat with one of their officers who seems to think that the 150W max light regulation only applies to new build or building extensions. It seems that in my case, where I just want to put a light on the outside of a 40 year old house, I don't need to apply for permission. What they DID say however was that the new light needs to be sited and of an intensity such as to cause no nuisance to neighbours. The council chap then gave me the address of an electrical contractor who does a lot of council work. I went to see them and they sold me 5 metres of 3 core 1mm2 tough black rubber sheathed round flex which they said would be perfectly correct for the run both inside and outside. Their design man said that when connected to a 300W lamp, the 5 metre run would give a 0.3 voltdrop and a 1.3 amp load. He said that the simplest way to connect it is by a 3 pin plug with a 3 amp fuse. By doing it this way it seems that none of the regs apply. He suggests that I should plug it into one of the house socket outlets via an RCD plug. This has been a most informative exercise for me and I thank you all for your guidance.