wiring extra lights

wakanai · Posted: Fri Apr 21, 2006 11:46 am Post Subject: wiring extra lights

i want to add extra lighting in a loft room. at present one light is in place. can i add 8 50w halogens from the one cable i have at present? It is already a lighting circuit and is fused at the cu as such.

in order to extend the wiring from one light to 8 i had planed to do it using terminal blocks (i think that is what they are called) one wire to a tb with two coming out. both those to tbs with four wires coming out then all four to tbs with a final 8 coming out. then wrap the tbs in electrical tape and fix them to the roof beams behind plaster board and insulation. basically i cant fit all those connections in the junction box i bought.

sorry this is so longwinded but this is my first foray into electrics and im not sure this method is ok and that i have thought through all the things i need to.

Cheers in advance

Steve · Posted: Fri Apr 21, 2006 12:18 pm Post Subject:

AAAAARGH!!! dont use terminal blocks!!!!! Get yourself a few JUNCTION BOXES (those round things with holes in the sides and a few terminals inside) and use these. Under no circumstances should terminal blocks be taped up in insulation. Are you aware the cable will need de-rating due to the insulation?

FOUR HUNDRED WATTS? Is this a solarium? Or just a very large room? I would advise against halogen spotlamps in any room with a ceiling lower than 8 feet - they just dont spread the light out enough.

If you were intending to dim these lights, you would need an 800w dimmer due to the characteristics of halogen lamps.

wakanai · Posted: Fri Apr 21, 2006 12:32 pm Post Subject:

Glad i asked. I thought it was dodgy but theoretically possible so it is good to know why it should not be done.

how many connections can i put in one junction box? is there a limit?

Quote:

Are you aware the cable will need de-rating due to the insulation?

no im afraid not and sorry to say i dont know what you mean by de rating.

Its not a solarium just an odd shaped room and difficult to light, i want it bright (and a tan might be nice). i take this is excessive then? would six make more sense?

As you can tell this is my first for electrics... im not that dangerous and i wouldnt have started with out research

appreciate the help

ban-all-sheds · Posted: Fri Apr 21, 2006 12:46 pm Post Subject: Re: wiring extra lights

wakanai wrote:

i want to add extra lighting in a loft room. at present one light is in place. can i add 8 50w halogens from the one cable i have at present? It is already a lighting circuit and is fused at the cu as such.

As lighting circuits can only support 1380W, 400W is a lot to add to an existing one. What's already on it? How many lighting points?

Quote:

in order to extend the wiring from one light to 8 i had planed to do it using terminal blocks (i think that is what they are called) one wire to a tb with two coming out. both those to tbs with four wires coming out then all four to tbs with a final 8 coming out. then wrap the tbs in electrical tape and fix them to the roof beams behind plaster board and insulation. basically i cant fit all those connections in the junction box i bought.

Why not just run a cable from one light to the next?

Quote:

sorry to say i dont know what you mean by de rating.

http://www.tlc-direct.co.uk/Book/4.3.6.htm
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Steve · Posted: Fri Apr 21, 2006 12:50 pm Post Subject:

4-6 maximum for an average bedroom.

Cable produces heat when you pass a current through it. By putting it in insulation, it cannot dissipate this heat, and might melt if you pass its rated current through it. So cables need de-rating by as much as half when you put them in insulation.

However, for a lighting circuit this is rarely a problem. As long as you have 1.0mm² cable or above, it will cope with 400w of load. Also make sure you clear the insulation above where you are putting the lights - they make a LOT of heat and the lamps will fail prematurely if they get too hot due to insulation.

As for junction boxes - no more than 5 cables per box is about the limit. Any more and terminating the cables will become tricky. JBs have 4 holes in them, but i believe doubling up the cables is acceptable. Also, all joints must be accessible, so put the JBs above the lights.

Good luck - any more questions please do ask!

Pens · Posted: Fri Apr 21, 2006 1:04 pm Post Subject: Re: wiring extra lights

ban-all-sheds wrote:

As lighting circuits can only support 1380W, 400W is a lot to add to an existing one. What's already on it? How many lighting points?

I can never understand why lighting circuits are installed at 6amps when most of the time 1.5mm is used. 10A circuits seem more practical to me.

Gone are the days where one 60watt lamp hung from the ceiling with a green lamp shade.

wakanai · Posted: Fri Apr 21, 2006 1:05 pm Post Subject:

There are 6 other lights running off the same circuit so if they have 100 watt bulbs (they are 60 at the moment) 600 plus 400 would give 1000.

Quote:

Why not just run a cable from one light to the next?

showing how little i knew i didnt think that was the way to do it. the plastic casing over where the wires join doesnt really have room for two cables to enter but i guess i could make it fit but chipping a bit off. it doesnt seem to be any safer than terminal boxes though because the halogen are recessed and the fitting are basically just terminal boxes anyway. it would definitely be less hassle and wires though.

cheers for the link, that website is good. If i leave an inch gap each side of the cable and round the back of the light fittings that would fix the problem?

and does any of this effect P regs?

Cheers

wakanai · Posted: Fri Apr 21, 2006 1:17 pm Post Subject:

im a slow typer.

Cheers Crafty i will use 6 lights instead and one junction box to 2 sets of three lights connected to each other. the cable is 1.5 so i will clear a bit a space around them and hopefully derating will be sorted.

Glad im learning a bit and will know for next time

RF Lighting · Posted: Fri Apr 21, 2006 5:14 pm Post Subject:

Unfortunatly it is required by part P of the building regs that you notify LABC of your proposed work. (Part P document Regulation 4(2) page 6)

As for your joints have you considered these? http://www.screwfix.com/app/sfd/cat/pro.jsp?id=35855&ts=39565

Rob

securespark · Posted: Fri Apr 21, 2006 9:00 pm Post Subject: Re: wiring extra lights

Pensdown wrote:

I can never understand why lighting circuits are installed at 6amps when most of the time 1.5mm is used. 10A circuits seem more practical to me.

Quote:

My take is that 1.0mm2 is good for 6A, and 1.5, 10A breakers.

Gone are the days where one 60watt lamp hung from the ceiling with a green lamp shade.

Yeah. Went to a job yestersday. House had 1 lighting circuit, 5A 3036.

Problem? Fuse blowing. Added up the total load: 2420W

Put them all on, and waited. And waited. And waited.

After 12 minutes 39 seconds, the fuse blew!

The problem in that house was that the original lighting circuit probably only had [/quote]one 60watt lamp hung from the ceiling[quote] in each original room or area, making 660W. Many of the points on that circuit were in additions and extensions to the building.

So, a good case ofr a circuit being designed for a certain load, and being added to over the years to breaking point.

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