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Discuss Wiring 240v downlight in the Commercial Electrical Advice area at ElectriciansForums.net

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DonaldJ

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Evening all,

Further to my previous post I've decided to use 240v downlights in the utility room.

Just wondering what the best, well, correct, way to connect these up?

The lights are double insulated and have a little junction box attached with two heat resistant flex's from the little junction box to the light. Now, should I just run 1.5mm cable to each light in sequence, from one to the other but with the earth joined in a choc block (basically meaning that all but the last light in the chain has two conductors in each terminal)?

The alternative I was thinking about was to run a short length of two core flex from the junction box attached to the light to a small 3 terminal junction box and have the 1.5mm circuit cable connect in this juncion box by each light.

How do you do it? What is generally best practice?

Another thing making me nervous is the amount of insulation up in the ceiling which I suspect is a contributing factor in the melted wiring situation on the old 12v lighting in there. I've cleared as much of it out as I can, about 6" around each hole so I think all connections should be OK but I'm worried about the cable run between each light.

As I can't remove the insulation between one light to the next, I was wondering if it is going to be OK if I can make sure the cable lays on top of the insulation rather than sitting under it? I'm using 1.5mm t&e. The lights are 50w each and there are 5 in total so 250w altogether. The last light in the chain will be about 4m away from the first. As I see it, the cable will be carrying just over 1 amp which under ordinary circumstances would be fine for 1.5mm but what de-rating effect ould the insulation have?

Cheers

Don
 
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S

Shakey

  • Thread Starter Thread Starter
  • #2
why are you using 1.5?

even totally surrounded by thermal, derating factor is maximum of 50%

1mm clipped direct is 16A, so even derating it maximim would allow 8A

people always overkill on lighting circuits!
 

Had8Lives

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Arms
If you want to use 1.5mm go ahead, could be useful if lights get changed in the future and it will hopefully feed through the ceiling on top of the insulation better than 1mm which has a nasty habit of bending :-o Regarding the earth, probably best to use a junction box by each light, but run T&E to each light and sleeve the earth and tape it back onto the cable, it's there for future use then.
 
D

DonaldJ

  • Thread Starter Thread Starter
  • #4
why are you using 1.5?
Because it's consistent with the 1.5 that's already in place from the switch, which is buried so I don't fancy digging it out. I figured it better to use the same cable throughout a circuit than different bits here and there.

even totally surrounded by thermal, derating factor is maximum of 50%
Cheers, so 1.5mm is fine then

people always overkill on lighting circuits!
Maybe, maybe not but 1.5 is no less workable than 1mm anyhow.

Cheers

Don

If you want to use 1.5mm go ahead, could be useful if lights get changed in the future and it will hopefully feed through the ceiling on top of the insulation better than 1mm which has a nasty habit of bending :-o Regarding the earth, probably best to use a junction box by each light, but run T&E to each light and sleeve the earth and tape it back onto the cable, it's there for future use then.
Cheers had8,

I've got some pokey rod things which I've had a few years and used a few times which make it easier to route cable over insulation etc so 1mm probably would have been fine but some of the eisting cabling is 1.5mm so wanted to keep it consistent. I'm guessing most people here have something similar.

So you reckon junction box each light rather than using the enclosed terminal block connector on the light as a junction box?

I've been working on it this afternoon and that's what I've done but used heat resistant twin core flex rather than t&e. Got as far as putting the whole circuit together and sticking the jb's into the ceiling with the flex hanging out. It wont be too much effort to change the flex for t&e in the morning. Then just gotta connect each light and fix in place.

Thanks again,

Don
 
Last edited by a moderator:

Had8Lives

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Arms
Glad my advice was useful Donald. I'd agree best to keep cable size consistent. The only reason I'd use T&E to each light is if someone stupid put a screw through the ceiling next to the light, at least it will earth out then. I've installed downlights both ways, using the downlight connector block as a junction box and using a seperate junction box, only problem is two 1.5mm wires don't fit in the downlight block very easily, and then there's trying to get the cover on! Don't worry too much about getting the oute insulation of the T&E inside the downlight enclosure, but be careful you don't tighten the cover down too tight and break the insulation on the conductors. Rods are marvellous! I use them all the time, saves so many floorboards when you're doing a rewire :-D
 
D

DonaldJ

  • Thread Starter Thread Starter
  • #6
Yes it was useful, thanks - helps ease my mind too knowing I seem to be doing things correctly. Just a shame I was impatient and started yesterday afternoon rather than waiting until today. About to start changinf flex for cable now an then just need to wire in each light and switch the lot on.

The fan is already wired in - what a PITA that was getting the permanent live into the 4 wy junction box! I know I've ballsed up on the fan though because I haven't connected it to a Dp isolator between lighting circuit and fan. What there is though is a FCU between ring main and lighting circuit which will obviously cut the fan - do you think that would be acceptable?

When I started working on the lighting circuit yesterday I found an easy way of feeding a 1.5mm cable to the CU to connect directly to the downstairs lighting MCB. However, I wasn't sure if a spur in this way would be allowed (although I can't see why not) and also, I'm sure I read somewhere that fitting a light in Zone 1 requires RCD protection. Now, my shower light is actually just outside Zone 1 but even still, I figured it best to take te feed off the radial circuit via a 3a FCU because the radial is on the split load side of the CU.

Thanks again,

Don.
 
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Reply to Wiring 240v downlight in the Commercial Electrical Advice area at ElectriciansForums.net

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