What size Cable for Low Voltage Down-Lights please ?

[Furkin]

Hi,
I've bought some low watt downlights, 35w halogens, and 105w transformers.

What sort/size cable do I need from transformer to light-fittings please ?

thanks for reading,,,,,,,,,,,,,,,,,

 

[Lectrician]

I assume you mean low voltage (or actually, extra low voltage).

Are you planning on using one transformer with more than one fitting? For the cost of a transformer these days, you are best fitting a 60va tranny directly behind each fitting and not using any additional cable on the ELV side. You just first fix as if the lights are standard mains voltage.

But to answer your question, the cable size depends hugely on how long the run is. You should really only have a single light per cable too. If the cable is running in thermal insulation you really do need to be careful, more so with the ELV.

 

[Furkin]

Thanks - yep - I did mean low voltage (12v) I knew I shouldn't have rushed the post before tea !!

I purposely bought 105w trannies specifically to run 3 x 35w lamps from each.

All the previous L.Watt stuff I fitted were in 'Kit' form (105w tranny + 3 x lamps + single cable). The lamps ran in series.

I had planned to do similar. Eg: run 2 or 3 lots of 3 lamps in my kitchen ceiling. The insulation is 'glass' fibre.


Hope this helps you to help me.

PS: What's the benefit of using a 50/60w lamp with own tranny ?

 

[breezer]

The lamps ran in series.

I hope not. Look in the sticky for a picture of "in series"

There are a couple of reasons for 1 light 1 transformer

1) transfromer dies = no lights at least with multiple transformers you still have other lights on.

2) you can use a smaller cable to connect mains to transformers*

* sorry I cant quite put it right, i seem to be stuck for the right words

(Bigger cable required for higher current)

3) no wondering which light the transformer is next to (with one light one transformer the transformer is next to the light.


Oh, and as an aside, electronic transfomers dont last that long. I am going to try toroidial transformers

 

[Furkin]

Thanks Breezer,

SERIES: You are totally right,,, although I didn't actually mean 'wired in series',,,, I meant a a single (twin) cable to lamp connector One,,, then on to connector Two,,, then on to lamp connector Three.,,,, rather than a separate cable to each lamp.
I'm sorry to lie !?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For the time being, I have 24 new downlighters & 35w lamps, and 8 x 105w trannies.
Obviously would prefer to use them.

Then i'll look into the other method next time - which goes back to my original quest - plus:
To use my 3 lamp set-up, would it be better to use a lead to each lamp from the tranny (seems wrong to my limited mind) or a single (twin) cable to lamp one,,,, on to lamp two,,,, on to lamp 3 - in parallel ?
In either case - what size cable would I need ?

thanks for your patience.

 

[Furkin]

just to add:

Cable runs - from tranny to fittings - would be around 3m in all cases. (reminder: 3 x 35w lamps from each 105w tranny).

What size cable would be needed please ?

 

[ban-all-sheds]

I purposely bought 105w trannies specifically to run 3 x 35w lamps from each.

All the previous L.Watt stuff I fitted were in 'Kit' form (105w tranny + 3 x lamps + single cable). The lamps ran in series.

I had planned to do similar. Eg: run 2 or 3 lots of 3 lamps in my kitchen ceiling. The insulation is 'glass' fibre.

If you're in England or Wales this is notifiable work.

And it's notifiable everywhere, not just kitchen and bathroom, because you aren't using a kit.

24 x 35W lamps - will this light the place up as much as 8 or more 100W GLS pendants?

2-300W just in the kitchen - will that do as good a job as 5 x 5' fluorescents?

If the answer to either of those questions is "no" then you have just realised why you should not be installing this type of lighting in the first place.

And you'll have to make sure the insulation is kept away from them, but you can't just clear it away because then you'll compromise the overall insulation of that building element, contravening Part L - you'll need to build or buy something to go over the top of the lights and then take the insulation over and around that.

And in kitchens and bathrooms you'll need to seal the cover to the ceiling to stop warm moist air entering the unconditioned space or you'll contravene Part C.

If you have no access from above then you won't be able to do either of these things.

 

[Furkin]

thanks BAS:

The kitchen is approx 4.8 x 1.8m. It originally had a 60w pendant.
I replaced that with a 4ft flouro when I moved in.
I was thinking that 6 or 9 x 35w would suffice.
(I do have some 50w halogens,,,, but only a couple of 60w trannies)

The place is a bungalow - so the fireguard fitting is not a problem.

What size cable from tranny to 3 x 35w lamps please ?

 

[Pensdown]

I would run 3x1.5mm cables (one cable per light) from each transformer.

 

[Furkin]

PD: Many thanks.
After reading some of the comments on these pages, I am now wondering if 6 or 9 x 35w items will be enough for the job.

I may end up using 50w items in the end - so a bit of experimenting will have to be done.

unless: there is a chart/table somewhere showing comparisons/needs etc to replace a single 60/100w bulb with 12v items,,,,,, or how many / much 12v's (watts) for a ceiling of approx 8.5sq m.

is there such a thing ?

thanks to all who helped

 

[Steve]

You dont need 800 watts of halogen light in one room (or otherwise). Jesus christ, it'll be red hot.

Fit mains voltage fittings and sell the ELV stuff on ebay to another mug.

The benefit of mains voltage is you can fit energy saving lamps, which are ideal for kitchens. 9 watts instead of 50? I know which I'd choose (and have, and very happy with it)

With the price of energy you dont need to be wasting money on electric guzzling low voltage downlights. (50 watts is 50 watts at any voltage, they use no less energy)

 

[ban-all-sheds]

thanks BAS:

The kitchen is approx 4.8 x 1.8m. It originally had a 60w pendant.
I replaced that with a 4ft flouro when I moved in.
I was thinking that 6 or 9 x 35w would suffice.

They'll be useless.

The place is a bungalow - so the fireguard fitting is not a problem.

You don't need fireguards, you need something to keep the isulation away, and in the kitchen and bathroom you need that something to be completely sealed against the top surface of the plasterboard to stop air getting into the loft. Intumescent hoods or Fireguard type lights won't do.

NHBC downlight installation guide: http://www.nhbcbuilder.co.uk/NHBCpu...ical/StandardsExtra/filedownload,21353,en.pdf

Pre-formed cap to seal downlights: http://www.aico.co.uk/firecap_loftcap.htm

What size cable from tranny to 3 x 35w lamps please ?

http://www.tlc-direct.co.uk/Technical/Lighting/VoltageDrop.html

 

[Furkin]

thanks guys,,,,

I thought I was being too clever for my own good,,,,

STEVE: I only mentioned that I had 24 fittings/lamps etc,,,, not that I was going to use them all. As per the post, I was thinking of either 6 or 9 for this kitchen.

I am now doing a complete re-think. Whilst running costs are one of the primary concerns,,,, so is the cost of fittings,,,, and the 'modern' look of ceiling lights.

I have nothing against mains voltage as such - I just thought that low voltage would be cheaper to run.

BAS: Thanks for that as well. Never seen the 'caps' before. Are they suitable for mains powered fittings as well ?


The next job was to be bathroom,,,,,,, are these caps suitable for that as well ? If not, what else would I need ?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Right:
If I go down the mains power route, how many d'you think i'll need for the kitchen ?
What is the wiring sequence for this method ?
What shape are the 9w Energy Saving Lamps/fittings (same as MR16's ?)

Sorry for the new questions - obviously I hadn't considered this.

thanks again for your patience

 

[ban-all-sheds]

I am now doing a complete re-think. Whilst running costs are one of the primary concerns,,,,

That should rule out any form of small diameter recessed lighting using incandescent lamps then...

so is the cost of fittings,,,, and the 'modern' look of ceiling lights.

Widen your search - consider other types of ceiling lights, and if you must have recessed ones go for much larger than 50mm/2".

I have nothing against mains voltage as such - I just thought that low voltage would be cheaper to run.

A watt is a watt. You get marginally brighter light from ELV ones, but not enough to allow you to get away with fewer of them.

BAS: Thanks for that as well. Never seen the 'caps' before. Are they suitable for mains powered fittings as well ?

Yup.

The next job was to be bathroom,,,,,,, are these caps suitable for that as well ?

Ideal, as you can easily seal them to the ceiling. Silicone I guess...

Right:
If I go down the mains power route, how many d'you think i'll need for the kitchen ?

Don't know - lots - they don't spread well, and the light all goes downwards.

What is the wiring sequence for this method ?

Same as any other lighting. I think you need to get a book or two on the fundamentals of domestic electrical installations...

What shape are the 9w Energy Saving Lamps/fittings (same as MR16's ?)

CFLs are bigger (longer, still Ø50mm), but you can get LEDs with MR16 envelopes. I don't think you can get ELV CFLs though, with GU5.3 bases - they'll all be LV ones with GU10.

 

[Pensdown]

If I go down the mains power route, how many d'you think i'll need for the kitchen ?

In Kitchens, as a rule of thumb, for ELV or mains down lights fitted with a 50watt wide beam lamp, somewhere between 850 - 1000mm centers is about right. This is based on a ceiling height of around 2500 and 400-500lux on the work top.

I’ve never used CFL’s in down lights but assuming the beam width is similar the centers should be the same.

Try to design your layout & switching with energy saving in mind. For example, you could switch every other fitting so that when the Kitchen is not being used for food preparation you can half the light level and the cost