Low voltage downlights versus Mains voltage downlights.

18 Oct 2007
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United Kingdom
Intended installing low voltage downlights through out my new build house thinking there would be a saving on power consumption, but my spark has advised against as he says low voltage are very troublsome with regards to bulbs and transformers constantly failing and needing replaced. Over to you guys - should i take heed of my spark, 12V 0r 240V? 12V downlights have been around for a good while now - surely transformers and bulbs are more reliable than previously? Any advice on where to get good quality reliable one`s?

Cheers, Seumas
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You get what you pay for. Buy cheap transformers and they'll fail quickly. Same with bulbs.

Low voltage halogens provide a more pleasing light in my opinion to mains halogens, and fail a lot less spectacularly (I've had several GU10's shatter when they've failed).

In terms of the future, you can easily get hold of CFL replacements for GU10's whereas LED replacements are the only alternative for low voltage halogens. The LED replacements available to joe public are pretty dismal at the moment, but I have a set of sample 5, 10, 15W LED replacements for 12V halogens which are ridiculously bright (and of course instant full intensity light when turned on) but are out of the price range of most home users, but with the rapid drop in prices of these power LEDs from Lumileds and Edison Opto it shouldn't be long before they are less than £10 a piece...
If you are set on 12 volt lighting in a new build then you could consider this option.

A single transformer supplying a 12 volt AC supply to all the lighting.

It has been done and while not cheap ( in fact expensive ) did provide reliable low voltage and extremely flexible and adaptable lighting.

Using low voltage control circuits with relays or contactors adjacent to the lights the switches could be very compact and also intelligent.

For the house concerned it also had the advantage of being able to run on batteries during the frequent power cuts.
The downside is to do it with acceptable voltage drop requires pretty heavy wiring. Reduce the voltage by a factor of 20 and the volt drop problem gets 400 times worse.
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Cable cost was the major reason for the high price and why indirect control ( enabling small gauge wire ) was used.
Oh! and don't forget part L of the building regs which requires 1 in every 4 light fittings to be of low energy type!!
however a 50w low voltage light fitting is going to use exactley the same power as a 50w mains voltage fitting. 50w is 50w! therefor the only way you would save on power consumption is if you are using fewer fittings. And the Part L argument is quite important. approx 1/4 of rooms must be 'LOW ENERGY' i.e energy saving 11w flourescent lamps in non-adaptable fittings.
I don't think it's 1 in 4 rooms any more, the latest edition of part L1 & L2 changed it to 1 in 4 fittings!
Very interested in what you did with 12v supply to all the lighting - particularly in the bit about the lights being able to run on batteries during powercuts, as i stay in an area that suffers from frequent powercuts evey winter!
Where can i find out more about this, such as where to buy and installation?
It wasn't something I did but something I took and interest in while planning out house.

The notes I made should be in the attic but finding them may not happen until the weekend.

The majority of lighting was 12 volt flourescent units either bought in or self made. Some incandescent lamps. Series / parallel switiching used to give bright and dim options on the incandescents.

The batteries were traction batteries ( fork lift truck ? ) and fed the lights in the absence of mains power to the transformer / rectifiers ( power was DC ). Cannot remember the details of change over.
If you want max light level for a given wattage, LV is best since the light is whiter and brighter, so in a kitchen LV is great, but of you want more atmosphere say in a snug/sitting room, I'd go for the softer more yellow mains halogens.

The real issue for me is the fire risk in LV downlighting circuits. No one wires them up safely in my view. Mains wiring at each junction box is consistent ie single core flat twin and earth (at least 1mm). Standard 3/4 way Junction boxes of various power ratings are designed to be used with this type of mains cable. With LV, most sparks recommend individual transformers since they are easy to install and replace through the hole where each downlighter goes. The problem is that they are pre-fitted with light duty flex which qualified electricians happily stuff into mains connection terminals in mains junctions boxes. That typically ends up as three six mixed flex/single core connections two terminals plus two earth connections per junction box. You can't guarantee a proper joint if you mix flex and single core in this way, so that's 48 fire risks for 8 lights. because the electricity frequently arcs in loose terminals which is the cause of many fires inside ceilings.

Over time, screw terminals often work loose, but why ? First they may not have been srewed up correctly. Then copper wire is basically soft and gives way under pressure over time after it was screwed up tight. I have also heard that terminal loosening is encouraged by the oscillating mains power supply.

So the only safe way to connect a transformer's LV flex to a single core mains cable is to use a teminal block with dual linked terminals for each connection ie one for the mains wires and one for the flex. I've never seen this done with downlighters !

The probelm with usin one big transformer is first where to put it so it is accessible and how to cable the emerging LV ciruit to all the lights. This requires careful planning to avoid voltage loss and uneven lighting levels.

Hope this helps

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