Advice on SELV Installation - Please!

[landbeach]

After several weeks following these forums and piecing together comments from archived threads concerning SELV lighting I’ve formulated the following plan and would welcome comments as to whether it seems reasonable:
Currently I have a single loop in/out pendant operated by a single gang switch in a 14’ x 11’ ground floor room with plasterboard ceilings with chipboard T&G flooring over.

I’m proposing to install 9 x 35w SELV downlighters, split into two circuits of 5 and 4 and think the best way forward is as follows:

1. Replace the existing ceiling rose with a junction box with the switched live feeding 2x TLC Premium Electronic (Varilight?) 105 VA transformers, each powering 2 X 35 W downlighters.

2. Adding a second junction box to the existing loop in/out live feed, install a 2-gang Varilight IQ touch/remote dimmer (TLC VLIS1402) and route a second switch cable to the new junction box. Connect the switched live to a 150VA Prem Electronic Transformer supplying 3x35 W downlighters and a 105VA transformer supplying the final 2 downlighters.

I reckon 9x35 Watt lights will provide sufficient light, but may want to exchange a couple for 50 W over a desk area if the luminance is not up to scratch and therefore have proposed transformers that could power the same number of 50W lamps. I also want to ensure minimal LV cable runs, hence the use of several transformers/2 circuits. I realise that the general advice is to have one transformer per lamp but cost/practicality mean that this isn’t my preferred option. Therefore, my questions are as follows:

1. Does the setup appear reasonable/practicable?
2. Is there any recommended minimum/maximum distance between the two junction boxes?
3. Does anybody know how many watts per gang this dimmer switch can handle? (Can’t work it out from the TLC pages, but it appears it could be 250-300W per gang, which would be fine).
4. Not having seen any of the transformers in the flesh, I presume the switched live/neutral cable just daisy chains the transformers via the input terminals on the transformers – with the earths joined together to maintain earth continuity - is this correct?
5. Is it OK to power different wattage lamps from the same transformer, or would I need to change all the lamps powered by that transformer.
6. Is there any disadvantage of having “spare capacity” in a transformer, eg total wattage of lamps 70W, transformer 105VA, or lamps 105W, transformer 150VA?
7. If I did decide to have one transformer per lamp and went for the 70VA Prem Electronic transformers, would it be OK to run 5 transformers off one gang of the dimmer and 4 off the other (still obviously with the two circuits, same lamp ratings etc)? (TLC state you can have up to 10 per circuit and to use the lamp ratings, rather than totting up the VA ratings, but I want to make sure the dimmer could operate those transformers over 2 gangs).

Phew, that’s it!

 

[biggles]

sounds a bit what i wanted to do last weekend but i got confused by all the differennt fittings etc in B&Q. Nobody seems to be clear on what the best transformers are or whether to use mains lights etc.

I've given up for the moment - will wait until I can get a spark in to do other work as well.

Good luck


Biggles
1st man on the moon

 

[breezer]

Nobody seems to be clear on what the best transformers are or whether to use mains lights etc.

you didnt ask here

torodial transformers are best

12v lamps are better than 240 v lamps (IMO)

 

[biggles]

but i read people have problems with dimming torroidals, they are bigger and can't fit through the holes in the ceiling and so you end up with longer lv cable lengths and they're more expensive. Is this right? If they are the best choice, why do all the ready made kits have electronic transformers?

 

[Big_Spark]

you didnt ask here

torodial transformers are best

12v lamps are better than 240 v lamps (IMO)

I totally agree with breezer's first comment, however as the best 12V lamps have a maximum life span of 3000hrs, and 230V lamps can have life spans upt to 15000 hrs, I don't see how 12V can be better.

I'll grant you that if your talking about Dichroics the life span is about the same, but even here 230V Dichroics do have the edge, averaging about 25% longer life in real world operations.

Regarding the choice of manufacturer, ONLY three are worth considering if going for 12V dichroics or other halogens, JCC Lighting, Illuma and Aurora.

Anyone here will tell you I deplore electronic Tx's, however Aurora make a range of them from 105VA up to 250VA that are bloody excellent and they do last the test of time..the reason being is the actual reduction is voltage is achieved with a small wire wound autoTx, the input and output being controlled electronically to prevent spikes and surges from causing damage to the Tx and the lamps.

 

[Big_Spark]

but i read people have problems with dimming torroidals, they are bigger and can't fit through the holes in the ceiling and so you end up with longer lv cable lengths and they're more expensive. Is this right? If they are the best choice, why do all the ready made kits have electronic transformers?

People who complain toroidal are this that and the other do not understand QUALITY.

A toroidal Tx will out perform an electronic Tx hands down, and it will out live 100 fold. I have small 60 and 60VA wire would Tx's that had been in service for about 20 years, they have been removed as the place was refurbed. I installed them as a freeby in a Charity place to save them money...that was FOUR YEARS ago, and they are still going strong.

Incidently..toroidals do not give any problems with dimming if the correct dimmer is bought..ie a quality unit instead of a cheap pile of crap which is what a lot of people buy.

This same very problem causes issues with electronic Tx's..but with these they can and often do, cause damage to MCBs protecting the circuit as well...it also shortens the life of the Tx and the lamps.

 

[landbeach]

Thanks for the responses - however, now I'm not sure if I was ever on the right lines at all!

How would I achieve my goal of 9 x 35 W downlighters on two circuits with torodial transformers? What rating transformers would I need, how many, what type of dimmer etc?

I feel I'm now back to square one - I know what I want to achieve, but don't know the best way of doing it!

Heeelllpp!!!!!

 

[Big_Spark]

A lot will depend on may things, which we don't know about here.

You can buy toroidal Tx's in ratings from 25VA up to 3500VA, however when you start installing toroidals above about 200VA there are two VITAL things you need to consider.

• 
  1: Location of the Transformer..they are large and heavy!
  
  2: Heat dissipation, this is true for electronic ones too, but especially for toroidals at this rating.

 

[securespark]

2. As long as cable between jb's is carrying mains voltage, it is OK. You are limited as to how much cable you can use to carry the secondary voltage.

3. The following has been copied from the Varilight instructions:

When using electronic LV transformers add the VA ratings of the transformers, not the wattage of the bulbs. There is an absolute maximum of 5 transformers, except with VARILIGHT LV Transformers when you can add the bulb wattages up to the dimmer "max. load" with up to 10 transformers.

4. Yes.If the tx's have flying leads, you can use a small 20A jb to connect.

5. Yes, as long as you respect min & max loading.

6. Not usually with intelligent tx's. They can run below full load, but double check with mfr.

7. Guess what you say is OK, but no harm in double checking with Varilight - their number should be on tlc website. If not ring branch.