DIY Doctor UK DIY Forums

At the moment I have a two gang switch (both dimmers) one for 3 x 50w halogens, the other 2x50w halgogens.

The 2x50w is redundant and I'd like to use it for under cupboard 18x20w G4 LVs. These would run off two transformers, both 200VA capable for running 10x20w each.

- Firstly, is this possible/sensible?

- Secondly, if it is, what is the best way to hook up the two transofrmers (I'm assuming I will need new ones as I will be cutting into the mains before before it goes into the ceiling void.

- Thirdly, on one end the transformers have two 'inlet terminals (presumably for the mains connection) but each only has four terminals on the other end to take the lights, so I cannot see how I can wire up 10 lights? ........or would I need to use a junction box.

Any help greatly appreciated, inlcuding advice on cable sizes, correct junction box, amp fuses etc

Many thanks, Malc

1. Although you can dim a quartz halogen bulb to do so will shorten the life of the bulbs. They are designed to run with an extremely hot envelope to reflect the tungsten from the quartz so it is re-deposited on to the tungsten.
2. To run an inverter (Most extra low voltage lamps use inverters not transformers) from a dimmer unit they need to be matched. There is leading and lagging types and some inverters will not dim. The whole idea of the inverter is to correct the voltage to within very strict limits so that the envelope and filament are maintained at exactly the right temperature so they give a very white light and have a long life. Adding a dimmer completely defects the whole idea of using an inverter.
3. In order to maintain the voltage the lamps need to be very close to the inverter. So often one inverter per lamp. Hence why not designed to have many lamps per inverter. The one exception is where two thick rails are run and lamps are hung off the rails.

If you want to dim then using GU10 low voltage (230v) lamps is likely better than using extra low voltage (12v) version. Where many lamps are used the normal method is a 1/3 and 2/3 split so giving three lighting levels without changing the colour. Also this method will also work with LED and Cold Cathode versions. Cold cathode are only done as low voltage (230v) not extra low voltage.

To put control gear (inverters) into a ceiling void may be a fire risk. It does need to be a type designed to be used in that way.