Low voltage downlights. Can I use 0.75mm flex between transformer & lights. What is max cable length possible?

Question

can I run a cable to each light from the transformer or does it have to be one cable or can I split into 2 runs or 5 runs? I am looking at 5x20w lights on a 105mva transformer

Answer 1

With 5 x 20 watt lights on a single 105va transformer you could wire almost any combination with 0.75²mm flex, but I suggest that you use at least two runs of flex. Try to keep the cable length below 3m if possible.

Answer 2

You could use a single cable (rather than flex), with each lamp connected across its two conductors, in turn. However, the cable between the transformer and the first lamp would have to carry about 8.5 amps (100w at 12v is about 8.5A) so you might be better off with 1mm cable.
If you were to connect a separate cable from the transformer to each lamp, each cable would only be carrying under 2 amps, so 0.75mm would be OK. All conductors exhibit some resistance (and hence voltage drop at the business end), but unless a really long run (like garden lighting) is involved, it shouldn't be a problem. The fatter the cable, the less is its resistance, of course.

Answer 3

Unless you are using a CE-marked kit, then the work is notifiable under Part P of the Building Regs.

Regardless of that, when using LV downlights remote from a transformer the wires should be approximately the same length to each otherwise the further ones will be dimmer due to voltage drop in the cable.

The simplest and best solution is to use 1 transformer per light.

Answer 4

presumably you are referring to downlights ? (low voltage surface light fittings tend to come complete with required transformer) as previous, i would opt for a transformer for each fitting, these would normally be rated around 60-65w each, and should fit into the hole in the ceiling, this makes it easier to change at a later date if required. dimmable transformers are also available, make sure you use appropriate rated dimmer switch. it is normal for a low voltage transformer to 'buzz' whilst in operation, more so when dimmed. once low voltage bulbs are nearing the end of there lifetime, you may see a colour change, a kind of blu/purple. I would avoid using low voltage fittings in a kitchen or bathroom, purely because the lights in these rooms tend to be used sparingly, thus reducing the lifetime of the bulbs. for these rooms I would opt for mains halogen, (GU10) which do not require transformer, as they work off 240v, reducing maintenance issues (no trannie to replace later) and low wattage LED bulbs are available for these,downside is the bulbs are more expensive. if in doubt check with a qualified electrician