Lighting for beamed ceiling?

[MdB]

I suspect that the thinner cable can be used because the length of cables are precut and the ease of installation is balanced against the loss in efficiency in heat from the cable. A 12v loop of the same length as a standard lighting circuit would be a terrible idea.

Be very very careful about this. The amount of current a cable can take is independant of its length. A short length of cable with 10A going through it will get just as hot as a long length of the same cable with 10A going through it.

Just to make this clear, a little 35W, 12V bulb requires 3A to flow through its cable where as a 100W, 240V bulb requires only 0.42A. This is a factor 7 difference and hence the low voltage bulb needs a cable 7 times thicker for a fraction of the light output.

In my previous house, I had a string of five 12V 35W halogen bulbs which I wanted to switch on and off at the low voltage side. This meant I could not use a standard lighting switch as these are only typically rated as 10A. After a long search, I found a suitable 20A switch which was capable of dealing with the 15A load. (If I has switched these lights at the 240V input, the current would have been only 0.7A so any old mains rated switch would have been fine)

 

[philpjuk100]

Yes lighting is a problem with low beams,in the kitchen there are 70s type spots mounted on a rail (now with energy saving lamps) they were in the house when we bought it and we are unable to find anything better to replace them with.They cannot normaly be seen unless you are underneath them.we also have a "chinamans hat" over the table where you are unable to walk into it.
I used some led downlighters in a spare bedroom which I got off ebay,the units came with poorly translated instructions,they were 120volt! but I had two transformers so wired them in series,the transformers and lampholders were polarity marked and I think the instructions say if the lamps are dim "unbrightness!* take them out and turn them around! but in fact if you turn them round they give no light at all,take care shopping! attached a couple of pics of our kitcken lighting,phil.

 

[Flyfisher]

Be very very careful about this.

Hear, hear.

Here's a useful calculator: http://www.tlc-direct.co.uk/Technical/Lighting/VoltageDrop.html

Low voltage lighting might be safer from an electrical shock perspective but the high currents involved means that cables and switchgear require suitably high ratings, as MdB has explained.