Extra Low Voltage Lighting

Hi,
I am planning to install ELVL in my new house. I haven't moved in yet to some preliminary questions here to get my started. Please note that I am an absolute beginner so apologies in advance for that. A lot of these are just yes/no answers I think...
1. In regard to lamp and transformer wattage, as I understand it if I plan to have four 25 watt lamps (for example) I will need a 100 watt transformer or four 25 watt transformers. Does this sound correct?
2. However, if I have as in the last question four 25 watt lamps (total of 100 watts), what would happen if my transformer was lets say 150 watt? Would this cause any damage to the lamps or cause them to blow more quickly? I suppose the question here is what would happen if I supplied more watts that absolutely required. Is "over-wattage" a problem or is "over-voltage" what causes the lamps to blow more quickly?
3. What would happen if I fitted say four 30 watt lamps (total requirement of 120 watts) but my transformer was only say 100 watts? I guess that this would put excess load on the transformer and overheat it, so this is not really recommended.
In terms of wiring, I've done some basic investigation but have the following questions:
4. I'm not sure at this stage if the light fitting that I plan to replace has the lighting ring main going direct to a junction box and then to a ceiling rose or the ring is wired directly into a ceiling rose. If the latter I imagine that I will need to replace the ceiling rose with a junction box. Is this correct?
5. After that has been done can I wire my transformer directly to what is the feed for the actual luminaire?
6. If I decide to have one transformer for each light fixture, how can I wire in four transformers? Is it acceptable to terminate the feed to the luminaire into a junction box and then wire the four transformers from this? Or do I need to have each transformer on a separate junction box?
7. If I decide to have a one transformer configuration, is it acceptable to terminate the output from this into a junction box and then feed all four of my lights from that single junction box?
8. If question 7 above is correct what sort of cable do I need to do this? Do I need different cable between the transformer and the junction box than I the need for each light fixture?
Last question....
9. If this installation is to go into a bathroom, does the fact that this is a low voltage installation mean that a specially IP rated fixture is required for over the shower area (zone 2) or is it safe to install low voltage lighting in zone 2?
Thanks in advance for any help received.
Charles.
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Charles Middleton wrote:

Correct
Having a transformer with a higher power than you really need is not a problem, some would recommend it.

Don't do this. An overloaded electronic transformer (the nice small ones) would probably shut itself down ...

Yes.
Yes.
Yes
No
Yes but remember LV means much higher current so if e.g. you use 1mm lighting cable from xformer to the lights then there should be one cable per light i.e. radial wiring and the cables should be as short as possible. Also the wiring from the xformer output to the common point should be only the cable that comes with the transformer, if you need to lengthen it then use 2.5mm power cable.

Maybe see &7.

Yes Anyway afaik Shower is Zone 1 (above the bath to a height of 2.25m). A minimum rating of IPx4 is required here. see http://www.electriclightcompany.co.uk/acatalog/tech_info_bathroom.htm

Not if it doesn't have the required IP rating... What if water splashed a normal LV light? it would explode...

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Not always. Some electronic ones flash the lights on and off slowly if they are under 50% loaded.
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On 04/01/2004 Charles Middleton opined:-

Yes
The transformer would be under rated and thus provide slightly more voltage as a result. This would tend to make the lamps slightly brighter and not last as long as they should. It is the voltage which matters and will reduce the lamps working life, but the over voltage will be a result of the lack of proper loading (watts) to pull it down. Remove all of the load and the voltage may well rise to 16 or more volts, depending upon the tranformers self regulation.

You would be over loading the transformer causing it to over heat and it might well burn out. Tranformers are rated according to the ambient working temperature, the expected amount of cooling and an acceptable working life.
There are two types of 'transformer'. The heavy wire wound traditional transformer and an electronic unit which is very much lighter in weight. The latter generally have a voltage controlled output and will be less susceptable to variations in load. The first type does need to be carefully matched to its load, whereas the second will tend to quote a maximum load.
--

Regards,
Harry (M1BYT) (Lap)
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