Changing to lv halogen lighting

[rumba]

Hi guys.

Just found this forum and it looks really helpful, so i thought i'd join up to seek assistance. This weekend i'm installing a new false ceiling and am changing to lv halogen downlights. I want to make sure that i'm fully prepared and know what i'm doing before i get started, cos it's a lot to do in a weekend. If i mess up, the missus won't be happy going without any bathroom lights until i get chance to sort it out the following weekend.

My previous set up was a two gang switch located in the hallway which operated both the bathroom and toilet light. However, i've since knocked through the wall inbetween my toilet and bathroom, and bricked up the toilet door to create 1 big bathroom, enabling me to fit a shower in the space freed up.

I have 5 downlights to install. I understand i need a 12v 210va transformer. Also i'll need to change the bulbs i have already purchased from 50w to 35w, so they don't exceed the transformer limits. (i forgot to add up the watts and didn't realise i couldn't buy a 250va transformer).

I was surprised when examining the wiring to find that i only have 3 wires feeding the old circuit, and no spur to split it up. i have an earth and neutral going straight to one of the light pendants. then a live to the 2 gang switch. from here, there's a load of fancy wiring and lots of live wires which go back to the 2 pendents. i take it i just take it all out and begin by linking the earth and neutral to the transformer, and then the live to the new cordpull switch located on the bathroom ceiling, and then back to the transformer to complete the circuit.

for this i can use the existing wiring. however, from the transformer to the 5 halogen lights. do i need to get 2 core wiring?

what is the best way to link up the 5 lights from the transformer? via a spur or just in parallel/serial?

do i really need intumescent fire hoods, as they're quite expensive. if so, do i need it for just the lights and/or the transformer too? are the fire hoods easy to install once the plasterboard goes up, or do i need my holes pre-drilled and the firehoods installed on the fixture ends for the lights.

will 5x35w bulbs be bright enough for a smallish bathroom (1 above toilet, 1 above shower, 2 above bath, 1 in centre of the room). were the 5x50w bulbs overkill in the bathroom, or do i need to consider having more than 1 transformer. if so, how will i connect up 2 or more transformers? can i have a mixture of different watt bulbs in the fixtures?

do all transformers hum or buzz, or is this mainly just associated with dimming switches which i won't have?

do i need to get a specific thickness or type of cable for this job?

does this transformer look suitable?
http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=98744&id=10066

how easy would it be to introduce a shaving socket to the mix?

basically any tips or guidance would be greatly appreciated. I'm sure i'll be fine once i get started, as i'm a pretty good amateur diy'er. the only problem is that i've never done anything like this before. i've read up and have emergency contacts incase things go wrong. i guess i just need a pat on the back and re-assurance that things will be ok.

thanks.

 

[breezer]

transformer is ok, but one for each would be better.

as for how to wire them look in for refence, but you will need 1mm t & e

 

[mapj1]

Fire hoods are a must, if the occupier of room above is likely to be unaware of fire below- you are protecting against fire spreading through the ceiling.- usually compulsory if separate flats, not needed if its an unoccupied loft. Use judgement if its your own bedroom above!
Lamps in parallel, note many trannies have multiple terminals for this very situation. place the transformers where they can be reached for service,and will not overheat. (not in insulation for example)
A shaving socket in a bathroom should be a transformer insulated type, and the earth core of the circuit feeding it should be cross bonded to the plumbing, as should the earth core of any other circuits that enter the bathrooom (showers towel rails etc..)

PS, and for info only,
Strictly speaking such work is notifiable to building control under part P building regs, and the council will charge to inspect your work and you may also have to find an electrician prepared to issue a certificate for it. Ask your council building control office for their charges before you start, at the levels many are setting I suspect a lot of people will 'forget' to notify. (As a detail they should already have been involved if you've changed a shower or a WC )

 

[rumba]

thanks for the replies fellas.

being a forum newbie, i didn't see the sticky reference section at the top of the page, so i'll make sure i have a good read of that before i come back with more questions.

dunno why, but i've always found electrics confusing. probably something to do with the fact that i'm partially colour blind, with reds and greens both looking the same to me.

i can honestly say it doesn't inspire confidence when i have to ask the missus if the dark shade of cable is green or red! i'd compare it to someone trying to wire a house up when all the wires are grey, with only subtle changes in shade!

 

[mapj1]

you won't like the new 3 phase colours then, now we all struggle to distinguish live from neutral, particulalry in poor light.

 

[rumba]

so what happens with the earth connection on 1mm t & e? is it just there to future proof in case i change light fittings in future?

how accessible does the trannie need to be? the roof is solid concrete for upstairs flat, so i can't get at it from above. my house is a ground floor maisonette. that's why i'm putting a false ceiling in, to hide the wiring.

could i just attach the transformer to the roof but keep it near to one of the fittings. that way i could get access to it by removing a downlight. it wouldn't be good for maintenance, but at least i could inspect it through the gap.

the only other option would be to locate it outside the bathroom, or hide it behind the partial false wall where the hidden toilet cistern is. neither option i see as viable.

do i need to be extra careful or wiring above the shower?

 

[Steve]

I had a similar situation last year, used a kit though, with cheapo trannies. First time, I attached it to the original ceiling right in the middle of the room, where the old light had been. When that one failed, i just sat the new one (another kit one) on a joist on the false ceiling, less hassle to replace then, plus, i couldnt get at the original ceiling with the false one in the way. Then about 6 months later, that one failed and we replaced the lot with mains halogens. Lots cleaner and crisper light.

If you must use a transformer, i dont recommend mounting on the original ceiling, since re-mounting one here in future will be near impossible through a downlight hole. Just rest the transformer on a joist near a downlight, maybe with one screw, so it can be easily removed and it is secured.

 

[rumba]

so do transformers fail quite often then?

 

[breezer]

proper transformers last for years , there is one supplying your house now (yes ok its big) but the thing is poster did say "cheapo trannies"

as always you get what you pay for and quality costs (that has just cost you £14.52)

 

[Steve]

aye, i wasnt saying all transformers are unreliable, just the cheap kit ones look solid and reliable, but they aren't. The back cracked open and it failed both times. Im sure if you get a decent quality transformer from a wholesaler it will last years.

 

[plugwash]

the "electronic transformers" supplied in lighting kits appear to be some form of cheaply made transformer smpsu (you can make smpsus without using a transformer but they don't isolate)

theese get away with having a much physically smaller transformer by doing the voltage conversion at a much higher frequency

unfortunately the electronics in them seems rather failure prone.

normal transformers (generally torodial at this kind of power) seem to give far less problems but are more expensive, bulkier and you have to be carefull when dimming them (because they have a significant inductance)

 

[rumba]

thanks for all your replies and help.

it's sunday night and i now have 5 fully functioning low voltage lights dangling from my ceiling (and i didn't even electrocute myself once!)


i didn't manage to get the plasterboard put up yet, but all the wooden struts are there so i should probably be able to have it done and dusted soon.