I plan to install some IP44 rated LV downlights for my wetroom and I'm just wondering the correct way to go regarding wiring these up. I will have 6 in total. A few questions spring to mind:
Should I RCD protect them and if so how? I am only familiar with an RCD on a socket
Is IP44 ok for above a shower, distance from fixed head is about .5 metre. I was looking at IP65 but it looks as though IP44 should be ok.
Should I run each transformer from a single junction box or should I use multiple junction boxes? if multiple how do I go about doing this, do I just daisy chain them having a live out and a neutral out and so on and so forth and running the switched live between them?
Whats the formula to determine if my existing circuit will be capable of the extra load? how do I work all this out.
In a word, no. They're LV, no direct connection to the live, more likely to get hurt slipping in the dark after a nuisance trip than get shocked. You're not going to fiddle with the transformer input wiring while showering, are you?
If they're in the ceiling, IP44 should be just fine - no chance of the ceiling getting sprayed, is there? If you're running them down the wall of the shower cubicle (for all I know you're going to put a webcam in there and earn some extra cash ;-) you'd need IP66 or similar...
Really depends how close they are to each other, and whether you're going for integral-transformer fittings or simple LV fittings which need an external transformer. For the integral-fitting case, it's really a don't-care which comes down to your own wiring convenience - a daisy chain feeding N, E, and switched-L from one to the next is fine, a star-wired large (30A) junction box - just because you need the room, not because you'll be pulling anything remotely like that at 240V - with all 6 feeds from it is fine, two JBs each radiating out 3 feeds (with the first one also having mains-in, switch-return, and downstream-feed, so 6 cables all told) is fine too, or first JB with 2 lamp feeds and a
4-feeder coming off it, or three JBs each feeding 2 lamps - all are just fine.
If you've got separate transformers, it's OK to have a separate transformer or electronic equivalent for each lamp - then wiring the mains to them is just as the integral-transformer case above. But you may find it sensible to buy, say, 2 transformers each rated at 3-4 times the wattage of one of your fittings, position them so they're each fairly close to 3 of your lamps, and run the switched-mains to them (either daisy-chained or star-wired). Only thing to watch in this case is to use thick enough wire on the LV side, and keep it short. That's because supplying 50W at 240V needs just over 0.2A (50/240 is near enough 48/240 for current (ha ha) purposes, and the 0.08ohm there-and-back resistance of a couple of metres of 1mmsq will drop
0.2*0.04 = 0.008V, an utterly negligible proportion of the 240V supply. Feed that 50W load at 12V, and the current goes up to 4A (50/12 = 4 near as dammit); the 0.08 ohm of the same 2m of 1mmsq now drops 0.32V (that's
0.08 * 4), which is about 3% of the 12V supply voltage - enough to make the lamps run a little dimmer (and last longer) - make the cable 3 times as long (6m) and you'd lose just about 10% of the 12V supply, at which point your lamps are *notably* dim.
To a first approximation, ignore transformer losses and just divide the total wattage of your 6 lamps by 240. So, if they're ditzy little 20W jobs, you'll pull 120/240 = 0.5A; if they're 50W brutes, you'll pull
300/240 = 1.25A. Both values likely to be OK on your existing lighting circuit. Actual transformer losses shouldn't be more than 15%, so we're not doing anything irresponsible by approximating them as perfectly efficient.
All depends on your showering style, I suppose! The Regs require only IPx4 in Zones 1 and 2 - that's roughly 'in the shower cubicle' and 'within 2 foot of it horizontally and two-and-n-alf above it'; but overriding that is good sense and 'suitable for location'. Me, I'd definitely not put anything short of IPx5 where showerspray realistically reaches (the defintion of IPx4 is 'proof against spray of water from all sides', while x5 is 'proof against jets' (of water, not RAF fighters ;-) - and given silly specmanship I'd rather slightly overspec. (Personally I'd not arse about with lights directly *in* a shower cubicle anyway, but people do have the most idiosyncratic wishes when it comes to bathrooms).
But in the ceiling above a shower cubie, I find it hard to argue for anything over an IPx4 rating. Still, we can each choose to exceed minimum standards to whatever degree we prefer.
Superb and thanks Stefek, need to grab a coffee and digest this one. I will probably go for IP65 seeing as I have 4 body jets and they are pretty serious so there could be a chance of spray. I'll experiment before installing.
The Webcam is not a bad idea, I could do with some extra money, I'll send you the link when I get it all rigged up then you can watch me electrocute myself live on the web!!! :)
Been doing some searching for transformers and I see you can purchase multi outlet ones. I'm assuming here that I could in my scenario purchase a 6 multi outlet transformer and wire each LV Lamp to each outlet?
If I were to go for one of your ideas which was to purchase 2 tranformers connect these into the mains and then run 3 LV lamps from each, how would I wire the 3 lamps to each transformer, would I daisy chain the lamps to each other or could I star wire from the transformer?
Yes, but like I said, keep each LV wire short, preferably under 1m and definitely no longer than 2m - for reasons of voltage loss (as mentioned before) and also stability of electronic 'transformers' (some get all unstable when their output wires are long). And keep the LV cable thick, too!
Star wiring is definitely better on the LV side - daisy-chaining means the first run of wire is carrying current to all 3 lamps, so losses in that bit of wire are higher and it'll run warmer.
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