# LV lighting questions

Having bought all the necessary stuff for my LV lighting I have two questions after reading the instructions.
1. Is plasterboard/plaster flammable?
2. The transformer instructions state that with the 150w model (the one I have) that the maximum length of the output cables are 0.8m. This is with a cable size of 1.50mm2. If I increased the cable size, say to 2.5mm2, then do I gain some extra length? If so how much?
Thanks,
Bill
--
Aim to work one hour less this week than last week and get paid the same.

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Not in the context of where you can position your lights. Wooden joist are though!

a
do
You should be able to increase the length in the same ratio as the cross-sectional area without increasing the resistance. That would get you up to 1.33 metres.
Does the 0.8 metres assume that all the current for 150w-worth of lights goes down a single cable? If so, you can gain some more length by wiring them in a star formation - using a junction box very close to the transformer.
Roger
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On Wed, 03 Dec 2003 22:06:26 +0000, Roger Mills wrote:

The 1.5 mm2 cable has a conductor resistance at 0C of 0.0104 ohms / metre * 2 for outgoing+return path = 0.0208 ohm/m
So with say, 150W, assuming 12V lamps (are they?), that would be 12.5A. Cable voltage drop would be 0.0208 * 12.5 = 0.26V per meter which at 0.8 m is sod all in terms of it's effect on the lamps.
I suspect you could get away with 2m length (0.5V drop) without imparing the lamps too noticibly, and as the other posters have mentioned, 2.5mm2 cable is going to nearly halve your volt drops, so double again.
I would guess 2.5mm2 is good for 4m give or take even with non star wiring.
You can always try it before installing and see if it looks OK. No danger of overheating cables - the length is not relevant to that problem so I don't see a fire hazard or anything nasty from too long a cable - just dim lights if you overdo it.
Hope that helps
Tim S
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Bill Gardener wrote:

No. I gets very crumbly if you play a plumbers blowtorch on it and heat it to red heat tho.
Paint is fl;ammable tho...

Yes. the resitsance is proportional to length/area, so 0.8x2.5/1.5 would be the same resistance= 1.33m

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