On Wed, 03 Dec 2003 22:06:26 +0000, Roger Mills wrote:

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?


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.


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