Answer to lights question below

[sddsddean]

I can't scroll down to the 'submit' button, on the answer page, so I'll put the answer here. You have 4 x 10W which is 40W. Power (W)= Volts x Amps. So you have 12 x 3=36W available. So you will blow the fuse, or worse, set fire to the cable. If you get 5 amp cable, this will allow you 60W so you will only be loading the cable to 60% of its capacity.

[Hippy]

The original question said that the units are 10W halogen, and that the secondary of the transformers are 12v and 834mA. As Watts = Volts x Amps then 12 x 0.834 = 10.008 and there is your 10 Watts. However, the cable to the primary is at the higher pressure of 240 Volts. Now, the same current (834mA) will flow in this circuit with the addition of some transformer inefficiencies (heat and magnetic leakage) say 20% to be really gloomy. So the current required at the primary will be 834mA + 167mA = 1A. Now, as there will be three of these units drawing current then the maximum loading on the mains will be 3 Amps which calculates back to 3 x 240 = 720 Watts.

The 3 Amp cable should be fine, provided that the insulation is rated for high voltages and is double (each wire is enclosed in PVC and the whole is within a second PVC sheath, and that the cable is not squeezed by clips, passing through holes, or tight bends. Keep the radius of the bends to more than eight times the diameter of the cable.

[Hippy]

I just noticed that I missed the point that Will proposed four such lamps and not three. In this case, 3 Amp cable will not suffice. Please disregard my advice for same above in final paragraph. My solution here would be to use the 3 A cable but use two runs with two lamps connected to each, or a ring with three amp cable so that you can double the capacity of the cable as the current is shared through the ring.

[sddsddean]

OOps! Forgot about the secondary coil on the transformer. I'll go along with Hippy's answer; use 5 amp to be on the safe side.

[Will__]

Thanks for that, guys. Very helpful: to confirm, either I use 2 cable runs of 3 Amps, or one of 5 ? I have to go through, under and behind the bookshelves for neatness and switch location, so there will be a few 90 degree bends and several cable clips (correct size). If I do this with 5 amp 2 core (each eclosed in plastic, with a plastic exteriror covering them both), then I shouldn't burn the house down? Many thanks. Will ps Am slightly lost on the whole 'ring with 3 amp cable' part....beyond me, I'm afraid.

[Hippy]

Yes, the 5A solution will be fine. Try not to nip the cable too much.