How do I calculate the Watts used by some domestic lighting?

[Will__]

I have 4 lights that I use to light a row of bookshelves. They're 10 W halogen lamps, and each has its own big chunky black transformer as a plug. Currently, they're all plugged into a standard 13 amp 4 way extension strip. I want to re-route the cable run to situate a new bank of switches in a different part of the room. How do I calculate the Amperage tolerance of the extension cable I can use? They're unearthed units (the black transformers) and thus I only need a two core cable, that much is obvious, but I need to work out whether or not I can get away with using 3 amp cable, which of course is preferable because it's the smallest and most discreet. The black transformers have written on them: Pri: 230V - 50 Hz Sec: 12V - 834 mA which seems pretty obvious to assume means that that's the transform specifics, but is it safe to put 4 of them on a 3 Amp cable? Many thanks. Will

[mattie]

You would need to use the formula P (power) = I (current) x V (volts) measured in Watts If P =IV then I =P/V. This would give the current for the circuit and would give you the fuse rating required. You would have to ensure that you are using the correct units, e.g mA would have to be converted into Amps first, 834mA = 0.834A

[bhg481]

If you had 23 lamps the total power would be 230watts and would draw 1 amp at 230volts.

You could drive 69 x 10watt lamps with 3amp cable.

Your 3amp cable is very adequate for the job.