Electronic Circuits and Projects Forum

Yes, you would wire the lamps in parallel. The current would be as you figured about 13 amps. Here in the US I would use AWG 12 wire (copper) which is about 2.05mm diameter wire. That should handle about 20 amps so it leaves a nice cushion. The only problem I see is the dimmer. You are looking at a dimmer capable of handling over 3 KW. Did you plan on building or buying the dimmer? Also, if this is an outdoor sign I would consider a GFCI line.

Ron

UK ring-main cable (2.5mm^2) is rated at 20A. 15A flexible extension cable is also available but may run a bit warm. UK lighting cable (1.5mm^2) is ok for 10A so would do for spurs.

Deleted

Thanks Alec for the UK cable info. I am really poor when away from AWG.

Also, for the spurs as Alec states will do just fine.

Ron

3kW = ~ 13A (for 230V mains). A properly wired standard UK ring-main wall socket compliant with IEEE Regs is rated to take that, but poor wiring or tarnished contacts could result in the socket and plug heating up over a prolonged period. It would be better/safer to divide your lighting array into two roughly equal parts powered from two different sockets.

That depends on how the outlet is wired and the load it can support as well as the line circuit breaker. Hopefully Alec will be back with info on UK mains outlets.

<EDIT> As I type Alec post! </EDIT>

Ron

I would suggest that you split the lights into groups of 10 - 20, and fuse each group with a 3 A fuse. I would use a few domestic switch fuse units, such as http://www.screwfix.com/p/volex-13a-sw-dp-fcu/98744

That way, after the fuses, you can use 1 mm^2 cable (or even 0.5 mm^2 flex) which are a lot easier to wire into lamps. You are going to want to connect two cables into most of the lamp holders, (one cable from the supply, one to carry on to the next lamp holder) and two larger cables would be more difficult to get into the holders.

By the time you have wired 119 lamp holders, you will appreciate the advantage of a thinner cable. You will have to strip off nearly 500 wire ends.

The smaller fuses will also mean that a shorted bulb will be far easier to find and there will be a less impressive bang if something goes wrong.

As a rule, you should always have cables rated up to the fuse value that is feeding them, so if you don't have smaller fuses, your cables should be able to take the full 13A of the plug fuse, and if there is a fault the fuse should blow before the cable is damaged. I realise that a 13 A fuse feeding a 1.5 mm^2 cable is fine, but you shouldn't drop sizes down further without smaller fuses.