Wiring a surface mounted timer switch

[lyntwyn]

I purchased a surface mounted timer for my immersion heater which will fit a standard 32mm deep socket box, so it seemed a very easy task to replace the standard on/off switch with it. In theory it is a simple job but I only have L,N & E going into existing switch whereas the instructions for new timer switch ramble on about live/neutral output to appliance etc. The immersion has a dedicated fused power supply. Presumably I only need to connect the E cable to the box terminal and the L & N to the relative blocks on the timer. But which ones are the relative terminals? I suspect that I simply connect the L & N to blocks 3 &4, BUT what bothers me is that the cables wired into both of these is blue whereas blocks 1 & 2 are wired red! Timer spec link below, any guidance much appreciated.


http://www.greenbrook.co.uk/pdf/T69.pdf

 

[viewer]

In your existing switch you must have L/N/E in and out - assuming it was connected and working. Don't work on wire colours; the mains in should be conventional, but within the timer you need to follow the routes. Should be straight forward. L 3 & N 4 in (i.e. feed from mains) as shown on right hand side. N4 continues to appliance. Link 3-2 is made and L1 to appliance goes out from left hand side (in diagram). Ensure all earth paths continuous; the timer itself doesn't need an earth, but the appliance and any metal boxes (etc) do. HTH

 

[TicklyT]

If you've only got 2 wires + earth at the switch, the chances are you will have a problem, as the wires will be a live and a switched live that has not been sleeved red or brown.

The time switch requires a live, a switched live and a neutral to operate, and an earth for your safety.

Electricity doesn't care what colour sleeving is round a conductor, but it is very remiss of whoever wired your old switch not to sleeve the switched live, so anyone else can tell what's going on.

You may still be able to use your time switch, either in a different place, or by running additional wiring to the place you intend to fit it.

 

[lyntwyn]

Thanks both.
TicklyT, the three wires are sleeved, for L N & E. This is a newish property so wiring is likely to be untouched from original.

viewer, yes thats what I thought. Currently E is wired into the switch socket but I will move to the terminal on the box.

I think I'm correct in believing that replacing the switch with a timer does not require a certificate under the 2006 Regs.

Thanks again.