DIY Doctor UK DIY Forums

HELP
I've just bought a timer switch for my immersion heater.The instructions say connect the live from the SUPPLY to terminal 2 and the live from the HEATER to terminal 1 . Neutral wire is not a problem as both go to terminal 3. Earth is not a problem either.

When I take my old on/off switch off the wall how do I know which live is supply and which is to the heater.

I am sure I will get told off for saying this but here goes.
If its electronic timed and uses a battery than Line in and Line out being swapped will not normally make any difference. There are spark catchers that may not work as well as they should and normally the moving contact is always the out contact but in real terms they still work.
Where the timer is driven by the power in then if selected off and wrong way around the clock will not work so simple to remove again and swap.
But do insure turned off to test as if turned on it will still work until off is reached and because it loses power while trying to turn off it may arc and damage unit.
Of course we would use a meter and test but I will assume you don't have that option.
Eric

b4 removing anything switch off the timer and use a volt stick to pick up the current flow in the supply cable .. use this method rather than mucking around with 2nd guessing manufacturers instructions. then isolate the circuit and crack on.