Switch live at switch

Hiya

I'm sure this had been answered before but cannot find it.

I'm fitting a new light switch, but both wires are red. I cannot remember which was the live and which was switch live (and no indication which is which) . Is there a way of testing with a multimeter?

Cheers in advance

Martin

 

It really doesn't matter. The switch just joins them together.

 

Measure the voltage between earth and each red with the light switched off. If there is no earth at the switch use a long wire to find earth (or neutral) from somewhere else. Simplest way should be an extension lead.

Unless you are making some changes You shouldn't need to know which is which anyway.

 

You can also do a safer continuity check , if its on a mcb not an Rcbo, between each cable to earth with the power OFF and ALL other light switches off, the live should be open circuit and the switch live closed circuit, you can possibly double check further by removing the relevant bulbs, in the room and the switch live will then also be open circuit.
As said above if its 1 way 1 gang its not important , they may have been connected anyway round previously.

 

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