Can i fit a switch

[mrffl123]

On my electrick swicth it takes 2 wires on the circuit i want to fit it to it has 3 wires incl the comm wire can i fit?????

[stanleyman]

If two wires in the circuit and three terminals on the switch then yes, just use the common and one other depending on the on/off position.

If three wires in the circuit and two terminals on the switch then yes only if it is not a two way lighting circuit.

[qapmoc]

This does seem to be a simple question of maths - 3 into 2 won't go.
If the existing switch is in a circuit where you can switch on/off one light with two different switches, for example at the top and bottom of the stairs then it is a two way switch and you must get another two way switch which will have three terminals.