Tronics Intermediate switch

An intermediate switch is used when you have three or more light switches controlling one light.

The middle switch, or switches, need to be an intermediate switch for the lighting circuit to work correctly.

The typical example of this is on a landing in a house, when perhaps there is a switch at the bottom of the stairs, one at the top of the stairs and one at the end of the landing. On this circuit you would need the middle switch; the one at the top of the stairs, to be an intermediate switch. The other two light switches would need to be two way switches.  

This can be continued for multiple switches, so it applies to three or more switches.