An intermediate switch is used when you have three switches controlling one light. A typical example of this is on a landing. There is a switch at the bottom of the stairs, one at top of the stairs and one at the end of the landing. On this circuit you would need the middle switch to be intermediate (i.e. the one at the top of the stairs) in order for all the switches to function properly. Made from high quality ultra slim, premium grade material. Complete with integral gasket. Compliant to all relevant British safety standards. Minimum mounting depth: 16mm. Dimensions: 87.5mm x 87.5mm. Supplied in retail blister with full fitting instructions. 15 year guarantee.