In electrical installations with several sub-distributors and fault-current protection relays, the pulse switches ISK 41/42 permit low-cost implementation of a central On/Off control. The central control inputs are isolated from the inputs and outputs on the power side and can be controlled with AC or DC voltages of 8-230 V. The ISK 42 has a second potential-free relay contact (10A, normally open) and a central pulse input.