In electrical installations with multiple sub-distributions and residual current circuit breakers, an economical central ON-OFF control can be set up with the specially developed switching devices ISK 41, ISK 42. The central control inputs are galvanically isolated from the inputs and outputs of the supply side by optocouplers. This means that, unlike conventional impulse relays with central control, ISK 41 and ISK 42 can be connected between different networks, RCDs or potentials without decoupling relays. ISK 41: 1 NO contact 230V AC 16A, potential-free.