A modular circuit arrangement for switching electrical power includes a relay socket, an adapter and a relay. The adapter is detachably connectable to the relay socket and includes a semiconductor relay and a control unit electrically connected to the semiconductor relay. The relay includes a mechanical switch and is electrically and mechanically detachably connectable to the adapter so as to connect the semiconductor relay of the adapter in parallel to the mechanical switch. The control unit is configured to actuate the relay and the semiconductor switch at different times.