The plugs and sockets in the CES system comply with IEC/EN 60309-1/ -2 (CEE). Contrary to the switch socket, the interlocked switch is integrated in the socket body for the small 16A socket. It has switching capacity AC3 according to IEC 60 947-3. The ability to plug the Ex-plug in non-Ex-sockets is guaranteed, while operation of the Ex-socket using a non-Ex-plug is reliably prevented. The ability to plug Zone 2 plug into a Zone 1-socket is reliably prevented. However a Zone 1 plug can be used with a Zone 2 socket.