With the exception of couplers KBT16 BV-NS/... and KST 16 BV-NS/..., all connectors the series ...-NS and ...-N can be equipped with a microswitch to show the state of the plug-in connection. The microswitch is a changeover switch with 3 flat connecting, tabs 2,8 x 0,5 and a switching capacity of 6A, 250VAC. The microswitch switches immediately prior to the interlock engagement indicating that the plug connection is made.