The Siemens 3RH1911-1FB11-ZW96 is an auxiliary switch block designed for contactor relays and contactors used for switching motors, Size S00. It provides one normally-open (NO) and one normally-closed (NC) contact, wired via screw terminals, and mounts to the front of the contactor relay. The 1U designation means the switching function follows DIN EN50005 contact arrangement, so it slots into the standard auxiliary contact position on the relay without modifying the wiring scheme.
This block snaps onto Size S00 Siemens contactor relays (3RH11/3RH12 series) and 3RT1 contactors in the same frame size. The screw terminals accept standard control wiring, and the block occupies the front auxiliary slot, adding two extra contacts to the relay without increasing the DIN-rail footprint. For a panel builder, that means you can add feedback or interlock signals without re-laying out the enclosure.