This Siemens SIRIUS 3RH2911-2NN22-0MC0 is a front-mounted auxiliary switch block built for contactor relays and power contactors. It gives you 2 NO plus 2 NC contacts, with two of those NO contacts rated as solid-state compatible — meaning they handle the low-voltage, low-current switching that PLC outputs and solid-state relays need without the contact reliability issues you get with standard silver contacts. The contact reliability spec backs that up: one incorrect switching operation per 100 million operations at 5 V and 1 mA.
Snap-on fit and spring terminals
It snaps onto the front of specific 3RT102 and 3RT103 contactor sizes using the listed adapter kits — 3RT2926-4NA00 for the 3RT102 frame, 3RT2936-4NA00 for the 3RT103 frame. Width is 36 mm, depth 47.7 mm, so it adds minimal real estate to the contactor face. Spring-loaded terminals accept 2x (0.5 to 2.5 mm²) stranded without ferrules, or 2x (0.5 to 1.5 mm²) with core-end processing. AWG range is 2x (20 to 14). That spring cage saves panel-build time versus screw terminals — no torquing, no re-torquing on commissioning.
Ratings for a real panel
Mechanical service life is 5 million switching cycles, typical for an auxiliary block that isn't carrying main motor current. Front protection is IP20 — finger-safe, but keep it inside the enclosure.