What This Auxiliary Switch Block Does
The Siemens 3RH2921-2DE11 is a lateral-mount auxiliary switch block for the SIRIUS 3RT2 contactor and 3RH2 contactor relay family. It provides one normally-open and one normally-closed instantaneous contact, with the NO on the left side (terminals 51/52, 63/64) and the NC on the right side (terminals 33/34, 41/42). The contacts are rated for solid-state loads, meaning the switching reliability at low signal levels is specified: one incorrect switching operation per 100 million operations at 5 V and 1 mA. That makes this block suitable for directly switching PLC-level signals or solid-state inputs without a separate interface relay.
Snap-on mounting attaches directly to the left or right side of a 3RT2 contactor or 3RH2 contactor relay — no tools, no DIN-rail space consumed. The block is 10 mm wide, 66 mm deep, and 61.2 mm high, so it adds minimal width to the contactor stack. Spring-loaded terminals accept 2x (0.5 to 1.5 mm²) with ferrule or 2x (0.5 to 2.5 mm²) without; AWG equivalent is 2x (20 to 14). No screwdriver needed for termination, which speeds panel wiring.