The Siemens 3RH1921-2CA10-ZX95 is a front-side auxiliary switch block from the SIRIUS family, designed to snap onto 3RT1 contactors. It adds one normally-open (NO) contact for feedback or control logic, wired via spring-loaded terminals that accept 2x (0.5…2.5 mm²) stranded or 2x (20…14 AWG) solid conductors. Rated for 10 A maximum, with a switching curve that drops as voltage rises — 6 A at 24 V, 3 A at 400 V, 0.26 A at 600 V — so it handles both 24 VDC control circuits and higher-voltage signal switching within the same block. The AC-15 rating at 690 V is 1 A, covering inductive pilot-duty loads.
Snap-on mounting clips directly to the front of a 3RT1 contactor — no tools needed. Dimensions are 10 mm wide, 38 mm tall, 51 mm deep, so it adds minimal width to the contactor stack. Spring-loaded terminals (cage-clamp style) accept up to 2x 1.5 mm² with ferrules or 2x 2.5 mm² bare stranded. Strip length is standard 8–10 mm. No screw torque to check — just push the spring, insert, release.
The 10 A maximum is the thermal continuous current (Ith). The real-world switching capacity depends on voltage and load type: at 24 V it switches 6 A (resistive) or 10 A (rated value for the 24 V DC coil circuit). For AC-15 pilot duty at 690 V, it's rated 1 A — enough for a contactor coil or small solenoid. Mechanical life is 10 million cycles typical, so it outlasts most contactors it rides on. That covers industrial panel environments with moderate contamination (dust, non-condensing humidity).