What it is and where it fits
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.
Mounting and panel fit
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. IP20 on the front face means it's protected against finger contact inside a closed panel. 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.
What the ratings mean for the buyer
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. Contact reliability is specified as 1 faulty switching per 100 million operations at 17 V, 1 mA — meaning it's reliable even for dry-contact PLC inputs or low-energy signal circuits. Mechanical life is 10 million cycles typical, so it outlasts most contactors it rides on. Surge voltage resistance is 6 kV, and insulation voltage is 690 V AC at pollution degree 3. That covers industrial panel environments with moderate contamination (dust, non-condensing humidity).