The Siemens SIRIUS 3RH1921-1MA02 is an auxiliary switch block with 2 NC contacts, designed to snap onto 3RT1 contactors and contactor relays. It uses screw-type terminals and is rated for a maximum of 10 A, with specific current ratings that vary by voltage — 6 A at 24 V, 6 A at 125 V, 6 A at 230 V, 6 A at 250 V, 3 A at 400 V, and 0.3 A at 220 V, among others. The block measures 51 mm deep, 44 mm wide, and 38 mm high, and carries an IP20 protection rating on the front.
Mounting and Integration
Snap-on mounting directly onto the 3RT1 contactor or contactor relay — no DIN rail needed, no extra hardware. The screw terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) with core end processing, or 2x (20 to 16) and 2x (18 to 14) AWG. The block adds 51 mm of depth to the contactor assembly, so check enclosure clearance if retrofitting into a tight panel.
Contact Ratings and Reliability
The 2 NC contacts are rated for AC-15 duty at 690 V at 1 A. Contact reliability is specified at 1 faulty switching per 100 million operations at 17 V and 1 mA — a strong figure for low-energy signal switching in PLC or safety circuits. Mechanical service life is typical 10 million switching cycles. The insulation voltage is 690 V AC at pollution degree 3, with a surge voltage resistance of 6 kV.