SIRIUS coupling relay for auxiliary circuits
The Siemens 3RH2122-2WB40 is a SIRIUS coupling relay designed for switching auxiliary circuits — the kind of signal-level or control load that follows a contactor or PLC output in a panel. Its 24 V DC coil draws a closing power of 1.6 W, so it sits lightly on a 24 V supply without requiring a separate power supply derating.
The size S00 footprint — 45 mm wide, 73 mm deep, 70 mm high — fits the compact slot in a SIRIUS contactor assembly or standalone on a DIN rail.
Switching ratings and surge suppression
The relay carries a built-in varistor surge suppressor across the coil, so no external snubber is needed for inductive loads switched by the coil circuit. Rated operational currents at various voltages: 10 A at 24 V, 10 A at 230 V, 3 A at 400 V, 2 A at 500 V, 1 A at 690 V — the curve drops with voltage, as expected for an AC-rated auxiliary contact block. At DC voltages, the 24 V rating is 10 A, 60 V is 4.7 A, 110 V is 3 A, 220 V is 1.2 A, 440 V is 0.5 A, 600 V is 0.26 A. Mechanical life is typical 30 million operations.