What it is and what it does
The Siemens 3RH2122-2LB40-2LA0 is a SIRIUS auxiliary contactor, size S00, designed to switch control circuits in motor starter and contactor assemblies. It carries a 24 VDC coil and is rated for 10 A at 24 V (AC-15 / DC-13 duty), so it handles typical PLC output loads, relay coils, and signal lamps in a control panel.
Mounting and integration
Mounts via screw and snap-on onto standard 35 mm DIN rail. The S00 footprint — 45 mm wide, 70 mm tall, 116 mm deep — fits alongside contactors in the same rail section. Accepts 2 x (0.5 to 4 mm²) solid or stranded wire per terminal. Mounting position is hanging on a horizontal surface, with clearance: 10 mm upwards, 10 mm forwards, 10 mm downwards, 6 mm at the side.
Ratings and performance
Coil closing power is 13 W at DC, with a built-in varistor surge suppressor across the coil — no external flyback diode needed for DC switching. Mechanical life is typical 30 million operations; switching frequency up to 10,000 cycles per hour at AC. Arc time is 10 to 15 ms. The contactor is rated for pollution degree 3 (industrial environment). Ambient operating range -40 to +70 °C; storage -55 to +80 °C.