What this part is and what it does
The Siemens 3RH2122-1BF40-ZX95 is a Size S00 contactor relay with a 110 V DC coil, designed for screw and snap-on mounting onto a standard 35 mm DIN rail. Its primary job is switching control circuits in panels — think PLC outputs driving motor contactor coils or signaling to downstream auxiliaries. The 110 V DC coil pull-in and hold power are both 4 W, so the control transformer or power supply needs to budget for that steady-state draw.
Switching capacity — what the DC ratings mean for fit
This relay carries a set of DC-12 switching ratings that define the load it can break across different voltages. At 24 V DC it is rated for 10 A; at 110 V DC that drops to 3 A; at 220 V DC it is 1.2 A; and at 600 V DC it falls to 0.26 A. The arcing time is 10 to 15 ms, and the minimum switching current spec (at DC 7 to 13 ms) tells you the relay can handle low-energy signals without contact wetting issues. For a maintenance planner, the 24 V DC 10 A rating is the one that covers most PLC output interposing and solenoid valve circuits — that is the fast-moving spare to keep on the shelf.
Mounting and integration
Mounts via screw or snaps onto 35 mm DIN rail. The mounting position is flexible — ±180° rotation on a vertical surface, and it can tilt forward/backward by ±22.5°. Clearances: 10 mm upward, 10 mm forward, 10 mm downward, 6 mm at the side. The Size S00 body is 45 mm wide, 58 mm high, and 73 mm deep — fits standard panel layouts without special bracketry. Wire termination accepts 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or 2x 4 mm² solid or stranded.
Environmental and compliance
Operates in -25 to +60 °C ambient; stores in -55 to +80 °C. Pollution degree 3 (industrial environment with conductive pollution). Relative humidity minimum 10 %. RoHS compliance date for substance prohibitance is 10/01/2009. Surge voltage resistance rated at 6 kV.