What it is and what it does
The Siemens 3RH1122-1BB40-ZW96 is a SIRIUS auxiliary contactor — a compact relay block used to switch control signals, pilot lamps, and logic-level loads in a motor starter or contactor assembly. It carries a 24 VDC coil and is rated for 10 A in AC-12 duty (resistive loads at line voltage), so it handles typical control-circuit switching without derating. The contact arrangement is 2 normally-open and 2 normally-closed instantaneous contacts, with no leading, lagging, or make-before-break options — a straightforward 2+2 configuration for standard interlocking or status feedback. It mounts on a DIN rail via the integrated clip (screw and snap-on) and fits the S00 contactor footprint — the same width as the 3RT2 series contactors in that frame size. The front face carries IP20 protection, so it's suited for enclosed panels where accidental finger contact is the only exposure.
Key ratings and what they mean for fit
The 24 VDC coil draws 3.2 W during both pick-up and hold — no inrush spike to stress a DC supply, but the steady-state draw is constant, so budget that wattage in your 24 VDC bus calculation. The coil is rated for continuous duty across the full operating temperature range of -25 to +60 °C. Switching capacity varies by voltage: at 110 V it's rated 1 A, at 230 V it's 6 A, and at 400 V it drops to 3 A. The 10 A AC-12 rating is the maximum at 24 V rated value — for higher voltages the contacts derate significantly, so verify against your actual load voltage, not just the coil voltage. Contact reliability is specified as one incorrect switching operation per 100 million at 17 V, 1 mA — this is a dry-circuit rating, meaning the contacts are reliable even at low signal levels without needing a minimum wetting current. Pollution degree 3 (industrial environment) and surge voltage resistance of 6 kV confirm it's built for panel-level transients.
Mounting and wiring
The 45 mm width and 57.5 mm height fit the standard S00 slot on a DIN rail. Depth is 72 mm, which includes the coil terminals — account for that when spacing the panel door or adjacent components. The mounting position is flexible: it can be rotated ±180° on a vertical surface and tilted forward/backward ±22.5°, so it fits tight layouts without derating. Terminals accept solid conductors: 2x 0.5–1.5 mm², 2x 0.75–2.5 mm², or 2x 4 mm². That covers most control wiring sizes; for 4 mm² you'll need a ferrule or direct insertion. The screw-clamp design is standard for the SIRIUS family.