What it is and what it does
The Siemens 3RH1122-1BN40 is a SIRIUS auxiliary contactor in size S00, designed to switch control circuits and signal loads in a motor starter or contactor assembly. It provides 2 normally open (NO) instantaneous contacts and no normally closed (NC) contacts, rated at 10 A in AC-12 duty (resistive control loads at 24 V). The surge voltage resistance is rated at 6 kV, which means it can handle transient overvoltages typical in industrial control panels without flashover. It mounts via screw or snap-on onto a DIN rail, fitting into the same footprint as the S00 contactor family.
Key ratings and what they mean for fit
The AC-12 rating of 10 A at 24 V is the resistive load capacity for the auxiliary contacts — this governs how many PLC outputs or relay coils you can switch without derating. For inductive loads, the switching capacity drops: at 230 V it's rated 6 A, at 400 V it's 3 A, and at 690 V it's 1 A. The 2 NO contact configuration (with 0 NC) means this unit is a straight make-only block; if your circuit needs a break contact, you'd need a different variant or an add-on block. The coil closing and holding power is 3.2 W DC, a low draw that keeps the control transformer sizing tight. Operating temperature range is -25 to +60 °C, with storage from -55 to +80 °C — adequate for most indoor panel environments but not for direct outdoor exposure without a cabinet.
Where it goes in the panel
This auxiliary contactor is sized for the S00 frame, which means it occupies a 45 mm wide DIN-rail footprint with a depth of 72 mm and height of 57.5 mm. It can be mounted in any orientation: +/-180° rotation on a vertical surface, and tilted forward/backward by +/-22.5°. The screw and snap-on mounting lets you clip it directly onto the DIN rail without tools, or screw-fix it for vibration-prone locations. The IP20 front protection is standard for enclosed panels — no washdown rating, so keep it inside a cabinet. Side clearance of 0 mm means you can gang it next to other devices without spacing.
Wiring and termination
The screw terminals accept solid conductors: 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or 2x 4 mm². This covers most control wiring from signal-level to power-limited circuits. The shock resistance is rated at 10g for 5 ms and 5g for 10 ms, so it holds up in panels mounted on machinery with moderate vibration. Pollution degree 3 means it's suitable for industrial environments with conductive pollution (like dust or light moisture), which is typical for most factory-floor panels.