What it is and what it fits
The Siemens 3RH2911-2HA12-0KT0 is a front-mounted auxiliary switch block in the SIRIUS family, designed to snap onto 3RT2 power contactors and 3RH2 contactor relays. It carries one normally-open and two normally-closed auxiliary contacts, wired out to terminals 21/22, 31/32, and 43/44 — the fourth position is unpopulated. The spring-loaded terminals accept 2x (0.5 to 2.5 mm²) without ferrule, or 2x (0.5 to 1.5 mm²) with core-end processing, and also take 2x (20 to 14 AWG) stranded.
What the ratings mean for the panel
The headline rating is 10 A at 24 V, which is the maximum continuous current the contacts can carry in a control circuit. For inductive loads in AC-15 duty, the rated operational current drops to 1 A at 690 V — that's the figure that governs switching of contactor coils and solenoid valves at higher voltages. The contact reliability spec — one faulty switching per 100 million operations at 17 V, 1 mA — means this block is trustworthy for PLC-level dry circuits, not just power switching. Mechanical life is 10 million switching cycles typical, so it outlasts most contactor bodies it rides on.
Mounting and integration
Snap-on mounting to the front of the contactor or relay — no tools needed, no DIN rail footprint consumed beyond the base device. The block adds 36 mm width and 47.7 mm depth to the assembly, with a height of 41.5 mm. IP20 on the front means it's protected against finger contact but not washdown; keep it inside the enclosure. Operating temperature range is -25 to +60 °C, storage from -55 to +80 °C. Surge voltage resistance is rated at 6 kV, and insulation voltage at 690 V AC with pollution degree 3 — standard for industrial control panels.