The Siemens 3RH2911-1AA01-ZX90 is a front-mounted auxiliary switch block carrying one normally-closed (NC) contact, wired through screw terminals with cable entry from the top. It snaps onto SIRIUS 3RT2 contactors and 3RH2 contactor relays — the "with 3RH2" note on the line means this variant is specifically packaged and tested for that relay family, though the mounting interface is shared across the 3RT2/3RH2 platform. Rated for a maximum of 10 A, with the AC-15 utilization category carrying 1 A at 690 V. The mechanical service life is rated at 10 million switching cycles, and contact reliability is specified at 1 faulty switching per 100 million operations at 17 V, 1 mA — a figure that matters for PLC-level signal integrity in low-energy circuits.
The 10 A maximum is the thermal current (Ith) — the continuous carry capacity through the closed contact. The real switching limits depend on voltage and load type: at 24 V DC the contact handles 6 A, at 60 V DC it drops to 2 A, and at 220 V DC it's only 0.3 A. For AC loads the AC-15 rating at 690 V is 1 A — that's the inductive solenoid/contactor coil switching duty. The insulation coordination is rated for 690 V AC with pollution degree 3, and surge voltage resistance is 6 kV. That puts it in the standard industrial control panel range — no special derating needed for most 400 V or 480 V environments, but verify if your panel sees repeated surges above 6 kV.
Snap-on mounting to the front of the contactor or relay — no tools, no DIN rail footprint consumed. The auxiliary switch adds 23.6 mm width, 27.5 mm height, and 38.6 mm depth to the assembly. Screw terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) with core end processing, or 2x (20 to 16 AWG) or 2x (18 to 14 AWG) for stranded wire.