What it is and what it does
The Siemens SIRIUS 3RH1911-1LA20 is an auxiliary switch block that adds two normally-open (NO) contacts to a size S00 contactor or contactor relay. It snaps onto the front of the contactor without tools — no extra DIN rail space needed, just a firm push until the latch clicks. Switching capacity depends on the circuit voltage: rated for 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V. At 690 V in AC-15 duty it handles 1 A. That covers pilot-duty control circuits, PLC outputs, and signal isolation up to the contactor's rated insulation voltage of 690 V.
Physical fit and wiring
Dimensions: 36.5 mm wide, 37.5 mm tall, 41.5 mm deep — compact enough to fit inside a shallow gland plate or behind a panel door without crowding adjacent devices. The snap-on mount engages the contactor's front profile, so the contactor's own DIN-rail footprint stays unchanged. Terminals are screw-type, accepting 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) with core-end processing, or the AWG equivalents 2x (20 to 16) and 2x (18 to 14). Strip length and torque follow standard Siemens S00 practice — no special tooling needed.
Contact reliability and service life
Rated for 10 million mechanical switching cycles typical. Contact reliability is specified as one incorrect switching per 100 million operations at 17 V, 5 mA — that matters for low-energy signal circuits where oxide films on dry contacts can cause intermittent faults. The same reliability spec applies at 1 mA for the auxiliary contacts, so it handles PLC-level signals without the usual wetting-current worry.
Environmental and protection
IP20 on the front — fine inside a closed control cabinet, not for washdown or outdoor exposure. Operating temperature range from -25 °C to +60 °C; storage from -55 °C to +80 °C. Surge voltage resistance rated at 6 kV, which is standard for industrial control circuits running alongside contactors and drives.