What it is and what it does
The Siemens SIRIUS 3RH2911-1GA31-ZW98 is an auxiliary switch block that mounts on the front of a contactor relay. It gives you 3 normally-open and 1 normally-closed contact set (3 NO + 1 NC), wired to screw terminals. The contacts are physically coded so they only fit with 3RH2140 and 3RH2440 contactor relays per EN 50011 — no guessing if it'll line up on the wrong base. Rated for a maximum of 10 A, this switch handles control-circuit loads across a range of voltages. At 24 V it's rated 6 A, at 110 V it's 1 A, and at 400 V it's 3 A. The insulation voltage is 690 V with pollution degree 3, so it's solid for standard industrial panel environments. Snap-on mounting onto the contactor relay keeps installation quick — no tools needed beyond a screwdriver for the screw terminals. The IP20 front protection means it's fine inside a closed cabinet; keep it out of washdown zones.
Key ratings and what they mean
The AC-15 rating at 690 V is 1 A. AC-15 covers electromagnetic loads like contactor coils, so this switch can reliably break that inductive kick without welding contacts. Mechanical service life is 10 million switching cycles typical. That's a lot of operations — for a machine that cycles once every 10 seconds, that's over three years of continuous duty before the mechanism wears out. Contact reliability is 1 faulty switching per 100 million operations at 17 V, 1 mA. That's important for PLC-level signals where a dry circuit might not burn through oxide — this switch handles low-energy logic reliably.
Integration notes
The screw terminals accept 2x (0.5... 1.5 mm²) or 2x (0.75... 2.5 mm²) with core end processing, or AWG 20-16 and 18-14. Strip length and ferrule sizing follow standard practice for the terminal class. Dimensions are 36 mm wide, 37.5 mm high, 43.7 mm deep. That 36 mm width matches the standard SIRIUS contactor relay footprint — it doesn't add extra DIN rail space beyond the base relay. Operating temperature range is -25 to +60 °C, storage from -55 to +80 °C. Fine for most indoor panels; if the cabinet sees direct sun or a heat source, check the ambient stays under 60 °C.