What this relay is and where it lands
The Siemens 3RH1122-2WB40 is a SIRIUS coupling relay, size S00, designed to switch auxiliary circuits in control panels. It carries a 24 V DC coil and is rated for 10 A at 24 V — enough for pilot duty, signal isolation, or interposing between a PLC output and a higher-power contactor coil.
Mounting and integration
Snaps onto a DIN rail or screws directly to a backplate — the fastening method covers both panel-build styles. The 45 mm width matches the S00 footprint.
Switching capability and contact reliability
Two instantaneous contacts (NO/NC configurable per the wiring diagram) handle the auxiliary switching. The relay is rated for 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, 2 A at 500 V, and 1 A at 690 V — derate as voltage climbs. Contact reliability is specified as one incorrect switching operation per 100 million operations at 17 V, 1 mA, which means it can handle dry (low-energy) signal switching without contact-film problems. Mechanical life is 30 million operations typical.
Environmental and electrical robustness
IP20 on the front keeps fingers and tools out — standard for panel-mount gear. Pollution degree 3 means it tolerates conductive dust and humidity typical of industrial environments. The coil draws 1.4 W closing and holding (DC), so no thermal derating headache in a dense row. Surge voltage resistance is 6 kV, giving a solid margin for transient spikes on the control supply. Shock tested to 10g / 5 ms and 5g / 10 ms, and operating temperature spans -25 to +60 °C.
Lifecycle and compliance
Marked as current production — no phase-out or last-time-buy notice on this code. The built-in varistor surge suppressor (across the coil) means you don't need an external flyback diode for DC switching, which simplifies BOM and panel wiring. RoHS compliance date is July 1, 2006, and the part carries Siemens SIRIUS branding with full traceability through the authorized channel.