What it is and what it does
The Siemens 3RH1122-2KF80 is a SIRIUS coupling relay designed for switching auxiliary circuits in control panels — think interposing between a PLC output and a motor contactor coil, or isolating signal circuits. It carries a rated value of 100 V and switches 10 A at 24 V, 6 A at 230 V, and 1 A at 690 V, so it handles both low-voltage DC and higher-voltage AC auxiliary loads without derating surprises. The built-in varistor surge suppressor clips voltage spikes from the coil when it de-energizes — that means less noise coupled into nearby 24 VDC control wiring and longer contact life on the PLC output driving it.
Mounting and integration
Size S00 (45 mm wide, 60 mm tall, 73 mm deep) fits the standard Siemens S00 contactor footprint. Fastening is screw and snap-on mounting. IP20 on the front means finger-safe from the panel face but not washdown-rated — keep it inside a closed cabinet. The screw terminals accept 2x 0.25 to 2.5 mm² solid or stranded wire, standard for control wiring.
Key ratings and what they mean
The 10 A at 24 V rating covers most 24 VDC auxiliary loads — PLC output modules, small contactor coils, indicator lamps. At 230 V it still carries 6 A, enough for a bank of contactor coils or a small motor starter pilot circuit. The 1 A at 690 V is useful for isolating higher-voltage control circuits in 400/690 V panels. Contact reliability is rated at one incorrect switching operation per 100 million operations at 17 V, 1 mA — that's dry-circuit performance for low-level signals, not just power switching. Mechanical life is 30 million operations typical. Shock resistance is 10g/5 ms and 5g/10 ms, fine for industrial panels on machine frames. Surge voltage resistance rated at 6 kV and pollution degree 3 means it's designed for industrial environments with conductive dust or occasional condensation — not just clean control rooms.