The Siemens 3RH6140-1KF40 is a SIRIUS coupling relay — a DC-operated auxiliary contactor in the S00 frame, designed to switch control and signal circuits rather than motor loads. Its 4 normally-open contacts give you four independent switching paths, each rated 6 A at 24 VDC (AC-12) and 10 A at 230 VAC. The 6 kV surge voltage resistance means the relay handles transient spikes common in industrial panels without flashover — a real concern when the contactor sits near drives or switching power supplies. The coil is 110 VDC, pulling 2.8 W during both closing and holding. A built-in suppressor diode clips the inductive kick when the coil de-energizes.
Mounting and wiring — panel-builder notes
Snaps onto 35 mm mounting rail with a screw-down clamp. The S00 footprint is 45 mm wide, 57.5 mm tall, 73 mm deep. Screw-type terminals accept 2x (0.5...1.5 mm²), 2x (0.75...2.5 mm²), or 2x 4 mm² solid/stranded wire. For finely stranded wire with ferrules, the range is 2x (0.5...1.5 mm²) and 2x (0.75...2.5 mm²).
Contact reliability and switching frequency
That's the dry-circuit threshold — it tells you the silver-alloy contacts are gold-flashed or otherwise treated to switch low-energy signals (PLC inputs, status lamps) without oxidation failures. Mechanical life is 30 million cycles typical. Maximum switching frequency is 10,000 operations per hour for both AC and DC loads, dropping to 1,000 per hour under DC-12 and DC-13 duty — the inductive DC loads heat the contacts faster.