The Siemens 3RH2140-1AH00 is a SIRIUS auxiliary contactor in the S00 frame size, carrying 4 normally-open instantaneous contacts. It's designed for switching control circuits, signal interlocking, and extending the contact set of a main contactor or a PLC output — the 4 NO configuration gives you four independent isolated contacts that close when the coil picks up. The 24 V AC coil (50/60 Hz, 0.8...1.1 × Us) pulls in reliably down to about 19 V and drops out below 17 V — consistent with the SIRIUS family's standard tolerance. Pickup time is 4 to 15 ms; arcing clears in 10 to 15 ms. That's fast enough for most control logic, but if you're sequencing safety-rated contacts you'll want to account for the ±5 ms spread in your scan budget.
Contact ratings are given per IEC/EN 60947-5-1: 10 A at 24 V AC, 3 A at 110 V, 1.2 A at 220 V, and 1 A at 690 V. The 10 A at 24 V rating is the resistive load limit for low-voltage DC control; if you're switching inductive loads (small relays, solenoid valves), derate by about 40% or add a free-wheeling diode. Electrical life depends on the load.
The S00 footprint is 45 mm wide × 57.5 mm high × 73 mm deep. Terminals accept 2 × (0.5...1.5 mm²) solid or stranded, 2 × (0.75...2.5 mm²), or a single 4 mm² conductor.
If you're looking at the 3RH2140-1BP40 (same S00 frame, 4 NO, but a 24 V DC coil), the mechanical and contact ratings are identical — the only difference is the coil supply. The 3RH2140-1AH00 with its AC coil will not drop into a panel wired for DC coil control without changing the coil supply circuit. For AC control panels, this is the correct fit.