What this contactor is and where it fits
The Siemens 3RT1025-1AH00 is a SIRIUS power contactor in the S0 frame size, with three normally-open main contacts and screw-type terminals. It mounts on a 35 mm DIN rail per EN 50022, using either a screw or snap-on method, so it drops into a standard panel enclosure without special brackets. The 45 mm width and 85 mm height mean it fits alongside other S0 devices in a multi-row layout. For motor switching, this contactor handles 10 kW at 500 V and 11 kW at 690 V, which covers common three-phase induction motor sizes in those voltage classes. The AC-4 rating of 15.5 A at 400 V is the one to watch if you're doing reversing or inching duty — that's the wear-and-tear rating for frequent plugging or jogging, not just steady-state running. The operating temperature range is -25 to +60 °C, and it's rated for pollution degree 3, so it's suited for industrial environments where conductive dust or condensation might be present. The maximum operating altitude is 2,000 m without derating.
Terminal and wiring details
The main circuit terminals accept solid or stranded conductors: 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or up to 2x (0.75 to 4 mm²). For larger wiring, the same terminals handle 2x (1 to 2.5 mm²), 2x (2.5 to 6 mm²), or a single 10 mm² conductor. In AWG, that's 2x (16 to 12), 2x (14 to 10), or 1x 8 AWG. Short-circuit protection requires a gL/gG fuse: 25 A for Type 2 coordination (no damage to the contactor after a fault) and 63 A for Type 1 coordination (contactor may need replacement but the circuit is cleared). The side-by-side mounting clearance is 6 mm, and the front face is IP20 rated while the terminals themselves are IP00.
Control circuit ratings
The coil operates at 50 Hz, with a voltage tolerance of 0.8 to 1.1 times the rated value. The rated control supply voltage at 50 Hz is 48 V. For auxiliary contact switching, the rated currents vary by voltage: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, 2 A at 60 V, 1 A at 110 V, and 0.3 A at 220 V. The mechanical service life is 10 million operations typical, which is standard for an S0 frame contactor in this class. The reference code per DIN EN 81346-2 is Q, designating it as a switching device in the power circuit.