SIRIUS Size S0 Power Contactor — 3RT1025-1BM40-1AA0
The Siemens 3RT1025-1BM40-1AA0 is a SIRIUS power contactor in the Size S0 frame, designed for switching motor loads in control panels. It mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022, occupying 45 mm of panel width. The front face carries an IP20 rating, while the terminals themselves are IP00 — standard for enclosed panel installation. Pollution degree 3 means it tolerates conductive pollution typical of industrial environments, so no conformal coating is required for most cabinet builds. For AC-3 motor starting duty, the contactor is rated at 10 kW at 400 V and 11 kW at 690 V. The AC-4 reversing/inching rating is 15.5 A at 400 V, which governs applications with frequent plugging or jogging. Maximum continuous current in AC-12 resistive load service is 10 A. These are the load-switching limits — the contactor's mechanical life is 10 million operations typical, so it suits high-cycle conveyor or pump stations.
Coil and Control Circuit
The magnet coil draws 5.4 W for both closing and holding — a DC-operated coil with no power reduction after pickup. This simplifies the control transformer sizing: budget 5.4 W per contactor continuously. The coil's switching capacity varies with voltage: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V, and 6 A at 230 V. These are the contact ratings for the control circuit, not the main poles.
Wiring and Short-Circuit Protection
Main circuit terminals accept screw-type connections: solid conductors 2x (0.5–1.5 mm²), 2x (0.75–2.5 mm²), max 2x (0.75–4 mm²). For stranded wire, the range is 2x (1–2.5 mm²), 2x (2.5–6 mm²), max 2x 10 mm². AWG equivalents are 2x (16–12), 2x (14–10), 1x 8. For short-circuit coordination, Type 2 protection requires a gL/gG fuse rated 25 A; Type 1 coordination allows up to 63 A gL/gG. Side-by-side mounting is permitted — the 6 mm side clearance is for heat dissipation, not mandatory spacing.