What it is and what it does
The Siemens 3RT1024-1BV40 is a SIRIUS power contactor in the S0 frame size, built for switching motor loads in industrial control panels. It handles 7.5 kW at 400 V in AC-3 duty and the same at 690 V, so it's sized for standard three-phase induction motors up to about 10 hp on a 400 V line. The 24 VDC coil draws 5.4 W both on pickup and hold, which simplifies the DC supply sizing in the panel — no inrush spike to budget for.
Where it fits — panel and mounting
Mounts on a 35 mm DIN rail per DIN EN 50022, either by snapping on or with screws. The S0 footprint is 45 mm wide by 85 mm tall by 101 mm deep, so it takes up a single 45 mm slot on the rail — standard for this class. Side-by-side mounting is allowed with a 6 mm gap to the side, which keeps the row dense without derating. The front face carries an IP20 rating, meaning finger-safe for panel builders; the terminals themselves are IP00, so live parts are exposed once the cover is off.
Key ratings and what they mean for your load
The AC-3 rating at 400 V is 7.5 kW — that's the motor switching number that matters for most conveyor, pump, and fan applications. The AC-4 rating at 400 V is 12.5 A, which covers reversing or inching duty where the contactor makes and breaks under full load. For auxiliary contacts, the 24 V rated value is 10 A, dropping to 2 A at 60 V, 1 A at 110 V, and 0.3 A at 220 V — these are the DC switching limits for the control circuit, so if you're feeding a PLC input, stay within these curves. The operating temperature range is -25 to +60 °C, which covers most indoor panel environments without derating.
Wiring and protection
Main circuit terminals are screw-type, accepting 2x (0.5 to 1.5 mm²) solid, 2x (0.75 to 2.5 mm²) stranded, or up to 4 mm² max. For AWG, that's 2x (16 to 12) solid, 2x (14 to 10) stranded, or 1x 8. For short-circuit protection, Type 2 coordination requires a 25 A gL/gG fuse; Type 1 allows up to 63 A. This matters if the panel spec calls for Type 2 — you need the 25 A fuse limit to avoid damaging the contactor on a fault.