The Siemens 3RT1024-1BF44 is a SIRIUS power contactor in the S0 frame size, built for switching motor loads in control panels. It mounts via screw or snap-on onto 35 mm DIN rail per EN 50022, so it drops into any standard panel layout without adapter plates. The 110 VDC coil pulls 5.4 W on close and hold, which matters when sizing a DC supply shared across a row of contactors — that draw is constant, not a spike.
Ratings and what they mean for fit
Rated at 5.5 kW in AC-2 duty at 400 V, this contactor handles wound-rotor motor starts where the current stays moderate through the acceleration. For plugging or inching duty (AC-4), it's rated 12.5 A at 400 V — that's the number to check if your application reverses or jogs the load frequently. The AC-1 resistive rating isn't listed here, so don't assume it for heater banks; stick to the motor-duty figures. The auxiliary contact block carries 2 instantaneous N/O contacts rated 10 A at 24 V, 6 A at 230 V, and 1 A at 110 V DC. That covers feedback to a PLC or holding-circuit interlock, but if you need more than two auxiliary poles, you'll add a side-mount block — the S0 frame accepts them. Operating temperature range is -25 to +60 °C, with a maximum altitude of 2000 m. Pollution degree 3 means it's suited for industrial environments with conductive dust or humidity — no conformal coating required for most panel builds.
Wiring and coordination
Main circuit terminals accept 2x (1 to 2.5 mm²) stranded or 2x (2.5 to 6 mm²), up to 2x 10 mm² max. The auxiliary/control terminals take 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²), max 2x (0.75 to 4 mm²). That's enough for standard panel wire up to about 8 AWG on the mains and 14 AWG on the coil circuit. Screw terminals, not spring-cage — factor in the extra termination time if your shop standard is push-in. Short-circuit coordination: with Type 1 coordination, use a 63 A gL/gG fuse upstream. For Type 2 (no damage to the contactor after a fault), drop to a 25 A gL/gG fuse. That's a real difference in fuse sizing — if your panel spec calls for Type 2, the 25 A limit may force a larger feeder breaker than you'd otherwise run.
Physical fit
Dimensions: 45 mm wide, 85 mm high, 150 mm deep. The 150 mm depth is the dimension that matters most for enclosure depth — it's deeper than a typical 45 mm-wide contactor, so check your gland plate clearance if the panel is shallow. Side-by-side mounting is allowed with 6 mm spacing to adjacent devices, which keeps the rail density high. Protection: IP20 on the front (finger-safe), IP00 at the terminals. That's normal for a panel-mounted contactor — the terminals are live when the cover is off, so standard warning labels apply. No washdown rating; keep it inside the enclosure.