What this contactor is and where it fits
The Siemens 3RT1024-3KB40 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads in control panels. Its 24 VDC coil draws 4.2 W during both closing and holding, so the control transformer or DC supply must be sized for that steady-state draw — no inrush spike to worry about on DC. The varistor surge suppressor is built in, meaning no external snubber needed for coil suppression. Mounting is screw or snap-on onto 35 mm DIN rail per EN 50022, and side-by-side mounting is allowed with 6 mm spacing at the side. The IP20 front enclosure keeps fingers out; the terminal area is IP00, so the panel builder must account for that in the gland plate layout — no arc flash protection at the terminals themselves.
Key ratings and what they mean for your motor load
The AC-3 motor-switching rating at 400 V is not directly stated, but the AC-2 rating at 400 V is 5.5 kW and the AC-4 rating at 400 V is 12.5 A. For a typical three-phase induction motor, the AC-3 rating would be higher than AC-2 — expect this contactor to handle a 5.5 kW motor in standard starting duty. The 7.5 kW rating at both 500 V and 690 V confirms it can handle higher-voltage motors in those regions. For resistive or general-purpose loads (AC-12), the maximum operating current is 10 A. The auxiliary contact ratings span from 10 A at 24 V down to 0.3 A at 220 V and 3 A at 400 V — useful for pilot-duty circuits. Mechanical life is rated at 10 million operations typical, so it holds up in high-cycle applications like conveyor zone control.
Panel integration and wiring
Dimensions are 45 mm wide, 88 mm high, and 100 mm deep — the S0 frame fits standard 45 mm DIN-rail spacing. Main circuit terminals accept screw-type connections: 2x (0.25 to 2.5 mm²) solid, 2x (1 to 2.5 mm²) stranded, up to 2x 10 mm² max. AWG equivalents are 2x (16 to 12) solid, 2x (14 to 10) stranded, or 1x 8. For type 2 coordination, use a gL/gG fuse rated 25 A; for type 1, 63 A. Operating temperature range is -25 to +60 °C. Maximum operating altitude is 2 000 m. Pollution degree 3.