The Siemens 3RT1024-1AP04-1AA0 is a SIRIUS power contactor in the size S0 frame, with three normally open main contacts and screw-type terminals for both the main and auxiliary circuits. It's rated for AC-4 switching duty at 12.5 A at 400 V — that's the category for reversing or inching motor starts where the contactor makes and breaks stalled-rotor current, so the contacts take a harder hit than a standard AC-3 run contactor. For AC-2 duty (slip-ring motor starting), it's rated at 5.5 kW at 400 V. Mounting is screw-fixed or snap-on onto a 35 mm DIN rail per EN 50022, and side-by-side mounting is allowed — no derating gap needed between units, which saves rail space in a dense panel. The front face carries an IP20 rating; the terminal area is IP00, so live parts at the connection points are exposed and the panel enclosure provides the final touch protection. Operating temperature range is -25 to +60 °C, and the pollution degree is rated 3 (conductive pollution or dry non-conductive that becomes conductive due to condensation — typical for industrial control panels not in a sealed cleanroom).
Sizing and Coordination
For Type 1 coordination (no damage to the contactor, but contacts may weld after a short circuit), the required upstream fuse is gL/gG 63 A. For Type 2 coordination (contactor remains fully operational after a short, no contact welding), the fuse drops to gL/gG 25 A. That's the spec to hand your panel builder when they're sizing the branch circuit protection. Mechanical life is rated at 10 million operations typical. That's the mechanism itself — electrical life will be lower and depends on the switching category and load current. For a contactor that's seeing frequent inching or reversing (AC-4), expect the electrical endurance to be a fraction of that mechanical figure.
Terminal Capacity and Wiring
Main circuit screw terminals accept 2x (1 to 2.5 mm²), 2x (2.5 to 6 mm²), or max 2x 10 mm² solid/stranded, with AWG equivalents of 2x (16 to 12), 2x (14 to 10), or 1x 8. Auxiliary control circuit terminals take 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or max 2x (0.75 to 4 mm²), with AWG 2x (20 to 16), 2x (18 to 14), or 1x 12. That covers most panel wire gauges you'd run to a contactor coil and aux contacts.