The Siemens SIRIUS 3RT1026-3KF40-1AA0 is a size S0 power contactor rated 11 kW in AC-2 duty at 400 V — that is the motor-switching curve for slip-ring or wound-rotor motors, where the contactor makes and breaks under full load. The AC-4 reversing rating is 15.5 A at 400 V, which governs plugging or inching applications where the contacts open under stalled-rotor current. The magnet coil is wound for 110 V AC and includes a built-in varistor surge suppressor, so no external RC snubber is needed across the coil terminals.
Panel fit and wiring constraints
The S0 footprint is 45 mm wide by 88 mm tall by 101 mm deep — a standard width that leaves room for a three-phase busbar system alongside. Main-circuit terminals are screw-type, accepting 2x (0.25 to 2.5 mm²) solid or 2x (1 to 2.5 mm²) stranded, with a maximum of 2x 10 mm² per terminal.