What it is and where it fits
The Siemens 3RT1026-3BD40 is a SIRIUS power contactor in frame size S0, rated for motor switching at 11 kW under AC-2 duty at 400 V and 15.5 A under AC-4 inching duty at 400 V. It mounts on a 35 mm DIN rail per EN 50022 with screw and snap-on fastening, occupying a 45 mm width — a standard slot in any S0 panel layout.
What the ratings mean for the buyer
The AC-2 11 kW at 400 V rating covers slip-ring motor starting where the contactor opens under load at reduced current — typical for crane or hoist applications. The AC-4 15.5 A rating handles plugging and inching duty where the contactor makes and breaks stalled-rotor current; if your application cycles the motor direction or inching frequently, this is the figure that governs contact life, not the AC-2 number. Type 2 coordination is met with a 35 A gL/gG fuse upstream, meaning the contactor remains usable after a short-circuit fault — no welded contacts, minimal downtime. For Type 1 coordination (replace after fault), a 100 A gL/gG fuse suffices. Mechanical endurance is rated at 10 million cycles typical; the DC coil draws 5.4 W both on closing and holding, so no inrush surge to stress the control transformer.
Termination and wiring
Main power circuit uses screw-type terminals accepting 2x (0.25...2.5 mm²) solid or 2x (1...2.5 mm²) stranded, up to 2x 10 mm² max. Auxiliary and control circuits use spring-loaded terminals (2x 0.25...2.5 mm² solid, 2x 24...14 AWG) — no screw tightening needed on the aux side, which speeds panel wiring.