What it is and what it does
The Siemens 3RT1026-1KB40-1AA0 is a SIRIUS power contactor in size S0, designed for switching motor loads and resistive loads in industrial control panels. It carries an 11 kW motor rating at 400 V under AC-3 duty (the standard for squirrel-cage motors starting and stopping under load), and the same 11 kW at 400 V under AC-2 duty (slip-ring motors or resistive-inductive loads). The 24 VDC coil draws 4.2 W to close and holds at 4.2 W — a constant-hold design that simplifies the control transformer sizing because there's no inrush-to-hold drop.
Mounting and wiring fit
Mounts on a 35 mm DIN rail per DIN EN 50022, using either the integrated snap-on latch or screws for a more permanent fix. At 45 mm wide, it takes up one standard module slot on the rail. Depth is 101 mm — that's the dimension you need to clear the enclosure door or back panel. Height is 88 mm. Main circuit terminals are screw-type, accepting solid conductors from 2x (0.5 to 1.5 mm²) up to a maximum of 2x (0.75 to 4 mm²), or stranded 2x (1 to 2.5 mm²) up to 2x 10 mm² max. Auxiliary and control circuit terminals are also screw-type. Strip and torque per standard panel practice — these aren't spring-cage, so a screwdriver and a torque driver are part of the install.
Coordination and protection
For Type 1 coordination (no damage to the contactor but may need contact replacement after a fault), the upstream fuse can be gL/gG rated up to 100 A. For Type 2 coordination (no damage at all, the contactor stays functional), the fuse must be limited to 35 A gL/gG. That's a practical difference: if you're designing for minimal downtime after a short circuit, the 35 A fuse limit governs your branch protection choice. The contactor includes an integrated varistor surge suppressor across the coil, so you don't need to add an external RC snubber or diode for DC coil suppression. Pollution degree 3 (conductive pollution) means it's rated for the typical industrial control panel environment without conformal coating.
Thermal and life considerations
Rated for operation from -25 °C to +60 °C ambient, which covers most indoor panel conditions. Mechanical life is 10 million cycles typical — that's the mechanism, not the contacts under load. Electrical life depends on the switching current and duty cycle, but the mechanical figure gives you a floor for maintenance planning in high-cycle applications like conveyor indexing or valve actuation. Side-by-side mounting is allowed without derating (the fastening method permits zero-gap installation), so you can pack multiple contactors on the same DIN rail without worrying about heat buildup between units.