What this SIRIUS S0 contactor is and what it does
The Siemens 3RT1026-3KF44-1LA0 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads in industrial control panels. It mounts via screw or snap-on onto a 35 mm DIN rail per EN 50022, fitting into standard enclosure layouts. The 110 V DC coil with integrated varistor handles the suppression internally, so you don't need to add a separate RC snubber across the coil terminals.
Key ratings and what they mean for your motor circuit
For motor starting duty (AC-2 at 400 V), this contactor is rated at 11 kW — that covers a standard 15 hp induction motor on a 400 V three-phase line. For reversing or plugging duty (AC-4 at 400 V), the rating drops to 15.5 A, reflecting the higher electrical wear from breaking locked-rotor currents. The mechanical endurance is typical 10 million cycles, so it's built for high-throughput conveyor or pump cycling applications. The contactor carries pollution degree 3, meaning it's rated for the conductive dust and humidity found in most industrial environments without conformal coating. The front face is IP20 (finger-safe), while the terminals are IP00 — they need to be inside a cabinet or shrouded for touch protection. Operating temperature range spans -40 to +70 °C, so it's suitable for unheated plant floors or outdoor cabinet installations as long as the enclosure keeps condensation off the terminals.
Short-circuit coordination and wiring
For Type 2 coordination (no damage to the contactor after a short-circuit), Siemens specifies a 35 A gL/gG fuse upstream. For Type 1 coordination (contactor may need replacement but the rest of the panel survives), a 100 A gL/gG fuse is allowed. The main terminals are screw-type, accepting 2x (1 to 2.5 mm²) or 2x (2.5 to 6 mm²) or up to 2x 10 mm² stranded copper.
Panel integration notes
The S0 frame occupies 70 mm width, 88 mm height, and 153 mm depth — check your DIN rail clearance, especially if the contactor is mounted near the gland plate. Side-by-side mounting is allowed (zero spacing), so you can pack multiple units on the same rail without derating. The auxiliary contact block (2 instantaneous contacts) is built in; no separate add-on needed for basic signaling.