SIRIUS S0 power contactor, 24 VDC coil, varistor suppression
The Siemens SIRIUS 3RT1026-3KB44-1LA0 is a size S0 power contactor rated for motor switching at 11 kW in AC-3 duty at 400 V and also 11 kW at 690 V, making it a single part for 400 V and 690 V motor circuits up to that load. The 24 VDC magnet coil draws 23 W on pickup and holds at 7 W, with an operating range of 0.7 to 1.25 times rated voltage — so it picks up reliably at 16.8 V and won't drop out until below that threshold. Built-in varistor surge suppression across the coil means you don't need an external RC snubber for inductive kickback; just watch polarity on the DC coil wiring. Snap it onto 35 mm DIN rail per EN 50022 or screw-mount — the S0 frame is compact at 70 mm wide, 88 mm tall, and 153 mm deep, so it fits standard panel layouts without crowding adjacent devices. Side-by-side mounting is allowed with no derating, but if you need full rated current in a hot cabinet, leave 6 mm side clearance for airflow.
Motor duty and coordination
This contactor is rated for AC-3 (cage motor starting) at 11 kW / 400 V and the same 11 kW at 690 V — so it handles standard 400 V motors and 690 V motors of the same power without upsizing. For AC-4 reversing or plugging duty, the rating drops to 15.5 A at 400 V, which is the figure to use for frequent inching or reversing applications. AC-2 (slip-ring motor) rating is also 11 kW at 400 V. For short-circuit coordination, Type 1 requires a 100 A gL/gG fuse; Type 2 (limited damage to the contactor) needs a 35 A gL/gG fuse. The main circuit terminals are screw-type accepting 2x (0.25 to 2.5 mm²) solid or 2x (1 to 6 mm²) stranded, with a maximum of 2x 10 mm² or 1x 8 AWG — enough for the motor leads on this size.
Auxiliary contacts and environmental ratings
Two instantaneous auxiliary contacts are built in, rated for 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V — covering typical PLC and relay interface voltages. The front face carries IP20 protection (finger-safe), while the terminal area is IP00 (open). Pollution degree 3 means it's suited for industrial environments with conductive pollution, and the operating temperature range of -40 to +70 °C covers cold storage areas and hot cabinet interiors. Maximum operating altitude is 2 000 m without derating. Mechanical endurance is rated at 10 million operations typical, which for a contactor on a conveyor or pump running once per minute gives over 19 years of service life before mechanical wear — electrical life will be shorter and depends on the switching load and frequency.