What it is and what it does
The Siemens 3RT1026-1AL28-0QA2 is a SIRIUS-brand power contactor in the Size S0 frame, designed for switching motor loads in industrial control panels. It mounts via screw or snap-on onto a standard 35 mm DIN rail per EN 50022, which makes it a direct fit for most European-style panel layouts. This contactor carries 11 kW ratings at both 500 V and 690 V under AC-2 duty, and an AC-4 current rating of 15.5 A at 400 V. The AC-2 rating covers wound-rotor motors and slip-ring applications; the AC-4 rating handles inching, plugging, and reversing — the high-stress cycles that generate arcing across the main contacts. Three instantaneous main contacts (3 NO) handle the power circuit, and the contactor is built for 10 million typical mechanical cycles. That mechanical life is what you expect from a S0-frame SIRIUS unit — it's not a light-duty relay, it's meant for daily switching in a production line.
What the key ratings mean for fit
The 11 kW AC-2 rating at 500 V and 690 V tells you this contactor is sized for medium-horsepower induction motors — think 15 HP at 460 V or 20 HP at 575 V, roughly. The AC-4 rating of 15.5 A is the one to watch if your application involves frequent motor reversing or jogging: that's the current the contacts can interrupt under the worst-case arcing conditions. Operating temperature range is -25 to +60 °C, which covers unheated plant floors and hot enclosures near process equipment. Pollution degree 3 means it's rated for conductive pollution environments — typical for industrial panels where dust and humidity are present. Front protection is IP20 (finger-safe), terminal area is IP00 (open). That's standard for panel-mount contactors — the IP20 front means an operator can touch the front of the installed unit without risk, but the wiring area needs to be inside a locked enclosure.
Wiring and coordination
Main circuit terminals are screw-type, accepting 2x (1 to 2.5 mm²) solid/stranded, 2x (2.5 to 6 mm²), or max 2x 10 mm² — also AWG equivalents 2x (16 to 12), 2x (14 to 10), 1x 8. Auxiliary contacts accept 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), max 2x (0.75 to 4 mm²). That's generous for a Size S0; you can parallel two 4 mm² conductors per terminal for high-current feeds. For Type 2 coordination (no-weld after fault), the manufacturer specifies a gL/gG fuse of 35 A. For Type 1 coordination (welding allowed, but no fire risk), the fuse goes up to 100 A gL/gG. If you're designing to IEC 60947-4-1, the 35 A fuse limit is the one that protects downstream equipment after a short circuit. Physical dimensions: 55 mm wide, 85 mm high, 140 mm deep. The 55 mm width is the key panel-space number — it occupies three 18 mm module positions on a DIN rail, which is standard for S0 contactors. Side-by-side mounting is permitted without derating, saving rail space in dense panels.
Lifecycle and sourcing reality
The auxiliary contact ratings span 10 A at 24 V, 6 A at 230 V, down to 0.3 A at 220 V DC. These are the values for the integrated auxiliary contacts — they cover typical PLC-level control signals and pilot duty circuits. The DC ratings are the limiting factor: at 220 V DC the contacts only handle 0.3 A, so verify your DC load before wiring. Maximum operating altitude is 2,000 m without derating. Above that, expect reduced dielectric strength and lower switching capacity — standard for industrial contactors per IEC 60947.