What this part is and what it does
The Siemens SIRIUS 3RT1026-3XB40-0LA2 is a size S0 power contactor with a 24 V DC coil, designed for switching motor loads in industrial control panels. Its screw-type terminals for the main circuit accept up to 2x 10 mm² conductors, and it mounts via screw or snap-on onto 35 mm DIN rail per EN 50022. For motor duty, the contactor is rated 15 hp at 460/480 V and 20 hp at 575/600 V. In AC-4 service (reversing or inching), it handles 15.5 A at 400 V — the rating that governs frequent plugging or jogging applications.
Key ratings and what they mean for fit
The 24 V DC coil draws a holding current determined by the contactor's magnetic circuit; the pickup voltage threshold is 0.7 times the rated value, meaning the coil must see at least about 16.8 V DC to pull in reliably. Dropout typically occurs below 0.1 to 0.2 times rated, so a saggy 24 V bus won't cause nuisance dropouts unless it collapses below roughly 4 V. Auxiliary contact ratings are given for DC switching: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, and 0.3 A at 220 V. These are the DC-13 inductive load limits — useful for pilot duty on PLC inputs or relay coils in the same panel. The impulse withstand voltage of the main circuit is 6 kV, which covers typical 400 V distribution systems with overvoltage category III. The contactor is rated for operation up to 2,000 m altitude without derating. Clearances required for side-by-side mounting: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 10 mm at the side. The front face carries IP20 protection; the terminals themselves are IP00, so finger-safe shrouds or terminal covers are needed if the panel is live during maintenance.
Panel integration and wiring
The 45 mm width (size S0) fits a standard 45 mm DIN-rail slot. Depth is 100 mm, height 119 mm — verify clearance to the gland plate or enclosure door. Screw terminals accept 2x (0.25...2.5 mm²) solid or stranded, 2x (1...2.5 mm²) and 2x (2.5...6 mm²), with a maximum of 2x 10 mm² per clamp. Mechanical life is 10 million operations typical, which suits high-cycle applications like conveyor diverters or packaging machinery. The contactor supports side-by-side mounting without derating, so multiple units can pack tightly on the rail.