What it is and what it does
The Siemens 3RT1026-1CD25 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads in industrial control panels. It mounts via screw and snap-on onto a 35 mm DIN rail per DIN EN 50022, so it drops into standard panel layouts without extra bracketry. Rated for AC-4 duty at 15.5 A at 400 V, this contactor handles the severe switching conditions of plugging, inching, and reversing motor starts where the contacts make and break full locked-rotor current. That AC-4 figure is the one that governs real motor-reversing or jogging applications — not the thermal continuous current. Operating temperature range is -25 to +60 °C, with a maximum altitude of 2 000 m, so it suits unconditioned enclosures in most plant environments.
Panel integration and wiring
Screw-type terminals on the main circuit accept 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or up to 2x (0.75 to 4 mm²) solid/stranded, plus AWG equivalents. The auxiliary contact block is a single instantaneous contact (1 NO/NC configurable). Side-by-side mounting is allowed with a 6 mm spacing to adjacent devices, keeping DIN-rail density practical. Front face is IP20; the terminal area is IP00, so the contactor needs to live inside a panel or enclosure with a higher overall ingress rating. Pollution degree 3 means it tolerates conductive pollution typical of industrial control rooms — no special coating required.