What it is and where it fits
The Siemens SIRIUS 3RT2025-1AL20-1AA0 is an S0-frame power contactor with a 24 VDC magnet coil and screw-type terminals. It snaps onto a 35 mm DIN rail per DIN EN 60715 and sits in a 45 mm wide slot — standard for control-panel layouts where every millimeter of rail space is accounted for. Rated for up to 1 000 switching cycles per hour under AC-1, AC-2, and AC-3 duty, and 300 cycles per hour under AC-4, it handles frequent inching or jogging without derating the mechanical life of 10 million operations typical for this contactor family.
What the ratings mean for your panel
The S0 frame is the workhorse size for motor loads up to around 7.5 kW at 400 V AC-3 (the exact motor rating depends on the coil voltage and auxiliary contact configuration). The 45 mm width and 97 mm depth let it fit alongside other SIRIUS devices in a standard distribution board without crowding the wiring ducts. Clearance distances are specified: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm at the side. That matters when you are packing multiple contactors side-by-side — you can butt them at 6 mm spacing without losing arc-quenching performance. The screw-type coil terminals accept solid or stranded wire from 1 to 10 mm², and the main contact terminals accept two conductors per clamp (2x 0.5...1.5 mm² or 2x 0.75...2.5 mm²). That is enough for paralleling a motor lead and a feedback wire without a separate terminal block.