What it is and where it fits
The Siemens SIRIUS 3RT1025-1AL20-ZW98 is a size S0 power contactor with a 230 V AC 50/60 Hz coil, screw-type terminals for the main circuit, and a 45 mm wide body that snaps onto a 35 mm DIN rail per EN 50022. Rated for motor loads: 7.5 kW at 400 V in AC-2 duty, and 15.5 A at 400 V in AC-4 (reversing or inching). The coil pulls 10 A at 24 V and 6 A at 230 V, so the control transformer needs to be sized for that inrush. Mechanical life is 10 million operations typical, and the contactor is rated for side-by-side mounting with 6 mm clearance at the side, which keeps the panel width tight.
Mounting and wiring constraints
Mounts via screw or snap-on onto 35 mm DIN rail. The front is IP20; the terminal area is IP00, so the panel builder needs to account for that when laying out gland plates and busbars. Main circuit screw terminals accept 2x (1... 2.5 mm²) stranded or 2x (2.5... 6 mm²) solid, max 2x 10 mm². Control circuit terminals take 2x (0.5... 1.5 mm²) solid, 2x (0.75... 2.5 mm²) stranded, max 2x (0.75... 4 mm²). AWG equivalents: main 2x (16... 12) or 2x (14... 10), control 2x (20... 16) or 2x (18... 14). Pollution degree 3 rating means it's suitable for industrial environments with conductive pollution; no additional conformal coating needed for most panel conditions.
Coordination and protection
For Type 2 coordination (no damage to the contactor on short circuit), use a gL/gG fuse rated 25 A. For Type 1 coordination (contactor may need replacement after fault), the fuse can be 63 A. Rated for operation up to 2000 m altitude without derating; above that, the dielectric strength and thermal dissipation need to be checked against the application.