The 3RT1025-1AC20 is a Siemens SIRIUS power contactor, size S0, with a 24 VAC 50/60 Hz coil. It's a panel-mount motor switching device rated for AC-2 and AC-4 duty at 400 V — 7.5 kW in AC-2, 15.5 A in AC-4. That's the rating that governs real motor reversing or plugging service, not the headline thermal current. The 45 mm width per pole saves panel space over older block-style contactors.
Motor power at 400 V AC-2 is 7.5 kW — that's the figure for a standard squirrel-cage start-run duty. The AC-4 rating of 15.5 A covers reversing or inching where the contactor opens under load. Coil is 24 VAC at 50/60 Hz, with a tolerance band of 0.8 to 1.1 times rated voltage at 50 Hz, 0.85 to 1.1 at 60 Hz. That's a standard control voltage for most panels; no special transformer needed. Auxiliary contact ratings: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V. That's enough for pilot duty or PLC input feedback on the same control voltage. Wire range for main contacts: solid 2x (0.5 to 1.5 mm²) up to max 2x (0.75 to 4 mm²), plus AWG equivalents. That covers most motor leads up to 4 mm² stranded.
RoHS compliance date is 01.07.2006, so it meets the EU directive.
The 91 mm depth fits standard enclosures. Fuse coordination: type 2 requires a 25 A gL/gG fuse; type 1 allows 63 A. That's a standard choice — type 2 for semiconductor protection, type 1 for general motor branch circuits.