SIRIUS S0 Power Contactor — 3RT1024-1AL20-ZW98
It's a current-production part, so you're not hunting for NOS or surplus — this one rolls off the line in Erlangen. The S0 frame size keeps it to a 45 mm wide footprint, which is slim enough to pack three across a standard 600 mm enclosure backplate without forcing a wider gland plate. Rated for AC-4 duty at 12.5 A and 400 V, meaning it's specced for the tough stuff — plugging and inching of squirrel-cage motors where the contactor opens under full load. The AC-2 rating at 5.5 kW and 400 V covers wound-rotor motor starting, and it'll handle 7.5 kW at both 500 V and 690 V in AC-3 service. That's a solid spread for a 45 mm device, and the 25 A gL/gG fuse for Type 2 coordination keeps the short-circuit protection clean.
The 12.5 A AC-4 rating is the one that decides whether this contactor lives or dies in reversing or jogging applications. If your line has a conveyor that reverses direction under load or a press that jogs into position, that 12.5 A figure is your real-world limit, not the higher AC-3 number. The 5.5 kW AC-2 rating at 400 V handles wound-rotor motors where the starting current stays lower but the duty cycle is longer. The screw-type terminals on the main circuit accept 2x (1 to 2.5 mm²) solid or 2x (2.5 to 6 mm²) stranded, with a max of 2x 10 mm². That's enough for the 12.5 A feed without needing a ferrule or bootlace. The auxiliary contacts take 2x (0.5 to 1.5 mm²) solid or 2x (0.75 to 2.5 mm²) stranded, up to 4 mm² max — standard for control wiring in a 24 VDC loop.
Side-by-side mounting is allowed with no derating down to -25 °C, but above that you'll want the 6 mm air gap between units if the ambient climbs toward 60 °C.