The Siemens 3RA1425-8XC21-1AG2 is a SIRIUS wye-delta contactor assembly — a factory-wired group of three contactors (size S0, S0, S0) in a single package that transitions a three-phase motor from wye to delta during startup, cutting inrush current to roughly one-third of direct-on-line levels. Rated 40 A in AC-3 duty at 400 V, it handles motor loads up to 18.5 kW at 400 V, 19 kW at both 500 V and 690 V — the AC-3 figure is the one that governs real motor switching, not the thermal current.
Mounts via screw or snap-on onto 35 mm standard mounting rail per DIN EN 50022 — the same rail as a standard S0 contactor, but the assembly footprint is wider: 158 mm wide, 88 mm tall, 135 mm deep. Zero clearance needed at the sides for side-by-side mounting — you can pack these tight on the rail.
Overload protection and coordination
The current setting range spans 0.8 to 1.1 times the rated value at 50 Hz, and 0.85 to 1.1 at 60 Hz — this is the overload relay adjustment window, not the contactor rating.