S0 Frame Contactor with AC Coil — What Fits
The Siemens 3RT7025-1AH25 is a size S0 contactor in the SIRIUS family — three main poles, all normally open, with an AC-operated coil. The S0 frame is the mid-range footprint in the SIRIUS line: 55 mm wide, 85.5 mm tall, 91 mm deep, and it snaps onto 35 mm DIN rail per EN 50022 (screw-fix also possible). The AC coil draws 0.72 W on closing and holds at 0.24 W, so the control transformer only needs to cover the inrush peak, not the sustained load. The IP20 rating on the front and terminals means finger-safe but not sealed — install inside an enclosure rated for the environment.
Switching Duty and Coordination
For motor starting (AC-3), the contactor is rated for up to 800 switching cycles per hour. For reversing or inching duty (AC-4), the maximum drops to 250 cycles per hour — the arc energy in AC-4 is higher, so the mechanical life is derated accordingly. Short-circuit protection coordination is specified: for type 2 coordination, use a 25 A gL/gG fuse (NH 3NA); for type 1 coordination, a 63 A fuse of the same class. This matters when the contactor sits downstream of a motor circuit protector — the fuse size determines whether the contactor survives a fault or needs replacement.
The screw terminals accept 2 x (0.5 to 1.5 mm²) solid or stranded, or 2 x (0.75 to 2.5 mm²) with ferrule — strip length is standard for the terminal type.