SIRIUS Size S0 power contactor — what it handles and where it fits
The Siemens 3RT1025-1AM20 is a SIRIUS Size S0 power contactor rated for motor switching up to 15.5 A in AC-4 duty at 400 V — that's the heavy reversing and plug-stop cycle where most contactors get derated. At 690 V it carries 11 kW, and at 500 V it's good for 10 kW. The 45 mm wide body snaps onto a 35 mm DIN rail per EN 50022, and the screw-type terminals on both main and auxiliary circuits accept up to 4 mm² solid or 6 mm² stranded on the control side, and up to 10 mm² on the power side.
Duty-cycle ratings and coordination
Type 1 coordination requires a 63 A gL/gG fuse upstream; Type 2 coordination needs a 25 A gL/gG fuse.
At 45 mm wide and 85 mm tall, the S0 frame fits two units per standard 100 mm DIN-rail segment. Side-by-side mounting is permitted with no derating — the thermal design accounts for zero spacing. The screw terminals on the main circuit accept 2x (1 to 2.5 mm²) solid or stranded, or a single 10 mm² conductor. Auxiliary and control terminals take 2x (0.5 to 1.5 mm²) solid, or 2x (0.75 to 2.5 mm²) stranded. AWG equivalents are 2x 16-12 for main, 2x 20-16 for aux. Strip length is not listed here, but standard Siemens practice is 8-10 mm for screw terminals in this frame size.