The Siemens SIRIUS 3RA2125-4DD27-0AP6 is a non-fused motor starter in size S0, configured as a direct starter. It ships with a 3RT2027-1AP60 contactor and a 3RA2921-1AA00 link module, plus a thermal bimetallic overload relay set to Class 10 trip curve. Rated for 22.2 A at 480 V and 11 kW at 400 V, it handles motors up to 15 hp at 460/480 V or 20 hp at 575/600 V. The coil accepts 176–242 V at 50 Hz and 192–264 V at 60 Hz. Mounting is vertical, snapping onto 60 mm busbar systems — no DIN rail adapter needed. The unit is 45 mm wide, 155 mm deep, and 260 mm tall, with 30 mm clearance upward, 10 mm forward and downward, and 9 mm at the sides. Pollution degree 3 rated, it operates from -20 to +60 °C and stores from -50 to +80 °C. The thermal bimetallic design tracks motor heating closely, resetting automatically after cooldown. Wire range for main contacts is 1–10 mm² stranded, or 2× (2.5–6 mm²).
The SIRIUS family is a broadly stocked, fast-moving line across MRO inventories. If you are kitting a panel that was originally specified with a 3RV2023-4DA10 or similar S0 circuit-breaker-based starter, the 3RA2125-4DD27-0AP6 is a non-fused alternative — same S0 footprint, same busbar snap-on, but with the overload and contactor integrated as a single order code rather than a separate breaker. No rewiring of the load feeder is needed if the panel was laid out for S0 components.
Wire the main circuit with 1–10 mm² stranded conductors. For dual-feed applications, two conductors of 2.5–6 mm² each are permitted. The supplied link module bridges the contactor and overload — no extra bus bars needed. Coil wiring is polarity-sensitive for DC versions; this AC coil has no polarity requirement.