The Siemens 3RA2125-1DD23-0AP6 is a SIRIUS non-fused motor starter (product designation: non-fused motor starter 3RA2) built as a direct starter, meaning it combines a contactor and overload relay in one assembly without requiring upstream fuses for short-circuit protection — the integrated circuit-breaker handles that. It is a Size S0 load feeder, which governs the physical envelope and the maximum motor current it can switch; the supplied contactor is a 3RT2023-1AP60 and the supplied link module is a 3RA2921-1AA00. This starter is designed to snap onto 60 mm busbar systems, so it integrates directly into a standard panel busbar layout without extra brackets — common in motor control centers where space per feeder is tight. It is rated for AC-3 duty up to 690 V, which covers the majority of three-phase motor applications up to that line voltage, and carries a Class 10 trip characteristic — meaning the overload relay will trip within 10 seconds at 7.2× the set current, fast enough to protect standard induction motors during a locked-rotor event.
At 400 V the starter is rated for 1 100 W (roughly 1.5 hp), and at 480 V it draws 2.8 A — so for a 480 V supply this unit handles motors up to about 1.5 hp (the 460/480 V rating is 1.5 hp). The overload release is thermal (bimetallic), which means it tracks the motor's heating curve naturally and does not require a separate power supply for the trip function — it responds to the current heating the bimetal strip.
Mounting and environment — built for the panel, not the office
Mounting position is vertical only, which is standard for contactor-based starters to ensure proper arc extinction and thermal overload calibration. Operating temperature range is -20 to +60 °C, storage from -50 to +80 °C, and transport from -55 to +80 °C — so it survives the ride in an unheated truck and runs in a hot panel without complaint. Clearances required around the unit: 30 mm upwards, 10 mm forwards, 10 mm downwards, 9 mm at the side, and 0 mm backwards — the back can sit flush against the mounting surface.