The 3RW4427-1BC36: This SIRIUS soft starter is rated 161 A at 40 °C ambient — that is the full-load current it can start continuously without derating. Push the ambient to 50 °C and the continuous rating drops to 142 A; at 60 °C it falls to 125 A. The 40 °C baseline is the one to size against for a standard 40 °C panel environment. The integrated bypass contact system means the thyristors are shorted out once the motor reaches full speed, eliminating SCR conduction losses in steady-state. That keeps the enclosure cooler and lets the soft starter sit closer to other heat-generating gear on the DIN rail. Minimum load is 8 % of the rated current — so this unit handles lightly loaded conveyors or pumps without dropping out of regulation. Below that threshold the SCR firing angle may not maintain a clean output.
Mounting, clearances, and wiring — panel-fit constraints
The unit measures 170 mm wide by 192 mm high by 270 mm deep, fastened with screw fixing. It needs 100 mm clearance above, 75 mm below, and only 5 mm at the sides — tight side-by-side packing is fine, but the vertical airflow path must stay open. Mounting position is flexible: vertical surface with ±90° rotation and ±22.5° tilt forward/back. That covers most panel layouts without special brackets. Main circuit terminals are box lugs accepting 2x (4 … 50 mm²) stranded or 2x (10 … 1/0 AWG) using both clamping points. The back and front clamping points each take 10 … 2/0 AWG. Maximum motor cable length is 500 m — adequate for most installations but worth checking on long runs where capacitive charging current might nuisance-trip the overload protection.
Protection and control features
Built-in motor overload protection and intrinsic device protection are standard — no separate overload relay needed. Adjustable current limitation lets you cap inrush to a multiple of the motor FLA, useful on weak supplies or generators. The unit supports inside-delta wiring (six-wire connection), which reduces the current through each SCR leg by 58 % compared to standard three-wire. That extends the current range of the same hardware into larger motors without stepping up the frame size. Pollution degree 3 per IEC 60947-4-2 means it is rated for industrial environments with conductive dust or occasional condensation — no need for a sealed enclosure in a typical panel. Operating frequency covers 50 … 60 Hz — same unit for either grid standard.
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