What this MCB is and where it fits
The Siemens 5SJ4210-8HG41 is a 2-pole SENTRON miniature circuit breaker with a D tripping characteristic, designed to protect branch circuits against overloads and short circuits in industrial control panels. It snaps onto a standard DIN rail and occupies 2 modular width units (36 mm). The D curve means it tolerates high inrush currents — the magnetic trip threshold is 10 to 20 times rated current — making it the right choice for motor starter circuits, transformers, or other loads with a heavy starting surge.
Breaking capacity and voltage ratings
Rated breaking capacity is 10 kA per EN 60898 and 15 kA per IEC 60947-2. The higher IEC figure is the one that matters for industrial panel coordination — it tells you this breaker can safely clear a fault up to 15 kA at the rated voltage without welding its contacts or failing catastrophically. AC rated voltage is 400 V; DC rated voltage is 60 V. Insulation voltage (Ui) is rated at 440 V AC.
