What this MCB is and where it fits
The Siemens 5SJ4104-8HG42 is a SENTRON miniature circuit breaker with a D tripping characteristic, designed for one-pole protection in 50 Hz systems. It snaps onto a standard mounting rail and occupies one modular width unit (18 mm), making it a direct fit for any DIN-rail panel that expects a single-pole MCB. The D-curve means it tolerates high inrush currents — typical for motor starters, transformers, or lighting ballasts — without nuisance tripping on startup.
Key ratings and what they mean for your panel
Rated breaking capacity is 10 kA per EN 60898 and 15 kA per IEC 60947-2 at 400 V AC. The higher IEC figure applies when the MCB is used as a distribution breaker in industrial panels; the EN figure covers residential or commercial final circuits. Either way, it clears faults up to those levels without welding contacts or cascading upstream. Insulation voltage (Ui) is 440 V AC, so it's comfortable on 400 V line-to-line systems. DC rating maxes at 60 V — useful for control-circuit protection but not for high-voltage DC bus work. Pollution degree 3 and overvoltage category 3 mean the breaker is rated for industrial environments where conductive dust or condensation may occur — typical for factory-floor panels, not just clean switchboards. IP20 with connected conductors (IP40 in the handle area) is standard for enclosed distribution boards; the sealable feature (padlockable handle) allows lockout/tagout without an external accessory.
Mounting and wiring details
Depth is 70 mm, height 121 mm, width 18 mm. Halogen-free and silicon-free construction.