What this MCB is and what it does
The Siemens 5SY8325-8BB08 is a 3-pole miniature circuit breaker from the SENTRON series, designed for 25 A at 400 V AC with a D tripping characteristic. The D curve means it tolerates high inrush currents — typically 10 to 20 times the rated current — making it a fit for motor, transformer, and lighting ballast circuits where the start-up surge would nuisance-trip a B or C curve breaker. The IEC 60947-2 breaking capacity is 30 kA at 400 V AC, so it clears a fault up to that level without welding contacts or cascading upstream. The UL 1077 / CSA C22.2 No. 235 rating is 5 kA, which covers most North American panelboard applications.
Panel fit and mounting
Snaps onto a DIN rail via the quick assembly system — no tools needed for the rail, just a screwdriver for the terminals. Occupies 3 width units (54 mm) and requires 70 mm installation depth behind the panel. The housing is IP20 with conductors connected, which is standard for enclosed distribution boards. Terminal positions are top and bottom combined, so line and load can land on either end. Mounting position is any, and the unit is sealable for tamper-proofing after commissioning.
Environmental and compliance notes
Halogen-free and silicon-free construction, rated for ambient temperatures from -40 °C to 75 °C. Humidity tolerance: max 95% at 55 °C, derating to 35% at 75 °C. Overvoltage category III, pollution degree 3 — suitable for industrial fixed installations where the breaker sees transient overvoltages from the supply. Mechanical service life is 10 000 switching cycles typical.