Integrator note — B-curve MCB for 400 V AC branch circuits
It breaks 10 kA per EN 60898-1 and 20 kA per IEC 60947-2, with a DC breaking capacity of 15 kA per IEC 60947-2. Occupies a single 18 mm modular width on DIN rail, mounts in any position, and accepts supply from either end. The quick-assembly system clips onto the rail without tools.
Sourcing & lifecycle — active, no phase-out signal
Lifecycle status is current. The 5SY4125-6 remains in Siemens' active SENTRON catalog for new installations and replacement spares.
Compliance & approvals — three-standard rated
Rated under three standards: EN 60898-1 (10 kA), IEC 60947-2 (20 kA AC, 15 kA DC), and UL 1077 / CSA C22.2 No.235 (5 kA). The UL 1077 listing means it is recognized as a supplementary protector in North American panels — not a branch-circuit rated breaker per UL 489, but accepted for internal equipment protection. Halogen-free and silicon-free construction reduces outgassing in sealed enclosures. Sealable for lockout/tagout compliance.
Panel fit — 18 mm width, 70 mm installation depth
Width of 18 mm (one modular unit) and installation depth of 70 mm from the DIN rail face. Overall depth is 76 mm including the front toggle. IP20 with connected conductors means the terminals are finger-safe once wired.