MCB for low-current D-curve protection
The Siemens 5SY6614-8 is a 4-pole (3P+N) miniature circuit breaker from the SENTRON 5SY6 series, rated 0.3 A with a D tripping characteristic. The D-curve means it tolerates inrush currents 10–20× rated — designed for loads with high starting surges like small transformers, solenoid valves, or motor starters where a B- or C-curve would nuisance-trip. Breaking capacity is 6 kA per EN 60898 for general distribution and 30 kA per IEC 60947-2 for industrial panel duty, so it handles fault levels common in 400 V AC switchgear without cascading upstream. Rated 400 V AC phase-to-phase, with a maximum DC rating of 72 V for control-circuit applications. The 0.3 A rating is uncommon — most MCBs in this frame start at 1 A or higher — so this part fills the niche for protecting low-current branches where a fuse would normally go, but where resettable overcurrent protection and selectivity are required.
Panel fit and wiring
Mounts on DIN rail via the quick-assembly system, occupying 4 width units (72 mm). Depth is 76 mm, installation depth 70 mm — verify clearance against the enclosure door or backplate. Accepts solid or stranded conductors from 0.75 to 35 mm² at both top and combined terminals, so it can serve as a feeder breaker for larger-gauge wiring or tap down to smaller control circuits. IP20 with connected conductors; touch protection is built in. Mounting position is any, and the supply cord position is also any — no derating required for horizontal or inverted installation. Ambient temperature range -25 to +55 °C operating, -40 to +75 °C storage. Sealable (padlockable) for lockout/tagout procedures. Halogen-free and silicon-free construction suits environments where outgassing must be minimized, such as clean rooms or sealed enclosures.
Standards and approvals
Rated breaking capacity: 6 kA per EN 60898 (household-type MCB standard), 30 kA per IEC 60947-2 (industrial circuit-breaker standard), and 15 kA at DC per IEC 60947-2. Also carries a 5 kA rating at AC per UL 1077 and CSA C22.2 No.235 for North American supplementary protection applications. Overvoltage category III, pollution degree 2 typical for fixed-installation MCBs.