DIN-rail fit and breaking capacity
The Siemens 5SY4318-7 is a 3-pole SENTRON miniature circuit breaker with a C-curve trip characteristic, designed for snap-on mounting to a DIN rail in a distribution board or control panel. Its 54 mm width occupies three modular-width units, and the quick-assembly fastening system lets it clip in without tools. The mounting position is any orientation, which simplifies layout in tight enclosures. The headline rating is a 10 kA breaking capacity at 400 V AC per EN 60898-1, rising to 20 kA per IEC 60947-2 at the same voltage. That means this breaker safely interrupts fault currents up to 20 kA in an industrial panel where the prospective short-circuit current is known to be below that ceiling — a common requirement for sub-distribution boards fed by a larger upstream breaker. For DC circuits, the rated breaking capacity is 15 kA at 60 V (72 V max operating voltage). The C-curve (tripping characteristic class C) means the magnetic trip operates at 5 to 10 times the rated current, making it suitable for circuits with moderate inrush — motor starters, banks of LED drivers, or small transformers — where a B-curve would nuisance-trip on startup but a D-curve would let a hard fault run too long.
Approvals and environmental range
The 5SY4318-7 carries approvals to IEC / EN 60898-1, IEC / EN 60947-2, and UL 1077 / CSA C22.2 No. 235. The UL 1077 listing (5 kA at AC per that standard) is a supplementary protector rating, not a branch-circuit rating — important for panel builders who need to match the breaker to the UL 508A industrial control panel requirements. The pollution degree is 3 (conductive pollution or dry non-conductive pollution that becomes conductive), and the overvoltage category is III, which covers fixed-installation equipment with high availability requirements. Ambient temperature range is -40 °C to 75 °C, with humidity derating: max 95 % RH at 55 °C, tapering to 35 % at 75 °C. The breaker is halogen-free and silicon-free, which matters for environments where outgassing can contaminate sensitive contacts or optics. The IP20 rating (with connected conductors) is standard for enclosed distribution boards — not for wet locations.