What it is and where it lands
The Siemens 5SY6318-7 is a SENTRON 3-pole miniature circuit breaker with a C tripping characteristic and a 15 A rated current at 35 °C. It snaps onto a DIN rail via the quick assembly system and occupies 3 modular width units (54 mm). The C-curve means it trips between 5 and 10 times rated current — standard for motor and general distribution loads where moderate inrush is expected.
Breaking capacity — what the dual rating means
This breaker carries two breaking ratings: 6 kA per EN 60898-1 and 15 kA per IEC 60947-2 / UL 1077. The EN 60898 figure governs residential and light commercial distribution boards; the higher IEC 60947-2 rating applies when the breaker is used in an industrial panel as a branch-circuit protective device per UL 1077. The 15 kA rating gives headroom for higher fault-current locations without cascading upstream.
Thermal derating — the real current at panel ambient
The 15 A rating is at 35 °C. At 40 °C the continuous current drops to 14.28 A; at 45 °C it's 13.9 A; at 50 °C it's 13.53 A; at 55 °C it's 13.12 A. If your panel ambient runs at 50 °C, size the load at 13.5 A — not the 15 A nameplate. The breaker also handles humidity up to 95% at 55 °C, derating to 35% at 75 °C.
Physical fit and environment
Depth is 76 mm, installation depth 70 mm, width 54 mm (3 MW), height 90 mm. Rated IP20 with connected conductors — suitable for enclosed distribution boards and control panels, not for washdown or outdoor exposure. Pollution degree 3 (conductive or dry non-conductive pollution), overvoltage category III. Mount in any position. Sealable for tamper-proof applications. Halogen-free and silicon-free construction.