DC miniature circuit breaker for 24 V to 440 V DC control circuits
The Siemens 5SY5214-7CC is a SENTRON 2-pole DC miniature circuit breaker with a C-curve tripping characteristic, rated 0.3 A at 35 °C and 440 V DC. Its 10 kA DC breaking capacity (acc. to IEC 60947-2) means it can safely interrupt a fault current up to that level without welding contacts or cascading failure upstream — critical for DC bus protection in drives, UPS systems, and solar combiner boxes where fault currents are sustained, not zero-crossing like AC. The C-curve (magnetic trip between 5 and 10 times rated current) suits moderate inrush loads like contactor coils, small DC motors, and capacitive loads. At 0.3 A, this is sized for control-circuit protection — think 24 V DC relay panels, PLC power feeds, or signal-conditioner supplies — not main power distribution. The 2-pole design switches both the positive and negative legs in a DC system, which is standard practice for ungrounded or floating DC supplies. Mounts on standard DIN rail via the quick-assembly system in any position. At 36 mm wide (2 modular units) and 76 mm deep, it fits a standard panel enclosure without requiring extra depth for wiring — the 70 mm installation depth leaves clearance for rear-panel busbars or duct. IP20 protection with connected conductors is typical for enclosed distribution boards; not rated for washdown or outdoor exposure.
Thermal derating and environmental limits
Rated current is temperature-dependent: 0.3 A at 35 °C, derating to 0.27 A at 40 °C, 0.25 A at 45 °C, 0.23 A at 50 °C, and 0.21 A at 55 °C. In a sealed panel with no forced ventilation, ambient around the breaker can run 10–15 °C above room temperature — so a 40 °C panel ambient means you're effectively sizing for 0.27 A continuous. The surrounding humidity limits (max 95% at 55 °C, 55% at 70 °C, 35% at 75 °C) reflect condensation risk; not a concern in climate-controlled cabinets but relevant for outdoor or unheated enclosures. Storage and operating temperature range spans -40 °C to 75 °C, with vibration resistance per IEC 60068-2-6 (±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz). Halogen-free and silicon-free construction matters for sensitive environments like semiconductor fab or medical device manufacturing where outgassing can contaminate optics or contacts. Pollution degree 3 (conductive pollution or dry non-conductive pollution that becomes conductive due to condensation) means it's rated for industrial control panels, not clean-room or residential use.