What this MCB is and what the ratings mean
The Siemens 5SY7520-7CC is a SENTRON miniature circuit breaker (MCB) with a 1P+N pole design — it switches the line and the neutral, which matters when you need full isolation on a single-phase circuit and the neutral conductor must be opened with the phase. Rated 20 A at 35 °C with a C tripping characteristic (magnetic trip between 5 and 10 times In), it is sized for general-purpose branch-circuit protection where moderate inrush from motor starters or capacitor banks is expected. The 25 kA breaking capacity per IEC 60947-2 at 250 V AC means it can safely interrupt a fault current up to that level without welding its contacts or cascading damage upstream — that is the figure that governs coordination with the upstream protective device, not the thermal rating alone.
Thermal derating — the real-world current capacity
The 20 A rating holds at 35 °C ambient. Above that, the thermal-magnetic element must be derated: 18.54 A at 40 °C, 17.76 A at 45 °C, 16.94 A at 50 °C, and 16.08 A at 55 °C. If the panel ambient runs at 50 °C, this breaker is effectively a 17 A device. The datasheet also specifies the surrounding humidity envelope: max 95% RH up to 55 °C, tapering to 35% at 75 °C. For a sealed enclosure with internal heat rise, factor the derating into the load calculation before committing the BOM line.
DIN-rail fit and panel integration
Occupies 2 modular width units (36 mm) on a DIN rail, with a depth of 76 mm and an installation depth of 70 mm. The quick-assembly fastening system snaps onto the rail without tools. Mounting position is any orientation, which simplifies layout in crowded enclosures. Combined terminals at both top and bottom accept the incoming and outgoing conductors — no need for a separate neutral bar if the circuit requires neutral switching. Pollution degree 3 and overvoltage category III suit industrial control panels where conductive dust or condensation is present.
Compliance and material declarations
Halogen-free and silicon-free construction, per the spec. Sealable — the breaker accepts a lockout tagout hasp for LOTO procedures. The product designation per EN 61346-2 and IEC 81346-2 is function code F (protective device). Suitability is marked for mechanical engineering and industry applications. The IP20 protection class applies with connected conductors, meaning the terminals are finger-safe once wired.