What it is and what the ratings mean
The Siemens 5SY6504-8CC is a SENTRON miniature circuit breaker with a D tripping characteristic, rated 4 A at 35 °C ambient. The D curve means it tolerates high inrush currents — typically motor and transformer starts — without nuisance tripping, while still clearing a 6 kA fault per EN 60898. That 6 kA is the short-circuit breaking capacity at 250 V AC single-phase; it safely interrupts faults up to that level without welding the contacts or cascading upstream. This is a 2-pole breaker in a 1P+N design — it switches both the line and the neutral conductor, which is required in some regional codes for final subcircuits. The neutral pole is switched, not just solid-linked, so it isolates both sides when opened. It occupies 2 modular width units (36 mm) on a DIN rail, with a depth of 76 mm and an installation depth of 70 mm. Rated operating voltage is 250 V AC single-phase at 50/60 Hz. The breaker is also rated for DC operation up to 72 V, though the DC breaking capacity is not listed here — verify for DC circuits. Pollution degree 3 and overvoltage category III mean it's suited for industrial panels where conductive dust or condensation may be present.
Derating and temperature influence
The 4 A rating holds at 35 °C. Above that, the breaker must be derated: 3.76 A at 40 °C, 3.64 A at 45 °C, 3.5 A at 50 °C, and 3.37 A at 55 °C. If the panel ambient runs hot — say inside a sealed enclosure near a drive — size the circuit for the derated value, not the 35 °C number. The surrounding temperature influence also caps relative humidity: 95% up to 55 °C, dropping to 55% at 70 °C and 35% at 75 °C. Operating temperature range is -40 °C to 75 °C, so it handles cold starts in unheated warehouses or outdoor cabinets. Mounting position is any — no derating needed for horizontal or inverted installation.
Panel integration and compliance
Snaps onto a DIN rail via the quick assembly system — no tools needed for mounting. Combined terminals top and bottom accept the same conductor range; the sealable cover option (yes, sealable) lets you lock the setting against tamper after commissioning. IP20 with connected conductors means it's protected against finger contact but not water ingress — standard for enclosed distribution boards. Halogen-free and silicon-free construction matters for sensitive environments like clean rooms or semiconductor fabs where outgassing can contaminate optics or contacts. The breaker is designated for mechanical engineering and industry per its suitability listing.