What this MCB is and where it fits
The Siemens 5SY4603-7 is a 4-pole (3P+N) miniature circuit breaker from the SENTRON series, rated 3 A with a C tripping characteristic. It snaps onto a DIN rail via the quick assembly system and occupies 4 modular width units (72 mm wide). The C curve means it trips at 5–10× rated current — standard for motor and lighting circuits with moderate inrush. Rated breaking capacity is 10 kA per EN 60898 and 35 kA per IEC 60947-2, so it handles fault currents up to those levels without welding or cascading failure upstream. Installation depth is 70 mm, overall depth 76 mm, and it can be mounted in any position. Pollution degree 3 and overvoltage category III suit it for fixed installations in industrial panels where conductive dust or condensation is present. The housing is halogen-free and silicon-free — relevant for environments sensitive to corrosive off-gassing (data centers, clean rooms, food processing). Sealable terminals (top and bottom combined) allow the panel builder to lock the cover after commissioning — common for utility metering or tenant subpanels where tamper evidence is required. IP20 with connected conductors means it's protected against finger contact but not water ingress; keep it inside an enclosure.
Thermal derating — what the 3 A rating actually delivers
The 3 A rating at 35 °C is the baseline. At 45 °C it derates to 2.78 A, at 50 °C to 2.71 A, at 55 °C to 2.62 A, and at 60 °C to 2.54 A. If your panel ambient runs above 35 °C — typical in a packed enclosure with drives or transformers — you need to size the load for the derated figure, not the nameplate 3 A. The humidity envelope is also specified: max 95% RH up to 55 °C, then dropping to 55% at 70 °C and 35% at 75 °C.