What the ratings mean for fit
The Siemens 5SY7450-6 is a SENTRON miniature circuit breaker — 4-pole, B-curve, rated 50 A at 35 °C. The B characteristic (tripping between 3 and 5 times rated current) is the standard choice for resistive and general-purpose loads where no high inrush exists; it is common in lighting, heating, and distribution subfeeds. The 15 kA breaking capacity per EN 60898 covers most commercial and light industrial panels; the 20 kA rating per IEC 60947-2 gives headroom for higher-fault installations where the prospective short-circuit current exceeds 15 kA. The 400 V AC rating (50/60 Hz) suits three-phase distribution in 400/230 V networks across Europe and other 50/60 Hz regions.
Thermal derating and ambient conditions
The 50 A rating holds at 35 °C. At 45 °C it derates to 47 A, at 50 °C to 45.95 A, at 55 °C to 44.9 A, and at 60 °C to 43.8 A. If the panel ambient runs above 35 °C, use the derated current for the load calculation — the breaker will trip earlier at higher ambient, not later. The operating range spans -40 °C to 75 °C, with humidity limits of 95 % up to 55 °C, 55 % up to 70 °C, and 35 % up to 75 °C. Pollution degree 3 (industrial environment with conductive or dry non-conductive pollution) and overvoltage category III (fixed installation downstream of the main distribution board) are assumed.
Mounting and panel integration
The 5SY7450-6 snaps onto a DIN rail via the quick-assembly system — 4 modular width units (72 mm wide, 90 mm tall, 76 mm deep, 70 mm installation depth). Mounting position is any. The combined top and bottom terminals accept conductors with touch protection (IP20 with connected conductors). The housing is halogen-free and silicon-free, which matters for environments sensitive to outgassing (clean rooms, food processing, certain industrial zones). Sealable — can be locked in the OFF position for lockout/tagout.