Rated current and trip curve — what drives the fit
The Siemens 5SY5450-7 is a 4-pole SENTRON miniature circuit breaker rated 50 A at 35 °C with a C-curve trip characteristic. That C-curve means the magnetic trip fires between 5 and 10 times rated current — 250 to 500 A — which suits motor-starting inrush and moderate transformer loads without nuisance tripping on the branch circuit. At 40 °C the rating derates to 48 A; at 50 °C it drops to 45.95 A, and at 60 °C to 43.8 A. If your panel ambient runs above 35 °C, size the upstream protection for the derated value, not the nominal 50 A.
Breaking capacity and voltage — AC and DC sides
Breaking capacity is 10 kA per EN 60898 on the AC side, and 10 kA per EN 60898-2 on the DC side at 880 V. That 880 V DC rating is the standout — most 4-pole MCBs in this frame top out at 440 V DC. The 5SY5450-7 handles both poles in series for the DC path, so it's a candidate for 880 V battery banks or DC bus protection where you'd otherwise need two breakers in series. The voltage type is AC/DC universal current; on DC supply, observe polarity as marked.
Physical fit and panel integration
The breaker occupies 4 modular width units (72 mm wide) on a DIN rail. Depth is 76 mm; installation depth behind the panel is 70 mm. Mounting position is any orientation, which helps in tight enclosures. The quick assembly system snaps onto the rail without tools. Combined terminals top and bottom accept the same conductor range — no special feed-through lug needed. IP20 with connected conductors, pollution degree 2, overvoltage category II. Sealable, halogen-free, silicon-free.