What it is and what it does
The Siemens SENTRON 5SY4325-8FA is a 3-pole miniature circuit breaker (MCB) with a D tripping characteristic, rated 25 A at 35 °C and breaking 10 kA per EN 60898 at 440 V AC. The D curve means it tolerates high inrush currents — typical for motor, transformer, or welding loads — without nuisance tripping, while still clearing a fault fast enough to protect the downstream cable. It occupies 3 modular width units (54 mm) on a DIN rail and mounts in any position, which simplifies panel layout when space is tight.
Ratings and what they mean for fit
The 25 A rating holds at 35 °C ambient; at 40 °C it derates to 23.8 A, and at 55 °C to 21.88 A. If your panel runs hot — say, inside a crowded enclosure near other heat sources — you need to account for that derating or step up to a higher-rated frame. The 10 kA breaking capacity per EN 60898 is the standard for residential and light commercial distribution boards; for industrial panels with higher available fault current, you'd want to verify the SCCR at the panel level. The 440 V AC rating covers both single-phase and multi-phase operation, so it works across 230/400 V systems common in European and Asian installations.
Integration notes
Mounts on a DIN rail via the quick assembly system — no tools needed for snapping on or off. The combined terminal at top and bottom accepts the same conductor size, so wiring order doesn't matter. Depth is 76 mm (installation depth 70 mm), which fits standard 80 mm deep enclosures. IP20 with connected conductors means it's protected against finger contact but not washdown; keep it inside a sealed panel if the environment is wet or dusty. Pollution degree 3 and overvoltage category III suit it for fixed installations in industrial or commercial buildings.