The Siemens 5SL4425-8 is a 4-pole SENTRON miniature circuit breaker with a D tripping characteristic, rated 25 A at 400 V AC. The D-curve means it tolerates high inrush currents — think motor starts, transformer energization, or welding equipment — without nuisance tripping. Breaking capacity is 10 kA per both EN 60898 and IEC 60947-2, so it handles fault currents up to that level on a residential or light commercial infrastructure panel.
What the ratings mean for fit
The 25 A rating holds at 30 °C ambient; at 40 °C it derates to 23.68 A, and at 55 °C to 21.54 A. If your panel runs warm — common in a crowded enclosure — size the load downstream to the derated figure, not the label. The 4-pole design (4P) switches all phases plus neutral, so it's the right choice for a three-phase plus neutral circuit where you want coordinated overcurrent protection on every conductor. Mounting position is unrestricted — install it horizontally, vertically, or upside-down without derating. The IP20 rating (with connected conductors) is standard for enclosed distribution boards; keep it behind a panel door or cover. Sealable terminals (yes) let you lock the cover after commissioning to prevent tamper. Mechanical service life is 10 000 switching cycles typical. That's fine for branch-circuit protection where the breaker operates infrequently; not a daily-switching disconnect. Power loss per pole at rated current is 2.3 W — four poles add up to 9.2 W total heat inside the enclosure, worth factoring into the thermal budget.
Panel integration and compliance
The 5SL4425-8 occupies 4 modular width units (each 18 mm) on a DIN rail, so it needs about 72 mm of rail space. Depth is 76 mm; installation depth 70 mm. That's a standard footprint — fits most residential and light commercial distribution boards without surprises. Halogen-free and silicon-free construction matters for environments where outgassing during a fault could damage electronics or pose a toxicity risk.