The Siemens 5SY7325-8 is a SENTRON miniature circuit breaker rated 25 A at 35 °C ambient, with a D tripping characteristic that tolerates the high inrush currents typical of motor loads, transformers, and welding equipment — it will not nuisance-trip on a 5× to 10× rated startup surge. The 3-pole design (3P) switches all three phases simultaneously, which is what you need for a three-phase motor branch circuit or a 400 V distribution subfeed. At DC (per IEC 60947-2) it is rated 15 kA, so it also works in DC subdistribution where the voltage is within the device's rating.
Temperature derating — the number that changes your BOM
The 25 A rating holds at 35 °C. Above that, the breaker must be derated: 23.8 A at 40 °C, 23.18 A at 45 °C, 22.55 A at 50 °C, 21.88 A at 55 °C, and 21.2 A at 60 °C. If your panel ambient runs 50 °C, you cannot load this breaker past 22.55 A continuous — a common miss during BOM freeze that leads to thermal tripping on a warm day. The surrounding temperature influence is also specified: max 95% RH up to 55 °C, tapering to 35% at 75 °C.
Panel integration — DIN rail, IP20, quick assembly
The housing is 3 modular width units (54 mm wide, 90 mm tall, 76 mm deep) with an installation depth of 70 mm.
The product designation per IEC 81346-2 and DIN EN 61346-2 is F (protective device).