What this MCB is and what the ratings mean
The Siemens 5SL4425-0RC is a 25 A, 4-pole miniature circuit breaker (MCB) with a Z characteristic and a 10 kA breaking capacity. The Z characteristic means it trips on short-circuit between 2.5 and 5 times the rated current — tighter than a B curve (3-5×) and faster than a C curve (5-10×) — making it the right choice for protecting semiconductor power supplies, control transformers, and other loads with sensitive electronics that can't tolerate a slower trip. The 10 kA breaking capacity at 400 V AC is the standard rating for this 5SL series, sized for most commercial and light industrial distribution boards where the prospective short-circuit current stays under that threshold.
Where it goes in the panel
Snap-on DIN-rail mounting to a standard 35 mm rail inside a distribution board or sub-panel. The 4-pole format (3 phases + neutral) suits three-phase final sub-circuits where the neutral needs overcurrent protection — common in IEC markets for lighting, socket outlets, and small motor feeds. The Z curve's fast magnetic release keeps downstream semiconductor rectifiers and power supplies from seeing a full fault let-through.