The Siemens 5SU1353-6KV25 is an FI/LS-protector — a combined residual current device (RCD) and miniature circuit breaker (MCB) in one DIN-rail module. It's a Type A RCD (sensitive to pulsating DC fault currents, as well as sinusoidal AC) paired with a B-curve MCB rated 25 A, in a 1+N-pole package. That 30 mA trip threshold covers personnel protection (shock risk) while the 4.5 kA breaking capacity handles fault currents up to that level without upstream coordination issues.
What the ratings mean for fit
The B-curve trips between 3 and 5 times rated current (75–125 A) for short-circuit protection — standard for resistive and general-purpose loads like lighting, socket outlets, and small control transformers. Type A RCD means it's safe for circuits feeding single-phase electronics (VFDs, switch-mode power supplies) that generate pulsating DC leakage. The 30 mA IΔn is the standard for personal shock protection per IEC 60364. At 70 mm deep (D=70 mm) it fits standard distribution boards with no depth conflict.