The Siemens 5SU1654-6KV25 is an FI/LS-protector — a combined residual-current device and miniature circuit breaker in one 1+N-pole unit, B characteristic, rated 25 A. The residual-current section is Type A, 300 mA sensitivity, with a 10 kA short-circuit capacity. The D=70 mm width matches the standard Siemens modular DIN-rail footprint, so it slots into a distribution board alongside other 70 mm-wide devices without extra adapters.
What the ratings mean for fit
The B characteristic (3–5× In magnetic trip) means the unit is sized for resistive and light inductive loads — lighting circuits, small heaters, general socket outlets — not for motor starting or transformer inrush, where a C or D curve would be the correct choice. The 300 mA residual sensitivity (Type A) detects sinusoidal AC fault currents plus pulsating DC fault currents up to 6 mA smooth DC, which covers most modern electronic loads (SMPS, LED drivers, VSDs) that a plain AC-type RCD would miss. The 10 kA breaking capacity at 230/400 V is the standard domestic and light commercial fault level; if the prospective short-circuit current at the point of installation exceeds 10 kA, the device needs a back-up fuse or a higher-rated upstream breaker.