Siemens 5SU1353-0KV20 is a combined residual-current device and miniature circuit breaker (RCBO), often called an FI/LS protector in European panel practice. It integrates Type AC residual current detection at 30 mA with overcurrent protection on a B-curve 20 A, single-pole plus neutral, rated to 4.5 kA breaking capacity. The 'WS' designation indicates a neutral-switching variant — the neutral pole opens with the line pole, which matters for circuits where the neutral must be positively disconnected during fault clearing or isolation.
The 70 mm depth (D=70MM) fits standard Siemens distribution board cutouts and most European modular enclosures. Type AC detection covers sinusoidal AC residual currents — the common fault type in domestic and light commercial circuits feeding resistive, inductive, or electronic loads without DC components. For circuits with variable-speed drives, UPS, or LED drivers that generate pulsed or DC fault currents, a Type A or Type F RCD would be required instead.