The Siemens 5SU1353-1KV40 is a combined residual-current device and miniature circuit breaker (RCD/MCB) — an FI/LS protector in the 5SU series. It combines Type AC earth-leakage detection with overcurrent protection in a single 1+N-Pole module, rated C 40 A, with a rated residual current of 30 mA and a short-circuit breaking capacity of 4.5 kA.
The 30 mA sensitivity is the threshold for personal protection against direct contact (IEC 60364 mandates 30 mA for circuits supplying socket outlets up to 20 A). The C 40 A characteristic handles moderate inrush loads like small motor starters and lighting banks without nuisance tripping, while the 4.5 kA breaking capacity covers the prospective fault current at the point of installation in most domestic and small commercial distribution boards.