The Siemens 5SU1354-0KV40 is a combined residual-current and miniature circuit breaker (RCBO) — an FI/LS-Protector Type AC (WS) in a 1+N-pole form factor. It integrates 30 mA earth-leakage protection with a B-curve overcurrent trip rated at 40 A, all in a 70 mm-wide housing that snaps onto a standard DIN rail. The 10 kA breaking capacity (IEC 60898) means it can safely interrupt fault currents up to that level in a 230/400 V AC installation without upstream damage.
The 30 mA sensitivity (IΔn) is the standard threshold for personal protection against direct-contact shock in residential and commercial final circuits. The B-curve (40 A) trips between 3 and 5 times rated current, suited for resistive and general-purpose loads with modest inrush — lighting, socket outlets, small appliances. The 10 kA breaking capacity covers most distribution board fault levels; for higher prospective fault currents, a current-limiting upstream MCB or fuse is required.