The Siemens 5SU1644-1RC40 is a 40 A, 4-pole RCBO from the SENTRON family — a combined overcurrent and residual-current device that protects a three-phase circuit against overload, short-circuit, and earth leakage in one 7-module-wide unit. The Type AC 300 mA residual-current element detects sinusoidal AC fault currents down to 300 mA, which covers basic personnel protection and fire prevention on circuits without non-sinusoidal loads. Breaking capacity is 10 kA per EN 60898 and 15 kA per IEC 60947-2 — the higher figure under the industrial standard means it can interrupt a 15 kA prospective fault current on a 415 V AC supply without welding the contacts or cascading damage upstream. That 15 kA rating is the one to use for selectivity studies in an industrial panel. Operating frequency is 50 Hz only; this part is not rated for 60 Hz networks.
The 5SU1644-1RC40 snaps onto a DIN rail (EN 60715) and occupies 7 modular width units (MWU) — 126 mm of rail space.