The Siemens 5SU9106-1DV40 is a combined residual current device and miniature circuit breaker (RCBO) in a single 1+N-pole module. It provides both earth leakage protection and overcurrent/short-circuit protection in one DIN-rail mounted unit, saving panel space over separate RCD and MCB devices. The Type AC designation means it detects sinusoidal AC residual currents only — standard for general-purpose socket circuits and lighting loads where no rectified or pulsed DC fault currents are expected. Rated at 40A with a C-curve trip characteristic (5-10x In for magnetic release), it suits inductive loads like small motors, fluorescent lighting banks, and pump starters where moderate inrush is expected. The 30mA residual sensitivity provides personal protection against direct contact for socket-outlet circuits per IEC 60364.
The 40A rating at 30°C ambient is the continuous current the device can carry without tripping its thermal element. The C-curve means the magnetic trip operates between 200A and 400A (5-10x In) — this avoids nuisance tripping from motor starting currents while still clearing hard faults. The 1+N-pole construction switches both phase and neutral, but the neutral pole is not protected against overcurrent — only the phase pole has the thermal-magnetic trip.