The Siemens SENTRON 5SM2343-6 is a 4-pole residual current device (RCD) rated 40 A at AC with a 30 mA trip threshold, Type A (pulsating DC and AC sensitive), instantaneous trip, for 50 Hz networks. It's designed for 4-wire systems — three phases plus neutral — and fits the standard 3-module-width DIN-rail cutout in a distribution board. The 30 mA trip covers general socket-outlet and lighting circuits where personnel protection is required; Type A sensitivity catches the rectified DC fault currents that older AC-only RCDs miss.
Width is 123 mm (3 MW), depth 70 mm, height 90 mm. That's the standard SENTRON 4-pole RCD footprint — it clips onto the same DIN rail as the 5SL4 MCBs it's designed to pair with (the 'for 5SL4' variant note means the busbar and comb profile match directly). The IP20 rating applies when the board is closed; the device itself is not sealed for washdown.
The 40 A rating holds at 40 °C ambient (37.2 A derated at 40 °C per the spec). At 45 °C it's still 37.2 A; at 50 °C it drops to 36 A; at 55 °C to 34.8 A; at 60 °C to 34 A; at 65 °C to 33.2 A; at 70 °C to 32 A.