The Siemens SENTRON 5SM2643-6 is a 4-pole residual current device (RCD-unit) rated 40 A, 300 mA sensitivity, type A, for 400 V AC at 50 Hz. It is an instantaneous-trip design — no adjustable delay or fault current — intended for direct fault clearing in distribution boards. The 123 mm width and 70 mm depth (3 modular width units) fit standard SENTRON panel cutouts; mounting position is unrestricted.
The 400 V AC insulation voltage (Ui) and 4000 V surge withstand (overvoltage category III) qualify it for main distribution panels in commercial and industrial installations, pollution degree 2 environment.
The unit mounts via the standard REG fastening method — snap-on to DIN rail in any orientation. IP20 protection applies only when the distribution board is installed with connected conductors; the enclosure must provide the environmental seal.