What this RCCB is and what the ratings mean for fit
The Siemens 5SM3644-6BA is a 4-pole RCCB from the SENTRON 5SM3 series, rated 40 A and 300 mA trip threshold. Type A detection responds to sinusoidal AC and pulsed DC residual currents. The rated supply voltage is 400 V AC. The 4-pole design switches three phases and neutral. Mounting on DIN rail with 4-module width and 70 mm installation depth fits standard distribution boards.
Installation and wiring constraints
Terminals accept solid or stranded conductors from 1.5 mm² up to 25 mm², covering most branch-circuit feeder sizes up to the 40 A rating. Tightening torque is specified at 2.5 to 3 N·m — use a torque screwdriver; under-torquing raises contact resistance on a 40 A continuous load. Mounting position is unrestricted, and supply can enter from top or bottom, which simplifies busbar routing in crowded enclosures. The IP20 rating applies only with the distribution board installed and conductors connected — the RCCB itself is not touch-safe when removed from the enclosure. Ambient temperature range is -25 to +45 °C operating, -40 to +75 °C storage. Overvoltage category III means it is rated for fixed-installation downstream of the main distribution board, not for direct utility connection.