The Siemens SENTRON 5SU9356-7KM40 is an RCD-operated circuit breaker (RCBO) combining overcurrent protection and residual current detection in a single 2-module (36 mm wide) package. The type A residual current detection covers pulsating DC fault currents, common on single-phase electronics and rectified loads.
Breaking capacity and standards
Overvoltage category III confirms suitability for fixed installation downstream of the utility meter.
Thermal derating and conductor sizing
Rated current of 40 A at 30 °C derates to 37.6 A at 40 °C, 36.4 A at 45 °C, 34.8 A at 50 °C, and 32.4 A at 55 °C. In a 40 °C panel — typical for enclosed distribution boards — the effective continuous current is 37.6 A, so size the downstream load accordingly.
Mounting position any, supply feed either top or bottom. IP20 with connected conductors in an installed distribution board — standard for enclosed panel use. Halogen-free and silicon-free construction suits environments sensitive to corrosive off-gassing (data centers, medical facilities).