What it is and what it does
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. It is rated 40 A at 30 °C with a C tripping characteristic, meaning it handles moderate inrush from motor or lighting loads without nuisance trips. The type A residual current detection covers pulsating DC fault currents, common on single-phase electronics and rectified loads.
Breaking capacity and standards
Rated breaking capacity is 6 kA per EN 60898 and 10 kA per IEC 60947-2. The EN 60898 figure governs residential and light commercial distribution boards; the IEC 60947-2 figure applies when the device is used in industrial panels where higher prospective fault currents are expected. 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. Terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm², covering most branch-circuit wiring sizes.
Mounting and integration
Occupies 2 width units (36 mm) on a DIN rail. Installation depth is 70 mm; overall depth 77 mm. 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).