What this RCBO is and what it does
The Siemens SENTRON 5SU1356-0KK40 is a 2-pole (1P+N) residual current operated circuit breaker (RCBO) combining overcurrent protection and residual current detection in a single 36 mm wide (2 modular width units) device for 50 Hz systems. Rated 40 A at 30 °C with a Type B tripping characteristic, it interrupts overcurrents per EN 60898 up to 6 kA and per IEC 60947-2 up to 10 kA, with a residual current type AC (sinusoidal) — suited for general-purpose final circuits in residential and commercial distribution boards. The RCBO mounts in any position, accepts supply from either top or bottom, and carries an IP20 rating once installed in a distribution board with connected conductors.
Temperature derating — what the 40 A rating actually means in a warm panel
The 40 A rating is at 30 °C ambient. At 40 °C the continuous current drops to 37.6 A, at 50 °C to 34.8 A, and at 70 °C to 29.2 A. If the distribution board sits in a warm environment or is tightly packed, size the load side accordingly — the nameplate 40 A is not the usable figure at elevated panel temperature.
Panel integration and physical fit
Width of 36 mm (2 MW), depth of 77 mm, and installation depth of 70 mm. Fits standard DIN-rail distribution boards; the 70 mm installation depth means it clears most domestic and light commercial enclosure depths without modification.