Thermal derating — what the ambient-temperature table means for panel loading
The 20 A rating holds only at 30 °C. At 40 °C the RCBO is rated 18.8 A; at 50 °C it drops to 17.4 A; at 60 °C it is 16.2 A; at 70 °C it is 14.6 A. If the distribution board runs warm — say 50 °C inside the enclosure — the circuit must be loaded to no more than 17.4 A continuous. This is the figure a panel builder uses for conductor sizing and load scheduling, not the 30 °C number.
The 5SU1654-0KK20 occupies 2 modular width units (36 mm) on a DIN rail, with a depth of 77 mm and an installation depth of 70 mm. Height is 90 mm. Supply can enter from either top or bottom — no mandatory orientation. Halogen-free and silicon-free construction means the RCBO won't outgas corrosive compounds in a sealed enclosure or near sensitive electronics.