The 40 A rating holds only at 30 °C ambient. At 40 °C it derates to 37.6 A; at 50 °C to 34.8 A; at 55 °C to 32.4 A. Above 55 °C the operating limit is 55 °C ambient, so the 32.4 A at 55 °C is the practical ceiling for a warm enclosure. The 15.6 W maximum power dissipation matters when packing multiple RCBOs in a distribution board — that heat has to leave the panel, or you derate further. The 70 mm installation depth plus 77 mm overall depth means it fits standard 80 mm deep enclosures with a few mm to spare for wiring.
Wiring and mounting — what fits
Terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm² — that covers everything from 1.5 mm² lighting circuits up to 10 mm² feeders for a 40 A load. Mounting position is any orientation, so vertical or horizontal DIN-rail installation is fine. The IP20 rating applies only when the distribution board is installed with conductors connected — it is not a standalone outdoor device.