D-curve means the magnetic trip is set to 10–20× In — it holds through the inrush of a small motor or power supply that would pop a B or C curve. The 3 A rating is at 30 °C; at 40 °C it derates to 2.88 A, at 45 °C to 2.82 A, and at 55 °C to 2.69 A. The 72 V DC maximum rating is for the DC side — useful if this breaker is used in a DC subdistribution, but the primary application is AC.
IP20 with connected conductors — dry indoor panels only, not washdown. Sealable, halogen-free, silicon-free — relevant for clean-room or low-smoke installations. Ambient range -40 to 75 °C with max 95% humidity at 55 °C.