Rated 20 A at 40 °C ambient, and it holds that rating through 55 °C. At 60 °C it derates to 19 A, and at 70 °C it is still 19 A — so in a warm panel (say 50 °C) you get the full 20 A without having to oversize the breaker.
Breaking capacity across voltages
Breaking capacity is 52.5 kA at 240 V AC, 32 kA at 415 V, 13.6 kA at 440 V, and 7.5 kA at both 500 V and 690 V. This is a high-interrupting-capacity (HIC) variant for the 20 A frame — it can handle fault currents that would weld a standard 10 kA MCCB on a 240 V secondary. At 690 V the 7.5 kA rating is still adequate for most industrial motor branch circuits, but verify against your transformer's impedance and available fault current.
Dimensions are 76.2 mm wide (3 in), 130 mm tall (5.12 in), and 70 mm deep (2.76 in).