Interrupting capacity is 187 kA at 240 V, 121 kA at 415 V and 440 V, 75.6 kA at 500 V, and 7.5 kA at 690 V.
The 138 mm width is a 3-pole frame; it occupies three adjacent 45 mm DIN-rail positions. IP40 on the front face means no gasket seal against the door; the breaker vents into the enclosure, so account for heat dissipation (37.5 W max power loss at rated load) in the panel thermal budget.
Most MCCBs in this frame size start derating above 40 °C; this one doesn't, which means you can size the breaker to the load without adding a temperature-correction factor for a hot panel. The ETU350 release gives selectivity coordination flexibility — adjustable I²t on short-time delay lets you coordinate downstream breakers without sacrificing speed on a hard fault.