The SENTRON 3VA1332-5EF32-0CJ0 is a 3-pole molded case circuit breaker (MCCB) rated 320 A at 40 °C, with a TM240 thermal-magnetic overcurrent release and an integrated undervoltage release.
Full rated current of 320 A holds from 40 °C through 50 °C, then derates linearly to 292 A at 70 °C. That means a panel builder can size this breaker into a 50 °C enclosure without a current penalty — useful in tightly packed switchgear where internal ambient runs high. Breaking capacity drops with system voltage: 187 kA at 240 V, 121 kA at 415 V and 440 V, 75.6 kA at 500 V, and 11.9 kA at 690 V.
The 138 mm width is the 3-pole frame — verify your panel's pole spacing if retrofitting into an existing MCC bucket. Maximum power loss is 82.6 W, so account for that heat in your enclosure's thermal calculation.