It is a 3-pole device with a supplied basic switch order code of 3VA2440-5MN32-0AA0, meaning this is the assembled, ready-to-install unit with the internal switching mechanism pre-integrated. The breaking capacity tells you where this breaker can safely interrupt a fault: 187 kA at 240 V, 121 kA at 415 V and 440 V, 75.6 kA at 500 V, and 9 kA at 690 V. This is the motor protection version, so it includes phase failure detection built in — no separate phase-monitoring relay needed for that function. The auxiliary release slot is empty, so if you need an undervoltage or shunt trip, that gets added separately.
The 138 mm width is the 3-pole footprint; if you are replacing an existing MCCB in a SENTRON or similar platform, check the mounting hole pattern against the existing base plate.
Power dissipation and thermal management
Maximum power loss is 63.5 W at rated current. For a 400 A breaker in a closed panel, that heat needs to be considered in the enclosure thermal calculation — it is not a trivial loss, and adjacent devices should not be packed tight without derating or forced ventilation.