The Siemens SENTRON 3VA2340-5HN42-0BL0 is a 4-pole molded case circuit breaker (MCCB) rated for line protection, carrying 400 A continuous current with no derating from 40 °C through 50 °C. At 55 °C it holds 385 A, at 70 °C it holds 340 A — the thermal curve is published, so panel ambient temperature drives the real ampacity, not the nameplate. 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. That 690 V figure is the limiting case for 3-phase systems above 480 V — verify the fault current at the service entrance against the 7.5 kA ceiling before specifying.
In a 55 °C panel — common in enclosed switchgear with multiple breakers — the usable current drops to 385 A, a 3.75 % reduction. At 70 °C it is 340 A, a 15 % reduction. The thermal derating curve is the selection gate, not the 400 A label. The interrupting capacity at 690 V is 7.5 kA — that is the weakest point on the voltage curve. If the available fault current at 690 V exceeds that figure, this breaker cannot clear it. For 480 V systems the 75.6 kA rating at 500 V is the relevant bound.
Dimensions: 248 mm height, 184 mm width, 110 mm depth. The 184 mm width on a 4-pole frame is the critical panel cut-out dimension — verify the backpanel gland plate or mounting plate has that clearance before committing the drill pattern. The UVR coil must see rated voltage to close; a drop-out below the holding threshold trips the breaker — plan the control transformer and UPS feed accordingly. Maximum power loss is 98.5 W at rated current. In a sealed, multi-breaker enclosure that heat must be evacuated — factor it into the thermal budget alongside the derating curve above.