What this 400 A MCCB carries
The Siemens 3VA2340-6JQ32-0AC0 is a SENTRON 3VA2 molded case circuit breaker rated for 400 A continuous current (Iu) across a 40 °C to 50 °C ambient — no derating needed up to 50 °C. At 55 °C it holds 375 A, at 60 °C it holds 350 A, at 65 °C it holds 325 A, and at 70 °C it holds 300 A, so the thermal margin is generous for a 40 °C panel but you lose 100 A if the enclosure hits 70 °C. Breaking capacity runs 242 kA at 240 V, 187 kA at 415 V and 440 V, 121 kA at 500 V, and 40 kA at 690 V — that is a high-fault rated frame for tough industrial feeds. It is a 3-pole line protection version fitted with the ETU560 electronic trip unit. The insulation rating is 800 V Ui. Communication function is built in. The auxiliary contact version is 2 HQ switches, and it ships with a summation-current ground-fault monitoring scheme on the L-conductor.
Dimensions: 248 mm height, 138 mm width, 110 mm depth. Rated insulation voltage 800 V and rated impulse withstand voltage typical for the class. The ETU560 trip unit is field-replaceable and supports LSIG protection profiles. Maximum power loss is 96 W — enough heat that the enclosure needs ventilation or forced cooling if multiple breakers are ganged.