400 A MCCB with ETU350 — what the ratings mean for the panel
The Siemens SENTRON 3VA2440-6HN32-0DH0 is a 3-pole molded case circuit breaker rated for 400 A continuous current (Iu) with an 800 V insulation voltage (Ui). That 400 A holds flat from 40 °C up to 50 °C, then derates to 384 A at 55 °C and 360 A at 70 °C — so in a warm enclosure you still have most of the rating. The ETU350 electronic trip unit gives you adjustable overload and short-circuit protection curves, not just a fixed thermal-magnetic snap. Breaking capacity is 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 187 kA at 415 V is the figure most plant distribution systems care about for high-fault bus work. This version ships with an undervoltage release (UVR) built in — part number 3VA9608-0BB25 for the release module itself. The auxiliary contact block is a 2-switch plus 1 trip-alarm configuration (HQ type), so you get two form-C aux contacts and a separate alarm contact that changes state only on a trip event, not on manual open. Latching endurance is rated at 15,000 cycles, which is typical for a 400 A frame used in main or feeder duty — not for frequent switching, but for protection where the breaker stays closed most of the time.
Panel fit — dimensions and mounting
The breaker measures 138 mm wide, 248 mm tall, and 110 mm deep. That 138 mm width is the 3-pole frame footprint — it occupies three 45 mm module positions on a standard DIN rail or panel-mount backplate. The 110 mm depth includes the rotary handle and rear terminals; allow clearance for cable bending radius below the line and load lugs.
Power loss and thermal management
Maximum power dissipation is 66 W at rated current. That matters for enclosure sizing — a 400 A MCCB dumping 66 W into a sealed cabinet needs ventilation or derating if the ambient inside hits 55 °C or higher. The derating curve from the spec table shows the breaker loses 40 A between 50 °C and 70 °C, so panel builders should place it away from other high-heat devices or provide forced airflow.