400 A MCCB with ETU850 — what the ratings mean for panel fit
The Siemens SENTRON 3VA2340-5KP42-0AL0 is a 4-pole molded case circuit breaker rated for 400 A continuous current at 40 °C, carrying the full 400 A up to 50 °C before derating begins — at 55 °C it holds 375 A, at 70 °C it holds 300 A. That thermal profile means this breaker can sit in a warm enclosure without stepping down a frame size, as long as the ambient inside the panel stays under 50 °C. The ETU850 electronic trip unit handles the overcurrent protection logic. It is a line protection version — meaning it is set up for feeder protection rather than motor or generator duty — and it communicates, so you get trip data and status back to the control system without separate aux contacts. Breaking capacity is 187 kA at 240 V, 121 kA at 415 V, 55 kA at 440 V, 36 kA at 500 V, and 7.5 kA at 690 V. At typical 400 V class distribution voltages, that 121 kA rating covers high-fault locations like substation feeders or large bus risers without needing a current-limiting upstream breaker. Dimensions are 110 mm deep, 184 mm wide, 248 mm tall — a standard 4-pole MCCB footprint that fits Siemens SENTRON mounting accessories and busbar systems. The auxiliary contact configuration includes 2 auxiliary switches, 1 trip alarm switch, and 1 electrical alarm switch (HQ type), giving full status feedback for PLC or SCADA monitoring.
Panel integration — what the specs mean for the wireman
Mounts on a standard DIN rail or direct to the backplate using the SENTRON mounting base. The 184 mm width fits a 4-pole MCCB slot in a typical Siemens panelboard or standalone enclosure. Rated insulation voltage is 800 V, so it is suitable for 690 V systems with margin. Power loss is 96 W maximum at rated current — that is the heat the enclosure must dissipate. In a sealed cabinet, factor that into the thermal calculation alongside other devices. Operating temperature range is -25 °C to 70 °C; storage range is -40 °C to 80 °C.