That 400 A holds flat from 40 °C up to 50 °C; above that it derates to 384 A at 55 °C, 376 A at 60 °C, 368 A at 65 °C, and 360 A at 70 °C — so if this lands in a hot panel near a drive or transformer, the 50 °C threshold is the one to watch. Breaking capacity runs 187 kA at 240 V, drops to 121 kA at 415 V and 440 V, then 75.6 kA at 500 V, and 17 kA at 690 V.
Motor protection build — what's inside and what's not
This is the motor protection version, meaning the ETU350M trip unit includes phase failure detection and a trip indicator. Power loss maxes at 63.5 W — that's the heat the breaker dumps into the enclosure. In a multi-breaker lineup, that figure drives the ventilation or derating calc for the surrounding units.
That 138 mm width for a 3-pole 400 A frame is standard for SENTRON 3VA — it fits the same mounting footprint as other breakers in the series, so swapping from a lower-rated unit doesn't require drilling new holes or reworking the bus bars. Keep it in a dry indoor panel. The storage low end matters if this sits in an unheated warehouse before installation.