What this 400 A molded-case breaker does
The ABB XT5HQ340AEFF000XXX is a 3-pole molded-case breaker rated 400 A continuous at 600 VAC, built on the XT5H frame and fitted with an EKIP DIP LS/I electronic trip unit. The 400 A frame means the breaker body itself is sized for that current — no adapter needed for a 400 A feed. The EKIP DIP LS/I provides LS/I protection (long-time and short-time delay plus instantaneous), giving you adjustable pickup and time bands for coordinating with downstream feeders or motor loads. At 600 VAC it covers the common 480 V and 600 V distribution voltages in North American industrial panels without derating.
What the 400 A rating means for fit
It is not a motor full-load current; for a motor branch circuit you would size the breaker per the NEC motor tables, typically 250 % of FLA for an inverse-time breaker. On a 480 V feeder feeding a 400 A continuous load, this breaker holds without nuisance tripping. The EKIP DIP LS/I trip unit lets you dial in the long-time pickup (typically 0.4–1.0 × In) and short-time delay to coordinate with downstream breakers, so you can clear a fault at the branch without taking out the main.
The 3-pole configuration accepts three line conductors and three load conductors; the neutral is not switched. Wire range for the line and load terminals typically accepts up to 500 kcmil copper or aluminum — verify the lug kit if the install uses aluminum conductors. The EKIP DIP LS/I trip unit is front-accessible for adjustment without removing the cover, so you can set the long-time and short-time bands after installation.