What this breaker is and what it handles
The ABB XT5NU360BBFF000XXX is a 600 A rated, 3-pole molded case circuit breaker (MCCB) from the XT5N family, fitted with a TMA (thermal-magnetic adjustable) trip unit adjustable from 600 to 6000 A. That puts it in the right range for feeder and large motor branch circuits in industrial distribution panels where fault currents aren't trivial.
The 600 A continuous rating governs the feeder conductor sizing and the bus bar ampacity upstream. The adjustable TMA trip — 600 to 6000 A — lets you dial in the instantaneous magnetic pickup to coordinate with downstream breakers or motor starters, which is the main tool for achieving selective coordination in a distribution panel. The FF (fixed front) terminal pattern is standard for panelboard mounting — it connects to bus bars or cable lugs, not plug-in bases.