The ABB XT5NU440ATFF000XXX is a 400 A breaking part for the XT5N molded-case circuit breaker platform, configured as a 4-pole unit with F F (front-front) terminations and UL/CSA+TU certification. This is a field-replaceable internal subassembly — the breaking part carries the arc chambers, contacts, and trip mechanism that actually interrupt fault current. It is not a standalone breaker; it mounts inside the XT5N frame during assembly or as a service replacement when the original interrupting module is damaged or needs a different rating.
What the approvals tell you
The UL/CSA+TU marking on this breaking part means it carries UL and CSA certification for the North American market, plus TU (Technischer Überwachungsverein) approval for the German and broader European market. That dual certification simplifies panel builds that need to satisfy both IEC and NEC code requirements — one part number covers both jurisdictions.