What the 320 A TMA trip means for fit
The TMA designation indicates a thermal-magnetic trip — the thermal element protects against sustained overloads (cable heating, moderate overcurrents), while the magnetic element handles short-circuit faults with instantaneous response. The 320 A rating sets the continuous current limit; for motor or transformer feeder applications, size the upstream cable and downstream load so the full-load current stays below this threshold. The T5N400 frame carries a 400 A maximum frame rating, so this breaker is a 320 A fixed-trip variant within that frame — no interchangeable trip units, which simplifies BOM but locks the rating.
Panel and deployment context
In a distribution panel, it occupies a single module width for the frame size. The fixed thermal-magnetic trip means no field adjustment of the current setting — specify the exact 320 A rating at the design stage. For selective coordination studies, the TMA trip curve data is available from ABB's documentation set.