What the 225 A TMF rating means for panel fit
The XT3NU3225AAA000XXX: The 225 A frame size with a TMF trip unit covers motor and feeder protection in the 160–225 A range. The thermal element handles overloads with an inverse-time curve; the magnetic element provides instantaneous short-circuit protection. For a panel OEM or MRO planner, this means the breaker coordinates with downstream contactors and overload relays in a standard motor branch circuit — no separate electronic trip module to power or configure.