The XT3NU3100AFF100XXX: The TMF trip designation means the breaker uses a thermal-magnetic mechanism: the thermal element provides inverse-time overload protection for conductor and load heating, while the magnetic element delivers instantaneous short-circuit response. The 100-1000 A range on the trip unit indicates an adjustable magnetic pickup — the 100 A setting is the nominal continuous current rating, but the instantaneous trip threshold can be dialed up to 1000 A to coordinate with downstream devices or motor inrush. The 225 A frame means the breaker's physical housing and contacts are rated for up to 225 A, so the 100 A trip can be swapped for a higher-rated trip unit later without replacing the entire breaker.
Molded case circuit breakers in the XT3N family are panel-mounted devices used for branch-circuit protection in industrial switchboards, motor control centers, and distribution panels. The UL/CSA listing qualifies it for North American installations under NEC and CEC. The 3-pole configuration suits three-phase loads — motors, transformers, feeders — where all three phases must be simultaneously disconnected on a fault.