What the ratings mean for fit
The XT4NU3225FFJ000XXX: The 225 A rating on the EKIP LSI trip unit covers the L (long-time), S (short-time), and I (instantaneous) protection curves — the standard set for feeder and main breaker applications where you need adjustable short-time delay for selective coordination downstream. The XT4N 250 frame physically accommodates this trip rating with headroom to 250 A if you ever re-rate. The 3-pole configuration suits three-phase systems; the F designation indicates fixed (non-interchangeable) trip units, so the protection settings are factory-set for the 225 A rating.