The 125 A rating holds flat from 40 °C to 50 °C, then derates to 120 A at 55 °C, 117.5 A at 60 °C, 115 A at 65 °C, and 112.5 A at 70 °C — so if your panel ambient runs hot, you lose about 10 % of the headline number by the time you hit 70 °C. That derating curve is the spec that decides whether this breaker holds a full 125 A feeder or needs to be upsized for a warm enclosure. Interrupting capacity is 121 kA at 240 V, 75.6 kA at 415 V, 52.5 kA at 440 V, and 11.9 kA at 690 V.
The 76.2 mm width fits Siemens SENTRON mounting plates and most DIN-rail adapters. Front protection is IP40 — sealed against tools and small wires, but not against washdown. Keep this behind a panel door in any wet or dusty environment.
Release and accessories — what's on board, what's not
The TM240 overcurrent release is a thermal-magnetic type — fixed thermal curve for overload, magnetic pickup for short-circuit. No electronic adjustment, no communication module, no phase-failure detection. No auxiliary contact version is included (without). No undervoltage release. No ground-fault monitoring. If your application demands any of those, you'll need a different variant or an external module.