It carries a 121 kA breaking capacity at 240 V AC, stepping down to 75.6 kA at 415 V and 52.5 kA at 440 V — numbers that tell you this breaker handles high-fault panels without cascading upstream. An integrated undervoltage release (UVR) means it can drop the load on loss of control power, which is what you want on a safety-critical feeder or a motor control center.
The 40 A rating holds flat from 40 °C to 50 °C — no derating in a warm enclosure — then eases to 39 A at 55–60 °C and 37 A at 70 °C. That thermal curve matters when you're packing breakers side-by-side in a switchboard. The 121 kA at 240 V is the headline interrupting rating; the 75.6 kA at 415 V is what you coordinate against downstream devices in a 400 V distribution board.
Footprint: 76.2 mm wide (3 in), 130 mm tall (5.12 in), 70 mm deep (2.76 in). It ships with two auxiliary switches (HQ design) and the undervoltage release pre-integrated — no extra wiring for the UVR coil if you're already running a control voltage. Power loss maxes at 13.3 W, so heat buildup in a dense lineup is manageable.