Siemens 3VA1140-4EE42-0AA0 SENTRON MCCB, 40A 4-Pole, 121kA a

Breaking capacity runs 121 kA at 240 V AC, 76 kA at 415 V, 53 kA at 440 V, and holds 11.9 kA all the way out to 690 V; that curve tells you it's sized for high-fault industrial distribution where available fault current varies by transformer tap and voltage class. Temperature derating is honest: it carries the full 40 A from 40 °C through 50 °C, drops to 39 A at 55–60 °C, then 38 A at 65 °C and 37 A at 70 °C. That means in a sealed, uncooled enclosure near other heat sources you lose about 7.5 % of capacity at the top end — plan your load accordingly rather than assuming nameplate current holds at every ambient.