The interrupting capacity hits 187 kA at 240 V, 121 kA at 415 V and 440 V, and 79 kA at 500 V — numbers that tell you this breaker is sized for high-fault industrial distribution, not light commercial panels. The ETU350 is a basic electronic trip unit — no voltage trigger, no phase-failure detection, no communication module. It handles line protection (overload and short-circuit) with a fixed thermal-magnetic curve. Temperature derating is modest: the breaker holds 63 A from 40 °C through 50 °C, then drops to 60.6 A at 55 °C, 58.3 A at 60 °C, 55.9 A at 65 °C, and 53.6 A at 70 °C.
The 63 A rating at 40–50 °C without derating is the headline number for feeder or main breaker duty. At 415 V (common European distribution voltage), 121 kA still covers virtually all utility-transformer fault levels. The ETU350 trip unit is a basic electronic unit — it gives you adjustable thermal and magnetic settings but lacks the communications, ground-fault, or voltage-based protection of higher-tier ETU units. If your spec calls for Modbus monitoring or ground-fault alarm, this isn't the variant; you'd step up to a 3VA2 with ETU600 or ETU800.