The 1200 A frame means it's sized for main feeders or large downstream distribution — not branch circuits. The ETU350 gives you adjustable long-time, short-time, instantaneous, and ground-fault protection curves, so selectivity with downstream breakers is configurable, not fixed. The interrupting ratings tell you where this breaker can sit on the fault-current map: 187 kA at 240 V, 121 kA at 415 V and 440 V, 75.6 kA at 500 V, and 3 kA at 690 V. That's unusual — most MCCBs start derating above 40 °C. For a panel running hot near the top of a NEMA 12 enclosure, this part holds its rating without a correction factor.
Integration and panel fit
The 105 mm width is a 4-pole-module footprint on a standard DIN-rail or panel-mount backplate — three poles plus neutral if you need it, though this unit ships as a 3-pole only. Depth of 86 mm means it fits most standard distribution enclosures without a deep-can extension. The breaker includes a shunt trip (STL) as the auxiliary release, plus one auxiliary switch and one trip-alarm switch (HP). The basic switch is order code 3VA20105HN320AA0 — if you're replacing just the switch mechanism, that's the spare part number. Maximum power loss is 13.5 W — negligible for thermal budget in most panels, but worth noting if you're packing multiple breakers in a sealed enclosure.
What the ETU350 trip unit gives you
The ETU350 is an electronic trip unit with adjustable LSI protection: long-time pickup and delay (Ir, tr), short-time pickup and delay (Sd, tsd), and instantaneous pickup (Ii). It also includes ground-fault protection (Ig, tg). The '350' tier is the mid-range electronic trip — above basic thermal-magnetic but below the full communications-enabled ETU600. No communication function on this variant, so no Modbus or PROFIBUS interface built in. Trip indicator and voltage trigger are present, so you get a local mechanical flag and can interface with external undervoltage or shunt-trip circuits. No undervoltage release fitted as standard — that's a separate accessory if needed.