The ETU320 electronic trip unit handles the overcurrent protection. That's a fixed-setting thermal-magnetic replacement — no dials to spin, no modules to swap. Set it and forget it, which is exactly what you want when a line-down call comes in and the panel builder is already on site.
That's a standard 3-pole MCCB envelope for a 40 A frame — it'll drop into most existing panel layouts without re-drilling the backplate or re-laying the bus bar. Power loss is only 1.2 W maximum — negligible for thermal budgeting inside a packed enclosure.
What it doesn't do
This is a straight line-protection breaker — no auxiliary gadgets. If you need those, you're looking at a different variant in the 3VA family. For a simple feeder or main breaker role, this keeps the wiring clean and the troubleshooting simple.