That LI protection curve (long-time + instantaneous) covers branch circuits where you need overload protection with a fast magnetic trip on hard faults. Rated 20 A continuous from 40 °C through 55 °C, then derates to 19 A at 60 °C and 18 A at 70 °C. That flat thermal band means you don't lose headroom until the panel ambient climbs above 55 °C — useful in a crowded enclosure with limited airflow. The interrupting ratings are the headline: 150 kA at 120 V, 65 kA at 277 V, and 25 kA at 347 V. At 25.4 mm wide (1 inch), it packs into a single-pole module on the DIN rail. Depth is 75.1 mm, height 129.4 mm — standard SENTRON 3VA footprint, so it swaps into existing panels without re-drilling gland plates.
The 25.4 mm width means it occupies exactly one 1-inch module — no overhang, no filler pieces needed. Terminal layout is standard for the 3VA family: line on top, load on bottom, with the TM210 release dial accessible from the front for the magnetic pickup adjustment.