At 45 mm wide and 97 mm deep, it occupies a standard 45 mm modular device footprint — one width unit on the DIN rail. The 119 mm height clears most 200 mm-deep enclosures with room for wiring ducts above and below.
The 3RV2321-1EC20 delivers 100 kA breaking capacity at 240 V AC and 400 V AC, and 100 kA at 500 V AC. At 690 V AC it still interrupts 6 kA. The 4 A continuous rating at 480 V and 600 V (and 4 A at 690 V) tells you this is for smaller motor loads — fractional-horsepower pumps, fans, conveyors up to about 3 hp at 575/600 V. The rated switching frequency of 15 operations per hour at AC-3 duty matches typical start-stop cycles for a compressor or a small conveyor; it is not sized for high-cycle jogging applications.
Terminals and wiring
No ground-fault or phase-failure detection built in; those functions are handled upstream or by the connected overload relay.