What it is and what it does
The Siemens 3VA4120-4ED24-3AA0 is a 2-pole molded case circuit breaker from the 3VA4 series, built on a UL Frame 125 platform. It's rated for 20 A continuous with a 25 kA interrupting capacity at 480 V — that's the 'S' breaking capacity class, which means it handles standard commercial and light industrial fault levels without cascading upstream. The TM210 trip unit gives you fixed thermal-magnetic protection: Ir is permanently set at 20 A for overloads, and the magnetic short-circuit pickup (Ii) is locked at 15× In, or 300 A. No field-adjustable dials on this one — what you order is what protects your circuit.
Where it fits in a panel
This breaker mounts on a DIN rail in a standard UL 508A panel. The 2-pole footprint takes up one module width per pole, so plan for two 18 mm slots. Line and load lugs accept copper or aluminum conductors — torque per the label on the front. Because it's a fixed-trip TM210, there's no rotary dial to accidentally bump during commissioning; what's set at the factory stays set.