The Siemens 3VA4120-5ED14-3AA0 is a 1-pole circuit breaker in the 3VA4 UL Frame 125 series, rated 20 A with a 35 kA interrupting capacity at 277 V (class M). The thermal-magnetic trip unit (TM210) has the overload protection Ir permanently set at 20 A, and the short-circuit protection Ii is fixed at 15 x In — no field adjustment for either. This is a made-to-order unit (product class C), so expect a build-to-order lead time; it is not a stocked shelf item.
What the ratings mean for fit
The 35 kA breaking capacity at 277 V tells you this breaker can safely interrupt a fault current up to that level on a 277/480 V wye system without welding contacts or venting plasma. It is sized for line-side protection on a single-phase branch or a 277 V lighting circuit. Because Ir and Ii are both fixed, there is no dial to tweak — you select the breaker for the exact load current and let the thermal curve handle overloads. The 3VA4 frame is a UL 489 listed miniature circuit breaker, so it fits standard panelboard and load-center mounting. The 1-pole form factor occupies one 18 mm module on the DIN rail. For a 20 A continuous load on a 277 V circuit, this is a direct drop-in replacement for any existing 3VA4 or comparable UL 489 breaker with the same frame and trip setting.