What this breaker does and where it fits
The Siemens 3VA4120-4ED14-3AA0 is a 1-pole molded-case circuit breaker from the 3VA4 UL Frame 125 family, rated 20 A continuous with a fixed overload setting (Ir = 20 A) and a short-circuit pickup of 15 × In (300 A). Its interrupting capacity is 25 kA at 277 V, placing it in the S (standard) breaking capacity class — enough for most commercial and light-industrial panelboard feeders where fault current stays under that threshold. The TM210 thermal-magnetic trip unit provides line protection: the thermal element handles overloads, the magnetic element clears short-circuits. The FTFM (Fixed Thermal, Fixed Magnetic) design means both Ir and Ii are permanently set — no field-adjustable dials, no calibration drift. For a BOM line, this simplifies specification: what you order is what protects the circuit, every shot the same. The 3VA4 UL Frame 125 accepts plug-in accessories (auxiliary contacts, shunt trip, undervoltage release) that share the same mounting footprint across the frame size. If the panel design already uses 3VA4 breakers, this unit drops into the same DIN-rail adapter or screw-mount base without re-drilling the backplate.
Lifecycle and sourcing posture
Export control is straightforward: AL: N / ECCN: EAR99 — no special licensing required for most destinations. RoHS compliant since May 2019; REACH Article 33 disclosure applies for lead (CAS 7439-92-1) above 0.1% w/w, which is typical for electrical contacts and solder joints in this class of breaker.
What the ratings mean for the buyer
The 25 kA interrupting capacity at 277 V is the breaker's ability to safely clear a fault without welding contacts or rupturing the case. In a 277/480 V panel, this covers most branch circuits fed from a transformer up to about 150 kVA — enough for lighting panels, small motor control centers, and HVAC equipment. If the available fault current at the panel exceeds 25 kA, a current-limiting upstream fuse or a higher-rated frame (3VA4 S class at 35 kA or H class at 65 kA) would be needed for coordination. The fixed 15 × In short-circuit pickup (300 A for this 20 A unit) means the magnetic trip will not nuisance-trip on motor inrush or capacitor charging currents that stay below that multiple. For a circuit feeding a 20 A resistive load or a small motor with a nameplate FLA under 16 A, this pickup provides adequate protection without false trips.