The Siemens 3VA1120-6EF42-0AA0 is a SENTRON molded case circuit breaker (MCCB) rated at 20 A continuous current (Iu) with a 4-pole configuration and a TM240 thermal-magnetic release. Its headline breaking capacity hits 220 kA at 240 V — that is the short-circuit current it can safely interrupt at that voltage without welding contacts or cascading failure upstream. At 415 V it still holds 154 kA, and at 690 V it derates to 17 kA, so the spec you care about for your line voltage is the one at your actual operating level. This is a line-protection device (not a motor-protection or ground-fault version), designed for panel main or feeder duty where you need high fault-interrupting capability in a compact DIN-rail footprint — 101.6 mm wide, 130 mm tall, 70 mm deep. The 12 W maximum power loss matters for thermal budget inside a sealed enclosure; if you are packing multiple breakers side-by-side, derate per the 45–70 °C ambient curve (20 A flat to 55 °C, then 19 A from 60–70 °C).
What the ratings mean for fit
The TM240 release is adjustable: the thermal element tracks the 20 A frame rating, and the magnetic short-circuit pickup (li) is adjustable up to 320 A — that is 16x the rated current, giving you headroom to ride through motor inrush or transformer energization without nuisance tripping. The 800 V rated insulation voltage (Ui) means it is suitable for 480/277 V and 600 V systems with margin. IP40 on the front face is standard for panel-mounted breakers — dust-protected but not washdown-rated. No communication function or ground-fault monitoring on this variant, so if you need remote trip indication or GF protection, you are looking at a different option card or a different order code.