What this MCCB is and where it lands
The Siemens 3VA1120-5EF42-0AA0 is a SENTRON-series 4-pole molded case circuit breaker (MCCB) rated for line protection — the front-line overcurrent device between the transformer or bus and a distribution sub-panel. It carries a TM240 thermal-magnetic release, meaning the thermal element handles overloads and the magnetic element clears short-circuits, no electronic trip unit, no communication, no ground-fault monitoring. At 240 V AC the interrupting capacity hits 187 kA; at 415 V it's 121 kA, at 440 V it's 75.6 kA, and at 500/690 V it holds at 17 kA. That curve tells you the breaker is built for high-fault locations — main distribution boards, transformer secondaries, or large motor control centers where available fault current is well above 100 kA.
Thermal rating and what it means for the panel
Rated current is 20 A and it holds that rating from 40 °C through 55 °C ambient without derating. At 60 °C it drops to 19 A, and it stays at 19 A through 70 °C. For a panel builder that means the breaker can sit in a warm enclosure — say a steel box with VFDs or transformers nearby — and still deliver its full 20 A up to 55 °C. Above that you lose 1 A. The power loss at rated load is 12 W, which is modest for a 4-pole MCCB and won't drive a significant temperature rise inside a well-ventilated panel. Insulation voltage is rated 800 V, so the breaker is comfortable on 480/277 V or 600 V systems with margin.
Physical fit and panel integration
Dimensions are 130 mm high, 101.6 mm wide, 70 mm deep. The 101.6 mm (4-inch) width for a 4-pole breaker is standard for the SENTRON 3VA frame size — it occupies the same footprint as other 4-pole 3VA breakers in the same current range, so a panel laid out for a 3VA125 or 3VA111 will accept this unit without re-drilling the mounting plate. Front IP40 means it's protected against tools and wires >1 mm but not against water ingress; keep it inside a closed enclosure.