What this MCCB is and what it does
The Siemens 3VA1120-5EF36-0AA0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection in distribution panels and industrial switchgear. Three poles, rated 20 A continuous at 40 °C through 55 °C, with a TM240 thermal-magnetic overcurrent release — meaning the thermal element handles overloads and the magnetic element handles short-circuits, no electronic trip unit. Breaking capacity reaches 187 kA at 240 V AC, 121 kA at 415 V, 75.6 kA at 440 V, and 17 kA at both 500 V and 690 V, so it can interrupt very high fault currents on low-voltage mains. The 800 V rated insulation voltage covers most 400/480 V systems with margin.
Thermal derating and panel fit
Rated 20 A from 40 °C to 55 °C ambient; at 60 °C and 65 °C it holds 19 A, and at 70 °C still 19 A — derating is minimal, so you can load it near the nameplate in a warm enclosure without recalculating. Power loss is 12 W maximum at rated load, which matters for heat buildup in a sealed panel. Dimensions are 130 mm high, 76.2 mm wide, 70 mm deep — a 3-pole MCCB footprint that fits standard Siemens 3VA panelboard and switchboard mounting patterns. IP40 on the front means protected against tools and wires >1 mm, but not against water ingress; install inside a suitable enclosure.