Spec recap and fit
The Siemens 3VA1120-5ED12-0AA0 is a 1-pole SENTRON molded case circuit breaker (MCCB) rated for 20 A continuous current (Iu) with a TM210 thermal-magnetic release. Its interrupting capacity hits 121 kA at 240 V AC and 9 kA at 415 V AC — the 240 V figure covers most North American panelboard fault duties, while the 415 V rating confirms it for 400 V-class European distribution. The 25.4 mm width (1 in) and 70 mm depth (2.8 in) mean it snaps onto a standard DIN rail with one module of space — no special adapter needed. The 130 mm height (5.1 in) fits within typical enclosure clearances for a single-pole breaker. Rated insulation voltage Ui is 500 V, maximum DC operational voltage is 250 V. Short-circuit pickup (Ii) is fixed at 320 A.
Thermal derating and enclosure
The breaker holds its full 20 A rating from 40 °C up to 55 °C ambient. At 60 °C it derates to 19 A, and at 70 °C it's still 19 A — no steep cliff. That's a wide thermal plateau, useful in a sealed enclosure with other heat sources. Maximum power loss is 4 W at rated current, so internal heating from the breaker itself is negligible. Front IP40 protection means the breaker face is splash-proof against tools and dust ingress, but the enclosure must still provide overall IP rating for the panel. Storage range spans -40 °C to 80 °C, operating range -25 °C to 70 °C.