What this MCCB is and what it protects
The Siemens SENTRON 3VA1120-3EF36-0KA0 is a 3-pole molded case circuit breaker rated for 20 A continuous current at 40 °C, with a TM240 thermal-magnetic overcurrent release. It is configured as a line protection device — meaning its trip curve and interrupting rating are tuned for feeder and distribution circuits, not motor starting duty. The 75.6 kA breaking capacity at 240 V AC gives it the headroom to sit upstream of smaller branch breakers in a high-fault panel, so you can coordinate selectivity without stepping up to a larger frame.
Breaking capacity across voltages — where this fits in a distribution scheme
This breaker delivers 75.6 kA at 240 V, 52.5 kA at 415 V, 32 kA at 440 V, and 10.5 kA at 690 V. The steep drop at 690 V is typical for a 20 A frame — the arc extinction limits on a higher-voltage fault. If your panel feeds a 690 V bus, verify that 10.5 kA exceeds the available fault current; otherwise step to a higher-rated 3VA variant. At 415 V, 52.5 kA covers most industrial switchboards without requiring a current-limiting upstream breaker.
Thermal derating — the real current you can run
The 20 A rating holds flat from 40 °C through 50 °C. Above that it derates: 19.2 A at 55 °C, 18.8 A at 60 °C, 18.4 A at 65 °C, and 18 A at 70 °C. If this breaker lives in a sealed enclosure near transformers or drives, use the 70 °C figure (18 A) for your continuous load calculation — the thermal-magnetic release responds to internal heat, and a hot panel will trip earlier than the nameplate suggests.