What this MCCB delivers
The Siemens SENTRON 3VA1120-4EF32-0KC0 is a 3-pole molded case circuit breaker (MCCB) rated for 20 A continuous at 40 °C, with a breaking capacity of 121 kA at 240 V AC — that's the figure that governs its ability to clear a bolted fault on a low-voltage distribution board without the arc flashing over to adjacent gear. At higher supply voltages the interrupting rating steps down: 75.6 kA at 415 V, 52.5 kA at 440 V, and 11.9 kA at both 500 V and 690 V. These numbers matter when you're coordinating downstream feeders in a 480 V or 600 V panel — the SCCR of the entire assembly is limited by the lowest-rated device in the fault path. The breaker carries a shunt trip (STL) as the auxiliary release and two HQ auxiliary switches, so it can be remotely tripped and its status fed back to a PLC or annunciator without a separate contactor block.
Thermal derating and panel fit
Rated current holds at 20 A from 40 °C up to 55 °C, then drops to 19 A at 60 °C and 65 °C, and stays at 19 A through 70 °C. That's a shallow derating curve — useful when the breaker sits in a crowded enclosure where ambient air temperature climbs above 40 °C. The maximum power loss is 12 W, which you'll want to account for in the enclosure's thermal budget. Physical footprint: 70 mm deep, 76.2 mm wide, 130 mm tall. Operating temperature range is -25 °C to 70 °C; storage range is -40 °C to 80 °C. Insulation voltage rated at 800 V.