What this MCCB carries — and where it lands
The Siemens SENTRON 3VA1120-5EF36-0AC0 is a 3-pole molded case circuit breaker rated 20 A continuous at 40 °C, with a TM240 thermal-magnetic trip unit. It holds an interrupting capacity of 187 kA at 240 VAC and 121 kA at 415 VAC — numbers that put it squarely in high-fault-duty distribution, not branch-circuit light duty. The insulation voltage is rated 800 V, so it can sit upstream of step-down transformers or on 690 V line sides where the 17 kA rating still holds. Two built-in auxiliary switches HQ come standard, saving a slot on the DIN rail for the next breaker.
Interrupting capacity — what the numbers mean for your panel
The 187 kA at 240 V is the headline number, but the 121 kA at 415 V is the one that matters for most industrial mains. At 440 V it still breaks 75.6 kA, and at 500 V or 690 V it holds 17 kA. That means this breaker can be the main disconnect on a 415 V switchboard with a transformer-fed fault current up to 121 kA — no need to cascade a current-limiting fuse upstream. The TM240 thermal-magnetic release handles overloads and short-circuits in one package; no electronic trip unit to program or battery to maintain.
Thermal derating — it holds 20 A through 55 °C
The 20 A rating is flat from 40 °C to 55 °C. At 60 °C it derates to 19 A, and at 70 °C it's still 19 A. That gives you headroom in a hot panel — no need to oversize the breaker for a 50 °C ambient. Maximum operating temperature is 70 °C, storage from -40 °C to 80 °C. Power loss is 12 W at full load, which matters for heat buildup in a sealed enclosure.
Panel fit — dimensions and mounting
Breaker measures 130 mm high, 76.2 mm wide, and 70 mm deep. It clips onto the DIN rail or mounts via rear screw terminals.
Auxiliary switches and options
Comes with two auxiliary switches HQ (high-qualified) built in — no separate order for a signal contact. No undervoltage release, no ground-fault monitoring, no communication function, no voltage trigger, and no trip indicator. It's a bare line-protection breaker with the aux contacts as the only add-on. If you need shunt trip or UVR, that's a different order code in the 3VA family.