MCCB for line protection — 20 A, 3-pole, TM240 release
The Siemens SENTRON 3VA1120-3EF36-0AF0 is a 3-pole molded case circuit breaker (MCCB) rated at 20 A continuous at 40 °C, designed specifically for line protection — meaning it guards cables and busbars against overload and short-circuit, not motor or generator circuits. The TM240 thermal-magnetic release provides fixed thermal and magnetic trip thresholds, so it's a set-and-forget device: no field-adjustable pickup to mis-calibrate. Breaking capacity runs 75.6 kA at 240 V, stepping down to 52.5 kA at 415 V and 32 kA at 440 V, which covers most industrial service-entrance and distribution panel fault levels. Rated insulation voltage is 800 V, giving headroom for 480/277 V or 600 V systems.
Breaking capacity and selectivity — what the ratings mean for your panel
At 240 V the 75.6 kA interrupting rating is high enough for most main-breaker positions in North American distribution. At 415 V (common in IEC markets) the 52.5 kA still handles substantial fault current — enough to coordinate with upstream transformers in the 1–2 MVA range. The drop to 32 kA at 440 V and 11.9 kA at 500/690 V reflects the physics of arc extinction in air at higher voltages; if your system runs 690 V, verify the available fault current is under 11.9 kA or step to a higher-rated frame. The TM240 release holds 20 A through 55 °C, then derates to 19 A at 60–70 °C — useful when the breaker is in a warm enclosure near other heat sources.
Panel integration — footprint and aux switching
The 3VA1120-3EF36-0AF0 measures 130 mm high, 76.2 mm wide, and 70 mm deep — a standard 3-pole MCCB footprint that fits Siemens SENTRON distribution panels and most DIN-rail-mount enclosures with the appropriate adapter. The integrated 1 auxiliary + 1 trip alarm switch HQ provides remote status indication (breaker open/closed and tripped) without needing an add-on module. Power loss is 12 W maximum at rated load, so factor that into enclosure thermal calculations if the panel is densely populated.