What this MCCB is and what it protects
The Siemens SENTRON 3VA1120-3EF36-0AC0 is a 3-pole molded case circuit breaker (MCCB) rated 20 A continuous at 40 °C, designed for line protection in commercial and industrial distribution panels. It carries a TM240 thermal-magnetic trip unit — the thermal element handles overloads, the magnetic element clears short circuits — and breaks up to 75.6 kA at 240 V, 52.5 kA at 415 V, and 32 kA at 440 V. That interrupting capacity means it can safely clear a fault all the way up to those levels without welding contacts or venting gas into the enclosure; you don't need an upstream current-limiting fuse to protect the breaker itself. The 70 mm depth and 76.2 mm width let it drop into standard SENTRON panel footprints alongside other 3VA frame breakers.
Thermal derating and real-world current
Rated 20 A from 40 °C through 55 °C, then derates to 19 A at 60 °C through 70 °C. That's a shallow derate curve — you lose only 1 A over a 30 °C rise — so in a warm panel next to a drive or transformer the breaker holds its rating. Ambient operating range is -25 °C to 70 °C, storage from -40 °C to 80 °C. The 12 W maximum power loss matters for panel thermal budgeting if you're stacking several breakers in a closed cabinet.
What fits and what doesn't
Mounts in the standard SENTRON 3VA panel cutout — 76.2 mm wide per pole, 130 mm tall. No undervoltage release, no shunt trip, no communication module on this variant; it's a straight thermal-magnetic breaker with two HQ auxiliary contacts for status feedback. The insulation voltage is rated 800 V, so it's comfortable on 480/277 V and 600 V systems. If your panel was laid out for a 3VA1110 frame, check the depth — this one is 70 mm, which matches the 3VA1110 depth, so it should drop in without rewiring as long as the bus bars and lug kit align.