What this MCCB is and what it does
The Siemens SENTRON 3VA1120-4EF32-0BA0 is a 3-pole molded case circuit breaker (MCCB) rated for 20 A continuous current, with a TM240 thermal-magnetic overcurrent release. It's built for line protection — meaning it sits on the feeder side of a panel, protecting downstream wiring and loads from overloads and short circuits. The 121 kA breaking capacity at 240 V tells you it can safely interrupt a fault up to that level without welding contacts or cascading upstream; at 415 V that figure is 75.6 kA, at 440 V it's 52.5 kA, and at 690 V it's 11.9 kA. That's a high-interrupting rating for a 20 A frame — it's sized for high-fault environments like industrial switchboards or transformer secondaries where available fault current is substantial.
Thermal derating and ambient temperature
This breaker holds its full 20 A rating up to 50 °C ambient. Above that it starts to step down: 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 your panel runs hot — say near a drive cabinet or in a non-conditioned enclosure — that derating curve is what you size against, not the nameplate 20 A. The operating range is -25 °C to 70 °C, storage from -40 °C to 80 °C.
Built-in undervoltage release, no auxiliary contacts
This version ships with an undervoltage release (UVR) — it will trip the breaker if the control voltage drops below a set threshold, which is common for emergency-stop or undervoltage protection schemes. There is no auxiliary contact block included (order separately if you need status feedback), no ground-fault monitoring, no phase-failure detection, and no communication module. The integrated auxiliary trip is order code 3VA9608-0BB11 if you need a shunt trip. The TM240 release is thermal-magnetic, fixed, non-adjustable — set at the factory for 20 A.
Panel fit and dimensions
The breaker measures 76.2 mm wide (that's 3 inches — standard for a 3-pole MCCB in this frame), 130 mm tall, and 70 mm deep. It mounts on a DIN rail or can be screw-fixed to a backplate. The IP40 front protection means it's splash-proof from the front but not sealed; keep it inside a panel enclosure. No trip indicator on the front — you'll need a voltmeter or a downstream indication to confirm state.