Line protection MCCB with TM240 release
The Siemens SENTRON 3VA1120-3EF32-0KC0 is a 3-pole molded case circuit breaker rated for 20 A continuous current (Iu) with a TM240 thermal-magnetic overcurrent release. It's configured for line protection duty — meaning it protects cables and busbars from overload and short-circuit, not motor or generator circuits. The 75.6 kA breaking capacity at 240 V gives you headroom for high-fault installations; at 415 V it still interrupts 52.5 kA, and at 690 V it holds 10.5 kA. That spread tells me this breaker is sized for a 480 V or 600 V class panel where the available fault current is known and substantial. The TM240 release is a thermal-magnetic design — the thermal element handles overloads on a time-current curve, the magnetic element trips instantaneously on short-circuit. No electronic adjustment, no communication module, no ground-fault monitoring. That keeps the part simple and field-reliable when you just need a fixed-trip breaker for a feeder or branch circuit. The auxiliary contact version ships with two HQ auxiliary switches (form C) for status feedback to a PLC or annunciator panel.
Thermal derating and ambient limits
The 20 A rating holds at 40 °C, 45 °C, and 50 °C ambient — no derating needed in a typical ventilated enclosure. At 55 °C it drops to 19.2 A, at 60 °C to 18.8 A, at 65 °C to 18.4 A, and at 70 °C to 18 A. If your panel runs hot near the top of a crowded cabinet, that 18 A floor at 70 °C is the number to size against. The operating ambient range is -25 °C to 70 °C; storage range is -40 °C to 80 °C. The IP40 front protection means it's suitable for a clean indoor panel — not washdown or outdoor without an enclosure.
Auxiliary and shunt trip integration
This breaker includes a shunt trip (STL) release for remote tripping — energize the shunt coil and the breaker opens, useful for emergency-stop circuits or remote load shedding. The auxiliary contact version provides two HQ switches for status indication. The integrated auxiliary trip module carries order code 3VA9688-0BL33; if you're replacing that sub-assembly, that's the part number. No undervoltage release, no phase-failure detection, no ground-fault monitoring — this is a straightforward line-protection breaker with remote trip capability.