What it is and what it does
The Siemens SENTRON 3VA1120-4EF32-0KH0 is a 3-pole molded case circuit breaker (MCCB) rated for 20 A continuous current (Iu) and fitted with a TM240 thermal-magnetic release. It is a line-protection device — meaning it protects cables and busbars from overload and short-circuit, not a motor-protection breaker with adjustable trip curves. The 121 kA interrupting rating at 240 V AC gives it the headroom to sit upstream of smaller breakers in a high-fault panel without needing a current-limiting fuse ahead of it. At 415 V it still breaks 75.6 kA, and at 690 V it holds 11.9 kA — so it stays selective across common industrial voltage levels.
Thermal derating and real-world current
The 20 A rating holds flat from 40 °C to 50 °C. Above that it derates: 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 the panel ambient runs hot — say, a sealed enclosure next to a drive — the actual continuous current you can pull is closer to 18 A. That is the number to use for conductor sizing and load planning, not the 20 A nameplate.
Auxiliary and trip options
This version ships with 2 auxiliary switches plus 1 trip alarm switch (HQ type) and a shunt trip (STL) release for remote tripping. The shunt trip is field-wired to a control voltage — common for emergency-stop or PLC-driven shutdown circuits. There is no undervoltage release, no ground-fault monitoring, and no communication module on this variant. The integrated auxiliary trip order code is 3VA9688-0BL33, which is the factory-fit accessory that comes pre-installed.
Mounting and panel fit
The 3VA1120-4EF32-0KH0 mounts on a DIN rail or can be screw-fixed to a backplate. Dimensions are 76.2 mm wide, 130 mm tall, 70 mm deep — that is a standard 3-pole MCCB footprint for the SENTRON 3VA platform. The front face carries an IP40 rating, so it is fine for a clean indoor panel but not for washdown zones. The 15,000-cycle mechanical endurance is typical for this class — enough for a distribution feeder that operates a few times a year, not a daily-switched load.