What this MCCB is and where it fits
The Siemens 3VA1120-5EF36-0AB0 is a SENTRON molded case circuit breaker (MCCB) built for line protection in distribution panels. It carries a rated continuous current Iu of 20 A across three poles, with a TM240 thermal-magnetic overcurrent release — meaning the thermal element handles overloads and the magnetic element handles short-circuits, no electronic trip unit inside. The interrupting capacity hits 187 kA at 240 V and still holds 121 kA at 415 V, so it's sized for high-fault installations like transformer secondaries or large motor control centers where available fault current is substantial. The front face is rated IP40, which keeps tools and fingers out but isn't sealed against hose-down — this is a dry indoor panel part.
Ratings and what they mean for your panel
The 20 A rating holds flat from 40 °C to 50 °C — no derating needed in a warm enclosure. Above that it drops gradually: 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 ambient runs 55 °C, you're still good for a 19 A continuous load without nuisance tripping. The 800 V rated insulation voltage (Ui) tells you the breaker can be used in 480 V or 600 V systems with comfortable margin. The interrupting curve at 690 V drops to 17 kA, so if you're on a 690 V IT system, verify the available fault current is below that. Dimensions are 70 mm deep by 76.2 mm wide by 130 mm high. The 76.2 mm width is three standard 25.4 mm pole pitches — it will bolt directly onto a DIN rail or panel-mount foot without adapters. Two auxiliary switches (HP type) are built in for status feedback to a PLC or indicator lamp; no separate aux block to order and snap on.