What this MCCB is and what the ratings mean for fit
The Siemens 3VA1120-5MH32-0AA0 is a SENTRON molded case circuit breaker (MCCB) designed specifically for starter protection — meaning it is built to protect motor starters and their associated control circuits, not just general distribution feeders. Three poles, rated 20 A continuous at 40 °C through 55 °C, and derated to 19 A at 60 °C through 70 °C. That flat thermal curve from 40 °C to 55 °C is unusual and useful: you get full 20 A rating across the typical panel ambient range without having to oversize the frame. The headline number here is the breaking capacity: 187 kA at 240 V, 121 kA at 415 V, 75.6 kA at 440 V, and 7.5 kA at 500 V and 690 V. That 187 kA at 240 V tells you this breaker is sized for high-fault locations — large transformer secondaries or industrial switchboards where the available fault current is well above what a standard 65 kA or 100 kA MCCB can handle. At 415 V the 121 kA still covers most heavy industrial installations. The drop to 7.5 kA at 500 V and 690 V is the limit for higher-voltage motor circuits; if your system runs at 690 V, verify the available fault current stays under that threshold. The overcurrent release is a TM120M — thermal-magnetic, fixed-trip type. The '120M' designation means the magnetic short-circuit pickup is fixed at 120 A (6× the 20 A rating). That fixed magnetic setting is typical for starter protection: it allows motor inrush without nuisance tripping but still clears a bolted fault fast. No undervoltage release, no ground-fault monitoring, no communication module — this is a standalone thermal-magnetic MCCB for straightforward motor branch circuits.
Panel fit and mounting
Dimensions: 130 mm height, 76.2 mm width (3 inches), 70 mm depth. That 3-inch width is the standard 3-pole MCCB footprint for the 3VA frame size — it occupies one 3-inch slot in a panel or switchboard. The 70 mm depth is shallow enough to fit in most distribution enclosures without interfering with the door or deadfront. IP40 on the front means the breaker face is protected against tools and small wires, but the body is not sealed against moisture — keep it in a dry indoor enclosure. Power loss is 12 W maximum at rated current. That is moderate for a 20 A MCCB; factor it into the enclosure thermal budget if you are packing multiple breakers in a small panel. The insulation voltage is rated 800 V, so the breaker can be used in 690 V systems without derating the internal clearances.