What this MCCB is and what it does
The Siemens SENTRON 3VA1120-5EF36-0AD0 is a 3-pole molded case circuit breaker (MCCB) rated for line-protection duty. It carries a TM240 thermal-magnetic release — the thermal element handles overloads, the magnetic element handles short-circuits — set for a 20 A continuous rating at 40 °C. The insulation voltage is rated at 800 V, so it can sit in 480/277 V or 600 V panels without creeping issues.
Breaking capacity — the number that decides selectivity
This MCCB delivers 187 kA at 240 V AC, 121 kA at 415 V, 75.6 kA at 440 V, and 17 kA at both 500 V and 690 V. That 187 kA figure at 240 V is high enough for most transformer-secondaries and large-capacitor-bank feeds — it gives you headroom for selective coordination with downstream breakers without cascading upstream. At 690 V the 17 kA rating still covers standard industrial motor circuits.
Thermal derating — don't assume 20 A at every panel temperature
The 20 A rating holds from 40 °C up to 55 °C. At 60 °C it derates to 19 A, and it stays at 19 A through 70 °C. If your panel ambient runs above 55 °C — say a sealed enclosure next to a furnace line — you lose 1 A. That matters for a continuous load near the breaker's nameplate. The power loss at rated current is 12 W, so thermal management inside the enclosure is manageable.
Physical fit and panel integration
The breaker measures 130 mm high, 76.2 mm wide, and 70 mm deep. That 76.2 mm width (3 inches) is the standard 3-pole MCCB footprint — it occupies three 25 mm DIN-rail module positions. The depth of 70 mm (2.76 in) leaves room for rear-mounted busbars or a panel gland plate without forcing an oversized enclosure. Operating temperature range is -25 °C to 70 °C; storage range is -40 °C to 80 °C.