What this MCCB is and what it does
The Siemens SENTRON 3VA1120-4EF36-0KH0 is a 3-pole molded case circuit breaker (MCCB) rated 20 A at 40 °C, designed for line protection in distribution panels. It carries a 121 kA breaking capacity at 240 VAC — that means it can safely interrupt a fault current up to 121 kA without welding contacts or cascading failure upstream. At 415 VAC the interrupting rating is 75.6 kA, and at 690 VAC it still holds 11.9 kA, so it handles high-fault commercial and industrial service entrances where the available short-circuit current is substantial.
Ratings that drive the panel design
Rated insulation voltage is 800 V, which sets the dielectric withstand for the internal bus and isolation coordination. The breaker is rated 20 A continuously at ambient temperatures up to 55 °C; at 60 °C it derates to 19 A, and holds 19 A through 70 °C. That thermal curve matters when the MCCB is packed into a crowded enclosure — you can load it to 20 A in a 55 °C panel, but above that you lose 1 A. The 3VA1120-4EF36-0KH0 includes a shunt trip (STL) for remote tripping and a configurable auxiliary switch block with 2 auxiliary switches plus 1 trip alarm switch (HQ), so it can signal status back to a PLC or BMS without a separate interface relay.
Panel integration and footprint
The breaker measures 130 mm high, 76.2 mm wide, and 70 mm deep — a 3-pole MCCB that fits standard 3-inch-wide panel mounting. The depth of 70 mm (2.76 in) leaves clearance for rear-mounted bus bars or cable ducts. Operating temperature range is -25 °C to 70 °C; storage range is -40 °C to 80 °C. Maximum power loss is 12 W, so ventilation in a sealed enclosure is advisable if multiple breakers are ganged.