What it is and what it does
The Siemens SENTRON 3VA1120-4EF36-0AC0 is a 3-pole molded case circuit breaker (MCCB) rated for line protection, carrying a continuous current of 20 A at 40 °C ambient — derated to 19 A at 65 °C and above. Its TM240 thermal-magnetic overcurrent release provides fixed thermal and magnetic trip settings, so the breaker is sized for a specific load and not field-adjustable. The 121 kA interrupting rating at 240 V AC means it can safely clear a fault up to that level without upstream coordination failure; at 415 V the rating drops to 75.6 kA, and at 690 V to 11.9 kA, which governs where it can be placed in the distribution hierarchy.
Panel fit and integration
The breaker occupies 76.2 mm width on the DIN rail, with a 70 mm depth and 130 mm height — standard for the SENTRON 3VA frame size. The 2 auxiliary switches (HQ type) mount internally and share the breaker's compact envelope, so no external auxiliary block adds panel depth. Rated insulation voltage is 800 V, which covers 480 V and 600 V class systems with margin. Maximum power loss at rated current is 12 W, a figure to consider for enclosure thermal budgeting when grouping several breakers.