Main circuit breaker calculation is a step-by-step process that involves identifying total load, converting to current, applying demand factors, adding safety margins, and matching conductor size. Correct sizing prevents electrical hazards, ensures system reliability, and. Calculating the correct size of a main circuit breaker is one of the most important steps in electrical design. An undersized breaker trips frequently, while an oversized breaker poses serious fire risks. It is typically open-type, allowing easy replacement of contacts and parts, and can be equipped with various accessories. ACBs are commonly used as main power supply switches.