Both air circuit breaker (ACB) and molded case circuit breaker (MCCB) are used for the safe switching on and off of electrical systems. In principle, both serve the same purpose. The ACB is usually found on the upstream side of the circuit, while the MCCB is found on the load-side control (usually, the load-side switch operates more frequently than the upstream). These three protection devices are selected according to the required operating voltage and protection level (fault level) of the system. As technology continues to advance, the ratings and breaking capacities of MCCBs are increasing, so the applications of ACBs and MCCBs may overlap.