Improper selection of the circuit breaker in the small power distribution unit may cause a variety of faults. First, if the rated current of the circuit breaker is too small and cannot carry the load current in the circuit, it will cause the circuit breaker to trip overload and interrupt the circuit. In addition, if the rated current of the selected circuit breaker is too large and exceeds the circuit carrying capacity, it may cause the wires to overheat and even cause a fire. In addition, if the breaking characteristics of the circuit breaker do not match the needs of the circuit, for example if an inappropriate type is used, it may not be able to cut off the fault current in time, increasing the risk of damage to circuit components. Therefore, when selecting a circuit breaker, the load characteristics, rated current and characteristics of the circuit breaker must be fully considered to ensure that it can effectively protect the safe operation of the circuit.