Each switch box shall connect to and control only one associated piece of electrical equipment (including sockets). The following is a detailed introduction about it: - **First-level Distribution. As for the equipment inside, there are certain differences: the first level distribution cabinet generally has isolation switches, circuit breakers, leakage protectors, etc., the second level contains a large three-phase circuit breaker, and the third level contains a single-phase circuit breaker. As well as purely technical factors (intensity, number of outputs, etc. ), the choice of a distribution system is critical regarding implementation, maintenance, operating requirements and poss bility of evolving the panels.