The power distribution system of the construction site is classified into three levels, and the main distribution board (or distribution room) is set. The main distribution board. The distribution box has the characteristics of small size, simple installation, special technical performance, fixed location, unique configuration function, not limited by the site, relatively common application, stable and reliable operation, high space utilization, less land occupation and. The power distribution system at the construction site shall be distributed in different levels. The back of an antique electrical room, still operational at a US plant as of 2014. All conducting busbars are open and operators must be careful not to touch them.