To provide a method of installing a new bus duct for connecting between a generator bus in a main switchboard and a new feeder panel when the new feeder panel is additionally installed on the back side of the main switchboard or at a nearby place to perform power feeding, for power supply to ballast water treatment equipment, etc., in a ship on service.

When a new feeder panel is additionally installed on the back side of a main switchboard or at a nearby place and a new bus duct for connecting between a generator bus and the new feeder panel is installed so as to allow power supply from the generator bus in the main switchboard to ballast water treatment equipment, etc., the new bus duct is connected to a place for connecting the generator bus and a bus leading to a NO.2 generator. The new bus duct is raised from the generator bus onto a top surface of the main switchboard, laid therefrom to right above the new feeder panel, over the top surface of the main switchboard, let down toward the new feeder panel, and led into the new feeder panel.