A conceptual layout of a ship’s distribution system that adopts a ‘radial’ or ‘branching’ methodology is depicted in picture. Note that the shore supply circuit is connected to the emergency switchboard but this is only for the convenience of cable-laying. Often the shore-supply circuit is controlled from the main switchboard.
The circuit breakers and switches are the means of controlling the flow of electric current. Fuses and relays (not shown in the diagram) protect the distribution system from the damaging effects of large fault currents. The electrical load is divided into ‘essential’ and ‘non-essential’ services.
Essential services are those required for safety of personnel and for the safe navigation and propulsion of the ship. They include certain supplies to navigational aids, machinery spaces, control stations and steering gear.
The essential services may be supplied directly from the main switchboard or via section or distribution boards; however most essential services are fed via the emergency switchboard.