When it comes time to modernize an electrical system or design an entirely new system, an up-to-date one-line diagram of the electrical system is an invaluable tool. It uses single lines and standard symbols to show electrical wire or busbar and component parts of an electric circuit or system of circuits.
The one-line diagram is entirely different from a wiring (or connection) diagram which shows exactly which wire is connected to what terminal. The one-line diagram shows the control strategy for system operation; how the system works. For example, a three-phase load uses three wires, each wire having its own pole of a control switch, and one overcurrent device. It is not necessary to repeat this information three times on the diagram; one line shows what happens to all three of the wires.
Preparing A One-Line Diagram
Example No. 1: Lighting Feeder & Branch Circuits
