A single, or one-line diagram of a distribution system is a simple and easy-to-read diagram showing power supplies, loads, and major components in the distribution system (Figure 1).

Commercial or Utility Power

Commercial or utility power is electrical power that is provided by commercial generating systems to the facility.

Diesel Power

Diesel power is power generated by a diesel-driven generator. Diesel-driven generators are the most economical and practical source of "standby power."

Figure 1 One-Line Distribution Diagram

Failure-Free Power

Failure free power is accomplished by providing vital equipment with automatic switching between two or more power supplies so that interruption of power is minimized.