The electrical engineer initiates one-line diagrams for new facilities and interprets one-line diagrams of existing facilities. This chapter illustrates some of the simple concepts involved in establishing a one-line diagram, determining system reliability, and determining breaker interrupting capacities. The total power requirement of a load is made up of two components, namely the resistive part and the reactive part. The problem facing the electrical engineer is to determine the power factor of the plant and to install equipment such as capacitor banks or synchronous motors so that the overall power factor will meet the utility company’s objectives. Transformer ratings are based on kilovolt-ampere. Since loads constantly change, a sizing based on the sum of the motor and miscellaneous loads, plus 25% extra gives a reasonable initial basis for determining capacity. The loads of many institutions and industry are usually more inductive loads that include motors and transformers.