Single-line diagrams show the electrical circuitry down to, and often including, the major items of utilization equipment. They should show all electrical equipment in the power system and give all pertinent ratings. In making this type of diagram, it is basic that voltage, frequency, phase, and normal operating position be included. No less important, but perhaps less obvious, are items such as transformer impedance, available short-circuit current, and equipment continuous and interrupting ratings. Other items include current and potential transformers and their ratios, surge capacitors, and protective relays. If one diagram cannot cover all the equipment involved, additional diagrams, appropriately noted on the main diagram, can be drawn.
Schematic diagrams should be arranged for simplicity and ease of understanding circuits without regard for the actual physical location of any components. The schematic should always be drawn with switches and contacts shown in a de-energized position.
Wiring diagrams, like schematics, show all components in the circuit but arranged in their actual physical location. Electromechanical components and strictly mechanical components interacting with electrical components should be shown. Of particular value is the designation of terminals and terminal strips with their appropriate numbers, letters, or colors. Wiring diagrams should identify all equipment parts and devices by standard methods, symbols, and markings.
Layout diagrams, plot plans, equipment location plans, or facility maps should show the physical layout (and in some cases, the elevations) of all equipment in place.