1Single-line electrical diagrams are similar to Process Flow Diagrams (PFDs) used in industrial instrumentation, concentrating on the process flows more than the monitoring and control equipment. It is important to note that single-line diagrams are not the same as electrical schematics: in a single-line diagram, each line represents a set of power conductors (typically three or four conductors if the power system is 3-phase, which most large-scale AC power systems are). For this reason, we must interpret a single-line diagram much more like a pipeline system than an electrical circuit, in that the electrical power flows in one direction at any given time through these single lines, never making a complete loop as is the case in real life and in an electrical schematic diagram.