This Electrical Ladder Diagram is an electrical notation and symbology commonly used to show how electromechanical switches and relays are linked. The two vertical lines are called rails; they connect to opposite poles of a power supply, typically 120 volts AC. For depicting equipment layout, and Electrical Ladder Diagram can be very accurate. All connection wires are shown and linked from one component to the next. Electricians use these diagrams frequently when connecting electrical or electronic equipment, and technicians use them when maintaining equipment. Horizontal lines shown in a ladder diagram are referred to as rungs, and each one represents a distinct parallel circuit branch between the power supply's poles.