The Schematic Diagram Resembles A Ladder In That It Is Made Up Of Two Vertical Lines. These diagrams documented how connections between devices were made on relay panels. The two vertical lines wires that serve as a boundary for the control system and deliver the control voltage to the devices are called the rails.
Ladder diagram are electrical diagrams that represents an electrical circuits in industries to document control logic systems. The left vertical line represents power rail voltage source while the right vertical line represents the ground or neutral. The rungs of the ladder between these two verticals.
The rails are the two dark vertical lines that represent the power source to the control circuit.
The ladder diagram shown in figure 4 is easy to read since there are only two basic parts the rails and the rungs. Writing a program is then equivalent to drawing a switching circuit. A very commonly used method of programming plcs is based on the use of ladder diagrams. The control circuit voltage is usually rated at 12v 120v depending on the rated values of the loads connected in the circuit.
