Ladder diagrams are used to depict electronic control circuits in a simple form. These schematic diagrams resemble a ladder with rails and rungs. Special symbols are used to show the different components depicted on the diagram.
Ladder diagrams usually display two different types of components: the power component and the control component.
A power component on the diagram might be a motor. Other power components are protective devices such as fused relays or circuit breakers.
The control rungs of the ladder show all the input and output devices that make the power components do their work. Control components include input devices which can either allow current flow or disrupt current flow and output devices.
Input devices include switches of various types. They control the current flow to output devices such as LED lights.
By simplifying the way circuit elements are depicted, ladder diagrams make it possible for technicians all over the world to understand exactly what a circuit schematic is showing. Standard symbols on ladder diagrams make the technician's work much easier.