When reading a diagram, first determine the voltage of the circuit. Next, study all the symbols and color coding of the diagrams. After you've studied all the elements, examine the diagram from left to right and from top to bottom, and find the information you need.
To determine the voltage of a circuit, find the main lines on the diagram and the letters that represent them. A 110V circuit has lines L1 and N in the wiring diagram. A 110-240V circuit has lines L1, L2 and N in the diagram. A 240V circuit has lines L1 and L2 in the diagram.
The symbols usually look like the objects they represent. For example, an oval with a wavy line inside of it usually represents a light. An opening or a break in a line usually represents a switch.
Colors on a wiring diagram also have meanings. Information about what each color represents is usually indicated on each diagram. However, colors on diagrams of home electrical systems usually have the same meaning. Hot wires that transport the power to the object are usually indicated as black, red or blue. Neutral wires that transport power to the service panel are usually white. Ground wires transport power to the service panel if neutral wires break, and they are green.