How to read circuit wiring diagrams

Written by kim lewis
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How to read circuit wiring diagrams
A wall outlet (electric outlet image by Dawn Williams from

Circuit wiring diagrams are important tools in electronics. They are representations of circuits, and so allow users to replicate them without needing models or having to be physically present. Their form makes it an easy way to transmit important information.

Circuit wiring diagrams are different from schematics in that they emphasise pictures instead of symbols. They show the positions of the wires, and how the devices are physically arranged next to each other. They are useful in troubleshooting circuits that don't work properly. To learn to read circuit wiring diagrams, it is necessary to learn some basic rules.

Skill level:
Moderately Challenging

Things you need

  • Switch or outlet circuit wiring diagram
  • Basic home repair text

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  1. 1

    Memorise the colours most often used to distinguish the role of wires in circuits. The hot wires are normally coloured red and black. Red is connected to the positive side of a voltage source, while black is connected to the negative side. Green or bare wire usually means neutral, which means it is connected to a point on a device that carries no current. There may be additional wires as well, and some diagrams may use colours different from the ones stated. These will be clearly indicated.

  2. 2

    Study the different types of switches, including their purpose and operation. Switches are one of the most common types of devices shown in wiring diagrams. Popular ones include light dimmers, and three-way or four-way switches. Three-way switches let the user control electricity from two areas, such as controlling one lamp from two different floors. Four-way switches can control electricity from three areas.

  3. 3

    Examine the different types of outlets, which are another very popular subject for wiring diagrams. Outlets for household use are usually made for 110 to 120 volts, and have ground connections. Dryers and other large household appliances may require 240-volt outlets.

  4. 4

    Recognise the symbols and drawings used most often in circuit wiring diagrams. Coloured lines are used to represent wires and their various roles. Lamps are symbolised using light bulbs. Outlets and switches have drawings that clearly look like them, though some may be shown as merely boxes or rectangles.

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