How to read electrical symbols in schematics

Written by carlos mano
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How to read electrical symbols in schematics
Electrical schematics show what connects to what. (Hemera Technologies/Photos.com/Getty Images)

Electrical schematics are often called wiring diagrams -- they show how all the electrical components are connected by wires. They are like maps that show how electricity flows through the system, but they are more like subway maps than road maps. Electrical schematics do not faithfully reproduce the distance between components, but they do faithfully reproduce what is connected to what. The components are all symbolic, and a large part of learning to read schematics is learning which electrical components are represented by each symbol.

Skill level:
Moderate

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Instructions

  1. 1

    Learn the power sources first -- these are where the electricity starts. There are basically two power sources: alternating current (AC) and direct current (DC). AC comes out of the wall plug and the symbol is a half circuit with two parallel lines running through it. DC comes from batteries, which are symbolised by a series of parallel lines that are alternately longer and shorter. A related symbol is the ground symbol. It is a wire that terminates in a series of approximately five parallel lines that get increasingly shorter.

  2. 2

    Control the flow of electricity with switches and learn to recognise switches in electrical schematics. A switch is represented by a break in a wire with a short line nearby that looks like it could be pushed into the gap to close it. There are many variations on this idea. Switches that switch between two circuits tend to have one end of the short line attached and the wires to the two circuits within reach if the short line is rotated. Push-button switches tend to be short parallel lines that can be pushed into place instead of rotated. Switches are shown in their "normal" position -- which can either open or close the circuit -- and the short line is moved when the switch is activated.

  3. 3

    Memorise the symbols you need to read the schematics you will be using. Schematics for house wiring will look different from schematics for computer circuits, which will be different from audio and television circuits. Typical symbols are the zigzag symbol for resistors, the short series of loops for coils, solenoids and relays, and two short parallel lines with a gap between them to symbolise a capacitor.

Tips and warnings

  • House wiring symbols tend to be simple squares or circles with a legend describing them. Integrated circuits tend to be rectangles that contain the appropriate part number.
  • Except for house wiring, the arrangement of components on a schematic does not usually correspond to the arrangement of components in the device the schematic represents.

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