How to read wiring schematics

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How to read wiring schematics
Symbols depict the value of these resistors. (electronics 4 image by chrisharvey from Fotolia.com)

Wiring schematics illustrate the layout and value of a circuit. They are essential for understanding the scale and nature of closed circuits, such as those found inside radios, lighting systems and electric gates. Every electrical system has a wiring diagram, but not all diagrams are available for public viewing. This is because some wiring diagrams are proprietary and have commercial value that would diminish if the owner shared them. Wiring schematics commonly accompany DIY electrical projects such as amplifier kits. Understanding wiring diagrams is essential if you plan to repair or assemble an electrical device.

Skill level:
Easy

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Things you need

  • Electrical symbol reference
  • Wire colour coding reference

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Instructions

  1. 1

    Learn the symbols. Rather than drawing each individual component, wiring diagrams typically incorporate a universal system of symbols. These symbols indicate components, their values and their relationships with each other. This system allows people who don't speak the same language to read the same wiring diagrams. The symbols are essential to understanding the circuit. The 'Learn C' website has a large list of symbol references. For example, a large black circle over two separate wires indicates that the wires are connected. This distinguishes them from wires that are joined but not connected. Essential components such as resistors and capacitors are depicted by symbols, and their value is typically denoted by an ohms symbol. Volts are indicated by the letter V. A straight line between two component symbols denotes that they are connected.

    How to read wiring schematics
    Knowing the value of the components is essential when working with circuits. (comparison of the information image by Yuriy Poznukhov from Fotolia.com)
  2. 2

    Make a note of the values. The value of a symbol is important because it helps you determine whether a circuit is working correctly. For example, if you are using a multimeter to test a transistor, you need to know the correct current for that transistor to compare with the meter reading. Note down the important values when studying a schematic, so that you have a handy reference when performing tests.

  3. 3

    Trace each wire back to its source. Use the schematic as a reference and physically follow each wire back to its source in the circuit. This will help you understand the physical layout of the circuit. Understanding the schematic in isolation is of no use if you don't know how that corresponds to the physical circuit.

  4. 4

    Learn the role of each type of wire. Most schematics are printed in black and white, but wires come in many colours. Typically the earth wire is green and yellow. In some older circuits it is just green, but this is rare. The neutral wire is blue and the hot wire is black. The International Electrotechnical Commission governs the colour coding system for electrical circuits.

  5. 5

    Keep a note of safety symbols. High voltages, ungrounded wires and any component that carries a live circuit will be highlighted on a schematic for safety. When you see these symbols ensure that you practice all safety procedures.

    How to read wiring schematics
    Schematics for circuits with potentially fatal voltages often feature this symbol. (warning sign for high voltage image by Roman Barelko from Fotolia.com)

Tips and warnings

  • Keep a symbol reference with you when you are reading wiring schematics. There's a lot of information to remember and even the most experienced electricians consult their references.
  • Never attempt to work with electricity if you are unsure what you are doing.

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