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How Do I Read Electrical Diagrams?

Residential electric meter.
A residential power outlet.
When troubleshooting for electrical problems, first read the home's schematic drawings to see how it's wired.
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  • Written By: Carol Francois
  • Edited By: Heather Bailey
  • Last Modified Date: 21 September 2014
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Electrical diagrams are schematic drawings used to describe electric circuitry. These drawings are created for any product that uses electricity, ranging from an electrical device to an entire building. The terms and symbols used are consistent, regardless of the application. Electrical diagrams are typically created by electrical engineers for products and architects for buildings.

You must remember three things about all electrical circuits when reading electrical diagrams. The first item is that all circuits must move electricity from one place to another. In practical terms, every circuit has a clear beginning, end and purpose.

The second item is the control element. There must be a method of controlling the amount of electrical force in the circuit. The third item is that every circuit must start and end at a voltage source. These sources do not have to be the same, but there must be a complete loop.

Electrical diagrams use internationally accepted standard symbols to represent various items. Most electrical drawings include a legend or key, providing an explanation of each symbol. These symbols are consistent around the world and provide a quick method to identify the way a circuit is working and to troubleshoot any potential problems.

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For example, the image of a line with a coil around it is a relay or automatic switch. The legend will provide the exact image with a letter code, such as "C" for coil. Every coil image will have the same symbol, but will be uniquely numbered in sequence. Inside the image is a circle, which is used to record a letter that corresponds to a set of contacts that are operated by that coil. The amount of electricity in the circuit is written in volts along the circuit line.

If there are any limitations on the voltage of a circuit or electrical outlet, this value is written on the actual item. A switch or control element is shown by breaking the straight circuit line at a 20 degree angle. A space is shown to indicate the break, the line restarts on the opposite side and continues to the source.

When reading an electrical diagram, start at the main power source. Follow a circuit with your finger to see where it goes and what it does. Repeat this process with all the circuits. This method takes time, but provides valuable insight into the operations of the circuit, how it is connected, and the basic design of the product.

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hamje32
Post 3

@David09 - That’s definitely good advice. Nowadays you can also use electric diagram software that works like a CAD program. You design your own circuits, and can swap components in and out with different amperage values. The software creates a “virtual” circuit and you can see the results of your modifications without blowing anything up.

It’s the next best thing to actual circuit construction and it’s a lot easier than messing with breadboards, plugging in components and so forth. Then when you’re done, you can take your virtual circuit and build a real-world version of it, knowing in advance that it will work.

David09
Post 2

The best way to read and understand electric circuit diagrams is to read in conjunction with actual circuit construction. When I was a teenager I bought electronics kits from a local hobby store and built hundreds of small electronic projects. In the process I understood components and a little bit about circuitry.

I did so well that the army tried to recruit me in my later years, when I took vocational tests in high school and I basically aced the electronics portion of the tests. I’m not saying you have to do that, but a hands-on approach is definitely the best way to understand schematic diagrams.

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