When an architect designs a new project, he works with engineers and consultants to create a complete set of blueprints. One section of these drawings, the electrical blueprints, shows how the electrical system of the building is to be constructed. These plans show receptacles, light switches, wires, light fixtures and any other items that need to be powered by electricity. The lines and symbols shown on these drawings can often seem like a foreign language, but it is actually fairly easy to read electrical blueprints. All of the keys to interpreting the plans are shown within the drawings, and as soon as you know where to find them, you'll understand what the prints are saying.
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Start with the architectural floor plans. Architectural plans often have room names and additional information about the project that is not shown on the electrical plans. By reviewing these plans first, you can get an idea of the layout and intent of the space, which will help you understand the electrical drawings.
Review the symbol legend. Electrical components are represented by various symbols, and the symbol legend tells what each one means. You can find the legend on the title page of the plans or on the first page of the electrical drawings.
Understand wiring diagrams. The electrical plans show the paths that wires will take from each piece of equipment back to the panel. The number shown by these wires indicates the breaker that each wire will be run on. This is helpful to understand because you can see which items are grouped together on a single breaker.
Consider phasing. Often, all of the lights in a room may be on one breaker, or all of the equipment in a certain section of the house may be grouped together. This is called phasing. When reviewing plans, pay careful attention to which items are phased together, and see if they are grouped appropriately.
Examine the lighting plan. This is often a separate document from the wiring drawings and shows the layout and type of light fixtures to be used. Review the symbols legend to understand what type of lighting is being used.
Read the specifications manual. Most sets of blueprints are accompanied by a manual, sometimes called a "spec book." Division 16 of the spec book gives electrical requirements and specifies materials to be used on the job. Often, notes and information are given in the spec book and not shown on the plans, so it's important to have both the book and the plans when reviewing the job.