How to Read a Residential Wiring Diagram

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Residential electrical diagrams vary according to what the diagram is for and who is compiling the information. These kinds of diagrams are helpful in aiding homeowners in not only wiring their own home but locating the existing wires within the completed structure. Diagrams that are in color, not just black and white, may be more helpful the novice reader however everyone should be aware that the symbols used on their diagram may be different from others for currently there is no "official code" regarding the use of symbols on blueprints or schematics for residential drawings.

Things You'll Need

  • Symbol key
  • Reference book or chart
  • Dictionary
  • Wiring diagram
  • Obtain a key or reference chart for use when identifying the wiring symbols. Most wiring diagrams will have one included on the printout. If one is not included, libraries usually have a good selection of reference material regarding electrical symbols. Some dictionaries, such as Webster's, have the symbols included in the back.

  • Acquire a copy of the wiring diagram for your home. If it is being built, or is a newer home, try getting one from the contractor or architect. For older homes, the local code enforcement office may have a copy in larger municipalities however for some projects the diagram may not be available except through the previous homeowner or builder.

  • Locate the main panel on the diagram. This panel is where the main power line enters the residence and is typically indicated by a diagonally striped or shaded rectangle shape located on/in a wall in a utility room, garage or basement. On some drawings, there may be an angled line extending from the panel icon as to indicate an open door.

  • Recognize the switches. Switch symbols usually resemble an "S," with or without a single or multiple lines running vertically through it; however it may have a small number beside it in lieu of the lines. The number, or number of lines, usually indicates the type of switch that will be installed along with how many.

  • Identify the outlets. Outlets usually are small, unshaded circles, with one line leading from the circle to the wall. If there are two lines, it indicates multiple outlets. Three lines mean an appliance outlet for larger items like dryer and ranges. A letter "S" beside the outlet means it is "switched" and can be turned off and on with a switch. If there is a number next to the circle, it means there will be more than one outlet installed. Special purpose outlets will have a triangle inside the circle. And floor outlets are indicated by a dot inside a circle.

  • Find the fixtures. Fixtures are things such as lights, fans, exhaust vents over stoves, etc. Lights are usually drawn as a circle with four lines extending out from the sides. Recessed lights may have a square shape around them. Vanity, track, and bar lights may be a series of small circles attached to a rectangle. Spotlights may be two side-by-side triangles. Fluorescent lights are usually a long rectangle shape.

  • Identify the special symbols. Special symbols indicate things such as thermostats (a circle with a "T"), smoke detectors (a circle with an "SD"), phones (a lone triangle with line to wall), doorbells (a square with a circle within), and televisions (a rectangle with the letter "TV"). Ceiling fans look like small, four-bladed fans. And electrified exhaust vents or vents are usually square with an "X" shape inside.

Tips & Warnings

  • Follow the dotted lines to find switches more easily on drawings.
  • Always refer to the key on the diagram.
  • If not sure, ask a professional.
  • Diagrams are usually used as guides; check on-site for actual placement.
  • Never work on a live circuit.

References

  • Blueprint Reading and Sketching for Carpenters--Residential; McDonnell; Van Nostrand Reinhold Co.; 1981; ISBN 9780442262655
  • Residential Construction Academy House Wiring; Fletcher; Cengage Learning; 2003; ISBN 9781401813710
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