Follow Along on SkillCat: "Reading Electrical Drawings & Blueprints" Course!
In this guide, learn about the makeup of electrical drawings and plans, as well as how to read them.
Electrical Drawings
Electrical drawings or schematic diagrams give a visual representation of electrical systems and electrical wiring for electricians and electrical engineers to utilize. They include various electrical components, like electrical outlets, fixtures, switches, lighting, fans, and appliances. The details of an electrical supply from the power source to each electrical equipment in the building are provided on electrical plans.
The First Page
The first page of an electrical plan consists of general notes, along with legends and electrical symbols. General notes provide instructions followed during the complete installation of wiring, switches, lights, and appliances. It also includes details of the owner’s requirement or renovation guidelines.
Electrical systems like lights, switches, circuit breakers, distribution panels, and fixtures are denoted using various electrical symbols described in legends. Legends often contain abbreviations with electrical symbols used for appliances, switches, panels, and other fixtures shown in a plan. Floor plans, however do not include notes or details for all those electrical symbols used on the plan. Thus, it's recommended to look over the legends before moving on to the floor plans.
Electrical drawings contain many fixtures, switches, and panels. To avoid confusion, abbreviation tables are included to provide details of text written beside several electrical symbols for electrical components in a diagram. Since electrical plans are schematic, they use electrical symbols and abbreviations to denote the various appliances and electrical systems such as distribution panels, starters, sound system, television, and many more. Abbreviations used might differ from plan to plan. For example, if a plan consists of a symbol with text TV or MCC, the abbreviation table to find their full form may give you something like this:
TV - Television
MCC - Motor Control Center
Reading Electrical Drawings & Diagrams
In wiring diagrams like the one above, wall lines are often drawn lighter than the fixtures with dark lines to make the system particulars stand out clearly. In some instances, the fixtures might be shaded for easier identification. The continuous line represents the wiring connection required for equipment, while the bold type represents the fixture symbol.
For example, the plan above consists of text R1, R2, R3, and so on, close to symbols with a continuous line from one another. The electrical fixture represents the light fixture, and the continuous line represents the wiring connection required from the respective switchboard. To find more fixture details, we would need to refer to the schedules.
Schedules include manufacture, type, model, size, and details of the equipment. Electrical diagrams include schedules for the light fixture, equipment, and load details, as shown in the image below. Schedules help to know details of the equipment or item used on the electrical plans. Components and systems like lighting fixtures and appliances denoted by electrical symbols in electrical diagrams need to be fully described in schedules to estimate, order, and install at the site.
Electrical plans are generally drawn at the same scale as the floor plans. The scale provided on the plan helps to measure the size, length, and distance of equipment. The most common scale is 1⁄4" = 1'-0" (1:50 metric) for residential and small commercial projects, and 1⁄8" = 1'-0" (1:100 metric) for large commercial ones, where electric symbols work. The scale at which the electrical plans are drawn is provided either adjacent to or directly below the drawing title. Sometimes designers might enlarge the detailed and related equipment drawings with their respective scales shown below the drawing.
Note that there are various types of electrical drawings. Electrical circuit drawings often include electrical circuit diagrams to show how electrical components are connected. On the other hand, and electrical connection drawing, or a wiring diagram that shows the location of electrical components. There are also pictorial diagrams that are used solely as a visual representation of an electrical circuit. Keep in mind the different types of electrical diagrams and drawings so that you fully understand the purpose of any diagram you're looking at.
Electrical Plans
Engineers, architects, and electrical contractors are the primary designers of electrical plans. However, interior designers may also make decisions about wire routing and where fixtures like light bulbs or TV equipment are installed.
A designer needs to coordinate a reflected ceiling plan (RCP) like the one pictured below to provide the correct location of light fixtures, registers, and appliances with the other construction trades. Electrical plans include multiple drawings describing the respective layout, such as power distribution layout, panel layout, wiring layout, and fixtures layout. It represents an electrical blueprint and drawing symbol.
The wiring layout consists of wiring routing is a set path for wires. These paths are inside the ceiling and can be seen in a wiring layout. As we can see in the image below, the wiring provided to the light from the switchboard. The conduit layout with junction box installed refers to the drawings available at the site. The ceiling is installed once all the wiring is done.
The details about fixtures, installation methods, or any information necessary to read the drawing are provided in a section of the drawing called plan notes. For example, plan notes might specify the junction box size and wires used: "consider the last point '10. 6x6x4' Junction Box. Run one 2” conduit to roof parapet junction box." This line tells us that the height and width of the junction boxes are 6 inches and depth as 4 inches.
Section drawings like the one pictured below provide more information on how a building, interior space, or equipment is installed. It may be divided into one or more multiple views through the assembly in a vertical direction, taking an imaginary slice through an object or building. Section drawings of electrical plans provide details on heights and relationships between floors, ceilings, spaces, walls, and equipment locations above one another. Two or more sections are often provided at 90 degrees to one another to give additional information.
The commercial buildings consist of multiple similar areas like apartments and hotel rooms. The multiple area floor plans are represented on drawings by a code or reference name on the floor plan. In electrical plans all the wiring layout are found in these plans.
It is helpful to find the correct location of pipes, wires, duct, and fire fighting from the main connection lines. The unit plan provides the detailed view of the electrical layout used in the floor plan of respective area.
The checklist for referring electrical plans are:
Check for the title of the drawing, note its scale, and reference to the orientation or directions.
Check for symbols, abbreviations, and legends.
Readout general notes and respective plan notes for more details.
Refer to schedules or specifications before referring any equipment on the plans.
Check thermostat locations in all the floor plans to coordinate electrical, furniture, and wall layout.
Check the drawings with the reflected ceiling plan (RCP) and other trades drawings to find proper locations and routings.
Check the drawings of panels and connection board to access the power supply for equipment and fixtures.
Check the details, sections, riser diagrams, and enlarged plans for more details.
Finally, during maintenance, refer to the final set of drawings, As-Built drawings.
The electrical floor plans and other electrical plans consist layout of wiring routing, equipment location, and connection point inside the ceiling. The electrical plans include plan notes that consist of additional details required at the time of installation.
