Blueprints and wiring schematics are both critical documents in the electrical industry, but they serve different purposes and present information in distinct ways. In this article, we’re confining our discussion to electrical blueprints.

Circuit Savvy: Practical Tips for Decoding Electrical Blueprints

Steve Maurer, IME
Blueprints and wiring schematics are both critical documents in the electrical industry, but they serve different purposes and present information in distinct ways. In this article, we’re confining our discussion to electrical blueprints.

A blueprint is the comprehensive plan that shows the overall layout of an electrical system within a building. These blueprints are developed and drawn by the architectural firm in charge of the project.
It includes detailed representations of physical spaces, such as rooms and walls, and indicates where electrical components like outlets, switches, and fixtures will be installed. Blueprints are typically used during the planning and construction phases to guide electricians and contractors on how to implement the electrical system within the architectural framework of the building.

Reading electrical blueprints is a fundamental skill for pofessionals in the electrical industry. This article aims to provide a clear and concise overview of the some of the key aspects of electrical blueprint reading, giving you the foundational knowledge needed to confidently approach any project.

We'll cover the following subtopics to ensure a thorough understanding:

  • Understanding symbols and notations
  • Interpreting floor plans and room layouts
  • Tracing electrical circuits
  • Identifying potential issues and conflicts
  • Best practices and tips

Obviously, I can’t go into a lot of intricate detail. But this will give a birds eye view and offer some tips I’ve learned over the years.

Understanding symbols and notations
Electrical symbols are fairly standardized. And if you’re used to working with schematics, you probably recognized most of those used in blueprints. It’s difficult to commit all of them to memory, but no worries. The architectural firm will usually call them out in special notations on the blueprint.

There may be “non standard” notes next to the symbols, also called out in the notations. For example, a D may be used for a dedicated receptacle. But it may also designate a dimmer switch.

Another note might be “AFF” that means above finished floor. This gives a location or dimension not be included on the blueprint.

When in doubt, refer to the notations and legend included with the blueprint package. And I do mean package, because most blueprints for new construction or renovations will have multiple pages, with at least one for each trade. As an electrician, you’re concerned with the electrical prints. However, it’s a good idea to go through and understand the pages for each trade. And if elevation drawings are included, make sure you study them.

That brings us to the next subtopic.

Interpreting floor plans and room layouts
The blueprints for commercial buildings can be quite different than residential dwellings. In commercial installations, the blueprints you’ll refer to are found in the MEP section (mechanical, electrical, plumping). But even with residential blueprints, the information you need will be separated out.

Depending on the engineer or architect, the information provided can range from quite detailed to very sparse. In most cases, you’ll know what to install or rough in, but how you get there is up to you.

Using an architect’s scale ruler can help with some of the placement it the drawing is done to scale (most are). But it’s a good idea to go over elevation drawing and room layouts for more clues.

If kitchen counters are drawn out, for example, you’ll know how high the receptable boxes should be placed. Also, knowing where equipment and appliances are located helps decide if they should be on a dedicated circuit, if not already called out in the notations.

When it’s time to install the actual light fixtures and such, there may be a separate section with the type, brand, and other pertinent information.

But in a nutshell, going over the floor plan and room layouts helps keep do-overs to a minimum.

Tracing electrical circuits
I’m not talking about tracing out live circuits for troubleshooting here. What I mean is tracking out where each device’s circuit originates, what other devices it connect to, and in what order. This also help you plan for efficient home runs back to the power panel or panels.

If they aren’t called out in the blueprint, add them yourself, including the home run. This cuts down on confusion during the actual installation. And it’s easier to map them out, ask questions, and make corrections on paper beforehand.

Cheaper, too.

For example, connecting lighting fixture with dotted lines on the blueprint show groups at a glance. Mark up that blueprint! Make sure you’ve traced every circuit back to the point of origin.

By the way, using a meter after the installation of a circuit or system also identifies errors in installation before they become problems.

Identifying potential issues and conflicts
Engineers and designers are smart people, usually with a boatload of education. But they’re also human and can make mistakes. With extensive projects, the potential for error is greater.

And changes made during construction might not get addressed. That’s why reading and understanding all the sections in the blueprint documents is so important. While residential is fairly easy, commercial and industrial construction has a lot of moving parts. And sometimes… they get moved right in your way.
I’ll bet you’ve never installed a run of conduit and enclosures, only to have the plumbers run ductwork or piping right over the lids and conduit covers, have you.

Additionally, when working with the entrance documents, something, particularly grounding, may not look right or up to code. Be sure to find out why it’s laid out that way, and don’t make changes until you get approval.

Best practices and tips
I’ve alluded to some of these earlier. But they bear repeating. And make sure your team leaders learn and follow them.

General tips:
  • Familiarize yourself with the fundamental elements of electrical blueprints, including symbols, legends, and abbreviations
  • Always check the legends and abbreviations table to understand the symbols and short names used in the plans
  • Have essential tools on hand such as planning software, tape measure, colored pencils and highlighters, graph paper, and an architect’s ruler
  • Have a system in place to mark each run as complete to cut down on confusion and increase efficiency
Reading Electrical Plans
  • Note the title of the drawing and its scale, which helps measure the size, length, and distance of the equipment.
  • Read the general notes provided on the first page for instructions and guidelines.
  • Look for plan notes around the drawing for additional details required during installation
  • Use section drawings to understand the heights and relationships between different parts of the building
A few additional tips
  • Check schedules for details on light fixtures, equipment, and load details.
  • Refer to enlarged plans and sections for more detailed information
  • Begin by studying architectural floor plans to understand the general layout and room names
I love it when a plan comes together. It gives you a sense of pride (and a better paycheck).

Understand how to read and act on electrical blueprints. Make sure your team leaders comprehend them as well. A well-designed blueprint helps ensure an efficiently completed project.

But… only if followed.

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