CEA Reading Electrical Blueprints Questions and Answers — Questions and Answers
Question 1: An apprentice is reviewing a set of electrical blueprints for a commercial building and needs to find detailed information about the circuit breaker sizes, the loads served by each circuit, and the total connected load for Panel 'LP-1'. In which part of the blueprints would this information most likely be found?
- The Symbol Legend
- The Site Plan
- The General Notes
- The Panelboard Schedule (Correct answer)
Correct answer: The Panelboard Schedule
Panelboard schedules are dedicated tables on electrical drawings that provide a detailed breakdown of each circuit within a specific panel. They list the circuit number, breaker size and type, wire size, phase connection, a description of the load (e.g., 'receptacles - office 101'), and the calculated load in volt-amperes.
Question 2: While looking at an electrical floor plan, an apprentice sees a symbol consisting of a circle with two short, parallel lines drawn through it, located on a wall. What does this standard symbol typically represent?
- A lighting outlet
- A duplex receptacle (Correct answer)
- A smoke detector
- A single-pole switch
Correct answer: A duplex receptacle
This is a standard symbol used on electrical blueprints in North America to represent a common duplex receptacle, which is the type of outlet used for general purpose plug-in devices.
Question 3: An apprentice is tasked with determining the required length of a home run from a receptacle to the panel as shown on a floor plan. The plan has a noted scale of 1/4" = 1'-0". If the apprentice measures the distance on the paper to be 7.5 inches, what is the actual horizontal distance of the run?
- 15 feet
- 22.5 feet
- 30 feet (Correct answer)
- 37.5 feet
Correct answer: 30 feet
With a scale of 1/4" = 1'-0", every full inch on the drawing represents 4 feet in reality (1 divided by 1/4 = 4). Therefore, the actual distance is calculated by multiplying the measured inches by 4 feet/inch: 7.5 inches * 4 feet/inch = 30 feet.
Question 4: On an electrical drawing set, which document provides a simplified overview of the power distribution system, showing the path of power from the utility service to panelboards and major equipment, without showing the physical location of the components?
- A Floor Plan
- An Elevation Drawing
- A One-Line Diagram (Correct answer)
- A Lighting Fixture Schedule
Correct answer: A One-Line Diagram
A one-line diagram (also called a single-line diagram) is specifically designed to show the logical connections and flow of a power system in a simplified format. It uses single lines and symbols to represent the entire system, from the power source to the final distribution panels and large equipment.
Question 5: During an installation, an apprentice notes that the electrical drawings call for Type NM cable for a circuit, but the project's written specifications explicitly require that the same circuit be installed in EMT conduit. In a case of conflict between the drawings and the specifications, which document is generally considered to take precedence?
- The written specifications, as they provide detailed requirements. (Correct answer)
- The electrical drawings, as they are the primary visual guide.
- Whichever method is less expensive to install.
- The apprentice should request clarification via an RFI.
Correct answer: The written specifications, as they provide detailed requirements.
In standard construction contract hierarchy, the written specifications provide a higher level of detail and requirements and generally govern over the drawings in case of a direct conflict. While submitting a Request for Information (RFI) is the correct procedural step to resolve the conflict, the specifications are considered the governing document.
Question 6: Which of the following pieces of information is most likely to be found on an electrical site plan rather than on a building's floor plan?
- The location of wall-mounted duplex receptacles in the offices.
- The mounting height of a fire alarm horn/strobe in a corridor.
- The circuit number for the breakroom lighting.
- The routing of underground feeders from the utility transformer to the building. (Correct answer)
Correct answer: The routing of underground feeders from the utility transformer to the building.
A site plan shows the entire property, including the building's position, property lines, and connections to external utilities. The path of underground conductors from a pad-mounted utility transformer to the building's main electrical service is a key piece of information found on the site plan. The other options are interior details found on floor plans.
CEA Reading Electrical Blueprints Questions and Answers
An apprentice is reviewing a set of electrical blueprints for a commercial building and needs to find detailed information about the circuit breaker sizes, the loads served by each circuit, and the total connected load for Panel 'LP-1'.
In which part of the blueprints would this information most likely be found?