Reading Schematics and Drawings (Full ver.)

1. Blueprint

Introduction to Blueprints

A blueprint is a technical drawing that serves as a physical map of a building. It details where everything is located and specifies the materials required for construction.

• Synonyms: Floor plan, Reflected Ceiling Plan (RCP).
• Scope: Includes plumbing, electrical layouts, framing, windows, doors, rooms, and appliances.

---

The Electrician’s Perspective

Electricians use blueprints to understand the physical layout and material requirements of a project. These plans are used across two main fields:

1. Architectural: Building structures in residential, commercial, and industrial settings.
2. Engineering: Large-scale infrastructure like roads, bridges, and airport runway lighting.

---

Key Features of Blueprint Sets

Blueprints rarely come as a single page; they are delivered in comprehensive sets.

• Organization: Pages are divided by construction trade (e.g., Electrical, Plumbing) and are typically labeled with letters for easy identification.
• Scale: Since buildings are too large to draw at full size, blueprints are "scaled down."
  • Ratio Scale: A scale of 1:50 means the actual building is 50 times larger than the drawing.
  • Imperial Scale: Found in the Title Block. For example, a 1/4" scale means 1/4 inch on paper equals 1 foot in reality (a ratio of 1:48).

---

Symbols and Legends

Drawing realistic components is too time-consuming, so standardized symbols are used to communicate information quickly.

• Common Electrical Symbols:
  • Receptacles (outlets)
  • Switches (Single-pole, 3-way)
  • Lamp holders
  • Major appliances (Range, Dryer)
• The Legend: This is the "dictionary" for the blueprint. It defines what every symbol means and is usually located on the first sheet of the electrical drawings.
• Notes: These provide specific, additional instructions or details that cannot be captured by symbols alone.

2. Wiring Diagram

What is a Wiring Diagram?

A wiring diagram is a simplified pictorial representation of an electrical system. Unlike a complex schematic, it focuses on the physical location of components and how they are connected.

• Key Function: Shows where components live in a space and the representation of the connections between them.
• Context: These diagrams are part of the electrical plans found within a larger set of blueprints.

---

The Electrician's Use Case

Electricians rely on these diagrams to plan the physical installation of a system.

• Placement: Used to identify the exact spots for lights, switches, and appliances.
• Routing: Helps determine where cables and conduits will run.
• Circuit Logic: Shows how each component connects back to the circuit breaker.

---

Reading the Diagram

To interpret a wiring diagram correctly, you must understand the visual language used:

• Symbols: These represent components (like burners on a stove or outlets in a room).
  • Note: Symbols can vary between different sets of plans. Always check the legend on the first electrical floor plan page.
• Balloons: These icons indicate the specific placement of outlets or fixtures.
• Connecting Lines: These lines show which components are grouped together on a circuit.
• Letter Labels: Lines are often labeled with letters to indicate which specific breaker in the panel they lead back to.

⚠️ Important Warning

The lines on a wiring diagram indicate electrical relationships, not the literal path of the wire. If an electrician installed wires exactly as drawn (straight lines from point A to point B), the wires would be exposed across floors and ceilings. The lines tell you what to connect, not how to route the physical wire through the walls.

---

Comparison: Physical vs. Functional

While wiring diagrams are excellent for showing physical location, they are limited. They focus on where things sit in a structure rather than the deep internal logic of the components themselves.

 

3. Schematics

What is a Schematic?

A schematic is a detailed representation of an electrical circuit's logic. Rather than focusing on where a component is physically located, it focuses on the path of the electrical current.

• Core Elements: Every schematic includes the source (power), conductors (wires), and the load (the device using power).
• Purpose: It shows exactly how electricity travels through a system, making it the primary tool for troubleshooting complex appliances and systems.

---

Schematic vs. Wiring Diagram

It is crucial to understand the difference between these two types of drawings:

Feature	Wiring Diagram	Schematic
Focus	Physical location and general connection.	The logical path of electrical current.
Symbols	Found in the blueprint legend.	Standardized; not usually in the blueprint legend.
Goal	Shows where to install components.	Shows how the circuit functions.

---

Types of Circuits

Schematics illustrate how components are wired together in three primary configurations:

1. Series Circuit: There is only one path for the electrons to flow. If one component fails, the entire circuit is broken.
2. Parallel Circuit: Features multiple branches wired in parallel. Electricity can flow through different paths simultaneously.
3. Combination Circuit: Contains a mix of both series and parallel components.

---

Common Schematic Symbols

Unlike architectural symbols, schematic symbols represent the electrical nature of the component. Common symbols include:

• AC (Alternating Current) and DC (Direct Current)
• Positive (+) and Negative (-) wires
• Resistors: Components that resist the flow of current.
• Coils: Often found in motors or transformers.
• Light Bulbs: The load converted into light.

---

Troubleshooting

When an appliance breaks, technicians use both the wiring diagram and the schematic:

• Use the Wiring Diagram to find where the part is located inside the machine.
• Use the Schematic to understand why the electricity isn't reaching that part or how the circuit is failing.

4. On the Job

1. New Construction: The Planning Phase

When building a house from scratch, an electrician uses the Electrical Floor Plan to move from a drawing to a physical reality.

The Bill of Materials (BOM)

Before any work begins, the electrician creates a Bill of Materials. This is a master list of every single component required for the job.

• Counting: They count every receptacle, switch, and lamp holder marked on the blueprint.
• Ordering Supplies: Common items include:
  • Octagon boxes (for lamp holders)
  • Exhaust fans (e.g., 110 CFM for bathrooms)
  • Wire rolls (75-meter rolls), staples, screws, and wire nuts.

Codes and Specifications

Material choices aren't random; they are dictated by the NEC (National Electrical Code) and local building codes:

• Kitchens/Bathrooms: Require deep boxes to accommodate extra wiring or specific safety devices.
• Outside Walls: Require vapor barrier boxes to prevent air leakage and moisture issues.

---

2. Installation: Working with "Studs"

In a new build, electricians often arrive when only the wooden studs (the wall frame) are up.

• Inferring Measurements: Since the walls aren't finished, electricians must use the floor or ceiling as a reference point to measure where boxes and conduits should be mounted based on the blueprint’s scale.

---

3. Service Calls: Troubleshooting Appliances

When an appliance like a washing machine breaks down, an electrician or technician uses both documents in tandem:

1. The Wiring Diagram (Location): * Purpose: To find where a specific part (like a motor or a sensor) is physically hidden inside the machine's cabinet.
   • Usage: Helps you know which panel to unscrew to access the component.
2. The Schematic (Logic):
   • Purpose: To understand the electrical path connecting those components.
   • Usage: Used with a multimeter to test if electricity is reaching the component or if a switch in the circuit has failed.

---

Summary Table: Document Roles

Task	Blueprint / Floor Plan	Wiring Diagram	Schematic
Material List	Yes (Count components)	No	No
Code Compliance	Yes (Box types/location)	No	No
Finding a Part	No	Yes (Inside appliance)	No
Testing a Circuit	No	No	Yes (Logic/Path)