Control Circuits, Diagrams & Code Calculations
Electrical diagrams, switching circuits, fire alarm requirements, Class 2 circuits, demand factors, and dwelling service load calculations.
- Distinguish between schematic, wiring, ladder, and one-line diagrams
- Explain three-way and four-way switching circuit operation
- Describe CEC fire alarm and smoke alarm requirements for dwelling units
- Identify Class 2 circuit voltage limitations per the CEC
- Apply demand factors to dwelling service load calculations
Lección 1
Schematic, Wiring & Ladder Diagrams
Types of Electrical Diagrams
Electricians work with several types of electrical diagrams, each serving a different purpose. The exam will test your ability to identify which diagram type is used for what purpose.
Schematic Diagram
Shows: Electrical connections and function
Layout: Logical arrangement, not physical
Used for: Understanding circuit operation
Components: Standard electrical symbols
Wiring Diagram
Shows: Physical location of components
Layout: Reflects actual equipment positions
Used for: Installation and routing
Components: Realistic representations
A wiring diagram shows the physical location of components. Unlike a schematic that focuses on electrical function, a wiring diagram represents where components are physically mounted and how wires are actually routed. This makes wiring diagrams essential for installation and troubleshooting work.
Ladder Diagrams
A ladder diagram (also called a line diagram or elementary diagram) arranges the circuit in a format that resembles a ladder. Two vertical power rails (L1 and L2) form the sides, and horizontal rungs show individual control circuits.
Ladder diagrams are the standard format for industrial motor control circuits because they:
- Show the sequence of operation clearly
- Make troubleshooting logical (follow each rung independently)
- Separate power circuits from control circuits
- Present the circuit in order of operation from top to bottom
One-Line Diagrams
A one-line diagram (also called a single-line diagram) uses a single line to represent three-phase circuits. It provides an overview of the entire electrical distribution system, showing:
- Service entrance and main disconnect
- Transformers and their ratings
- Switchgear and distribution panels
- Feeders and major branch circuits
- Protective device ratings
A wiring diagram shows the physical location of components. Schematic diagrams show electrical function. Ladder diagrams are the standard for industrial control circuits. One-line diagrams provide a system overview. Each type serves a specific purpose in design, installation, and troubleshooting.