Electrical Skills - Wiring Diagram Practice
- SkillCat Team
- Apr 1, 2025
- 9 min read
Updated: Dec 23, 2025
Basic Wiring: Chapter 2
Wiring Diagrams
In this module, we will review wiring diagrams. You will learn how to use a wiring diagram to wire a system. Skip to quiz!
Types of Diagrams
You want to master electrical work? Start here. Understanding electrical diagrams isn’t just helpful—it’s absolutely critical. Electricians rely on these diagrams to understand, install, and troubleshoot industrial electrical systems, ensuring safety, compliance, and efficiency. These diagrams are your roadmap to every circuit, every connection, and every solution you’ll ever need. Master them, and you master the trade.
Here’s what you need to know about the main diagram types:
Wiring diagrams show you exactly where every wire goes and how every device connects. You use these for installation and troubleshooting because they map out the real-world layout. No guesswork. No confusion.
Schematic diagrams cut through the clutter with standardized symbols for resistors, capacitors, switches, and relays. They focus on function and energy flow, not physical placement. Learn to read these, and you understand how any circuit actually works.
Ladder diagrams dominate industrial control systems for good reason. They’re built like a ladder—power at the top, load at the bottom—with horizontal and vertical lines showing current flow and component positions. Simple. Logical. Effective.
Industrial electrical diagrams visually represent the electrical system, showing the interconnections between components such as transformers, generators, motors, and control devices.
You’ll also work with single-line diagrams and block diagrams for complex systems. Single-line diagrams compress entire electrical systems into one clear path, so you spot main components fast. Block diagrams break systems into functional modules, making complicated relationships crystal clear.
Every diagram uses standardized symbols and notation—usually IEC standards. This means you can read any diagram, anywhere, from any electrician or engineer. That zigzag line? Always a resistor. Those specific symbols? They mean switches, fuses, batteries, and every other device you’ll encounter.
You troubleshoot faster when you read diagrams like a pro. Follow the current flow, trace component connections, and you pinpoint faults in minutes, not hours. You find the right answer quickly and get systems running efficiently. Less downtime. Fewer problems. Better results.
Diagrams transform your training too. They give you the visual tools to understand complex circuits, practice real troubleshooting scenarios, and build the skills that matter. Whether you’re starting out or advancing your career, reading and creating wiring diagrams, schematic diagrams, and ladder diagrams puts you ahead of the competition. Various resources, including training programs, books, and online tutorials, are available to help you learn to read and interpret industrial electrical diagrams.
Bottom line: electrical diagrams drive everything you do in this field. Design, installation, operation, maintenance—it all starts here. Master these diagrams, and you gain the power to identify, test, and fix any electrical problem that comes your way. You ensure safe, efficient performance every time. This isn’t just technical knowledge—this is your path to success in the electrical trade.
Components
Recall that a wiring diagram is a blueprint of an electrical system. Wiring diagrams display:
The components in a system,
The wiring and
The flow of current
Relays and contactors are common components in wiring diagrams. These devices use a coil, which when energized, creates a magnetic field that actuates the contacts to open or close circuits.
There are a few types of wiring diagrams, including:
Ladder diagrams, and
Schematic diagrams
For wiring, you will mainly use a schematic diagram. Being able to read a schematic diagram is one of the most important skills for wiring.
The schematic diagram will tell us what components are in the system. The diagram will also show us the wiring between each component. The contactor coil is represented by a specific symbol and is used to control high-voltage loads such as fans and compressors by energizing or de-energizing the contacts.
Recall that a schematic diagram uses symbols to represent a component. In the image, you can see the symbols for a dual run capacitor, start capacitor, and a start thermistor. The form of process switches, such as level, pressure, or temperature switches, is also indicated in diagrams, showing their normal state and how they operate under different conditions.
You can also see the wiring between each component. In this image, a “YEL” wire runs from the start capacitor to the COM terminal on the dual run capacitor. “YEL” stands for a yellow wire. Components like relays or switches are often connected using two terminals, and it is important to identify each point of connection in the circuit for proper wiring and troubleshooting.
Recall that wiring diagrams have:
Factory wiring, and
Field wiring.
Factory wiring has already been installed by the manufacturer. Any wires that are factory installed have already been wired.
Field wiring is wiring that must be done in the field. Any wire that is labeled field wiring must be connected by you.
For each drawing, it is important to consider the function of the circuit.
Component Connections
Recall that we separate wiring into three categories:
Hot wires,
Neutral wires, and
Ground wires
Each wire has a different job in the circuit.
Each component in the circuit will need to have a hot wire. The hot wire is typically black or red. Some components in the circuit will need to have a ground and a neutral wire.
In control circuits, such as those for air compressor motors, a manual switch is often included to allow manual operation in addition to automatic controls like pressure switches.
Wiring diagrams for HVAC systems frequently include circuits for heat elements, such as heating coils or sequencers. It is important to correctly wire and identify these heat-related components to ensure proper operation and safety.
Recall that the hot wire delivers power to each component. You can think of the hot wire as delivering power from the source to the entrance of the component.
Recall that the neutral wire connects the last component in the circuit back to the power source. The neutral wire creates a complete path for current to flow.
Recall that the ground wire connects the circuit to the earth. The ground wire protects us if the system has a short circuit.
Series/Parallel
Recall that components can be wired in two ways:
Series, and
Parallel
A wiring diagram shows you if components are wired in series or parallel. Determining the wiring configuration is essential for troubleshooting, as it helps you use measurement tools like a multimeter to diagnose issues accurately. During troubleshooting, you may need to perform specific tests or procedures to understand how the system operates or to identify faults.
Recall that components wired in series only have one path for current to flow. The current moves from the exit of one component directly to the entrance of the next component. If a fault occurs in any component in a series circuit, it can interrupt the entire current path and affect the operation of all components in the series.
For example, look at the diagram to the right. You can see that there are three switches.
These switches are in series with each other. There is only one path for current to flow once it exits a switch.
Components can also be wired in parallel. Recall that components in parallel have multiple paths for current to flow. When troubleshooting parallel circuits, determining the exact location of a fault is important, as a problem in one branch may not affect the others.
For example, look at the schematic diagram to the right. The OFM, COMP, and SR are wired in parallel. Current can flow through three paths once it exits the “21” terminal of the contactor.
Reading a Diagram
In the picture to the right, you can see a schematic diagram. Recall that a schematic diagram shows the wiring and components of a system.
L1 and L2 are the wires which go to and from the power source. L1 is the hot wire. It carries 120V to the components. L2 is the neutral wire. It carries 120V back to the source.
In this graphic, you can see the hot wire (L1) enters on the left side of the schematic. L1 brings power to the 11 terminal of the contactor switch. L1 also brings power to the CHS.
This same pattern continues throughout the diagram. The hot wire will carry the voltage to each component in the diagram.
L2 acts as the neutral wire for the circuit. You can find the neutral wire in the diagram at terminal 23 of the contactor.
On this diagram, you will find the ground wire symbol in the top left corner. You will also find a grounding symbol on the outdoor fan motor (OFM).
Note that the schematic diagram also includes the color of the wires. Above each wire you will see a label like “YEL” which stands for a yellow wire. “YEL/BLU” stands for a yellow and blue wire.
In this module, we explained the importance of a wiring diagram for wiring. The wiring diagram will show you the components in a system and how they are wired.
After reading and interpreting a wiring diagram, it is important to be able to report your findings and observations, especially after troubleshooting or testing a circuit. This demonstrates your understanding and proper troubleshooting procedures.
Troubleshooting Electrical Systems
Troubleshooting electrical systems separates real electricians from wannabes. When systems fail and components stop working, you need to diagnose fast and get it right. Performance, safety, and downtime all depend on your skills. You master this by knowing wiring diagrams, schematic diagrams, and every single component in that circuit.
Start with the wiring diagram or ladder diagram. Study it like your paycheck depends on it—because it does. These diagrams show you exactly how every device, switch, and connection works. They map out how electrical energy flows from power source through each component. Follow those lines and symbols. Find each device position, trace the hot wire path, and locate the ground wire. Miss this step and you risk short circuits and safety hazards.
Faults happen. Short circuits hit. Relays malfunction. You grab your multimeter and test voltage, continuity, and resistance at every critical point. Contactor coil won't energize? Check voltage at both terminals. Inspect for loose connections. Use that schematic to trace the control circuit. Know what each symbol means—that zigzag line for a resistor, that specific form for a capacitor. This knowledge pinpoints problems fast.
IEC standards make your job easier, not harder. They keep symbols and wiring conventions consistent across every diagram you'll see. You can identify a fuse, relay, or diode in any schematic from any manufacturer. Blue wire versus yellow wire matters. Ground terminal location matters. Get these basics right and you work safely and accurately every time.
Components interact. Master electricians know this. That faulty relay stops your load from operating. That blown fuse cuts electrical energy to an entire module. Analyze the diagram. Determine which components connect in series or parallel. Understand how one branch fault affects the whole system. This knowledge saves you hours of guesswork.
Real troubleshooting goes beyond finding faults—you figure out why they happened. System overloaded? Switch failed from heat or wear? Polarity problem at a terminal? Ask these questions. Use your training. Fix the immediate issue and prevent future problems. That's what professionals do.
Document everything after you identify and repair the fault. Report the problem, your steps, and materials used. This shows your expertise and creates valuable resources for future maintenance. Smart electricians build knowledge bases that make them indispensable.
Master troubleshooting by combining circuit knowledge, diagram reading, and component expertise with hands-on testing. Use the right tools. Understand diagrams and standards completely. Work methodically. You'll identify, test, and fix faults in any electrical system. Safe, reliable operation follows naturally when you know what you're doing.
Question #1: A schematic diagram displays:
Components in a system
Wiring between components
Both
Scroll down for the answer...
Answer: Both
A schematic diagram displays the components and wiring in an electrical system.
Question #2: Factory wiring is wired:
In the field
By the manufacturer
By the business owner
All of the above
Scroll down for the answer...
Answer: By the manufacturer
Factory wiring has been done by the manufacturer. All products they sell will come with factory wiring pre-installed.
Question #3: Field wiring is wired:
On the job site
By the manufacturer
By the business owner
All of the above
Scroll down for the answer...
Answer: On the job site
Field wiring is done on the job site. Field wiring is what you must wire in order for a system to function.
Question #4: Components in series have:
One path for current to flow
Two paths for current to flow
Multiple paths for current to flow
Both “B” and “C”
Scroll down for the answer...
Answer: One path for current to flow
Wires in series have only one path for current to flow. It will move from the exit of one component directly to the entrance of the next component.
Question #5: Components in parallel have:
One path for current to flow
Multiple paths for current to flow
Scroll down for the answer...
Answer: Multiple paths for current to flow
Components in parallel have more than one path for current to flow.
Question #6: L1 and L2 are:
Your power source
Components
Contactors
Relays
Scroll down for the answer...
Answer: Your power source
L1 and L2 are the incoming power for the system. L1 acts as the hot wire. L2 is the neutral wire.
Other References: