What do the symbols on a wiring diagram mean?

Wiring diagrams are essential tools used in electrical engineering to visually represent the connections and components of an electrical system. These diagrams use various symbols to convey information about the circuitry, allowing engineers, technicians, and electricians to effectively understand and troubleshoot the system. Understanding the symbols used in schematic diagrams is critical for anyone involved in electrical work. In this article, we will explore the meaning behind these symbols and their importance in interpreting schematic diagrams.

1. Basic Symbols

When examining a schematic, it is important to become familiar with the basic symbols used to represent common electrical components. These symbols provide a standardized visual representation for easy identification. Some of the basic symbols include

  • Resistor: Represented by a zigzag line, resistors are passive components that resist the flow of electrical current.
  • Capacitor: Shown as two parallel lines, capacitors store and release electrical energy.
  • Inductor: Shown as a coil of wire, inductors store energy in a magnetic field.
  • Switch: Depicted as a simple line with a break, switches control the flow of current within a circuit.
  • Transformer: Shown as two coils, transformers change voltage levels between different parts of a circuit.
  • Diode: Shown as a triangle with a line through it, diodes allow current to flow in one direction and block it in the opposite direction.

These are just a few of the many symbols used in schematic diagrams. It is important to consult a reference guide or legend specific to the schematic you are working with to determine the exact meaning of each symbol.

2. Power supply symbols

Power supply symbols are used to represent different sources of electrical power within a circuit. These symbols indicate how electrical power is generated and delivered to the system. Some of the common power supply symbols are

  • Battery: Represented by two parallel lines, batteries are a portable source of direct current (DC) power.
  • Generator: Shown as a circle with a vertical line and arrows, generators produce alternating current (AC) power.
  • Outlet: Indicated by a circle with two parallel lines, outlets provide AC power from the electrical grid.
  • Solar Cell: Shown as a square with diagonal lines, solar cells convert sunlight into direct current.

Understanding these power symbols is essential to identifying power sources and their connections within a circuit. This knowledge helps engineers and electricians determine how power is distributed and used in the system.

3. Connection Symbols

The connection symbols in a schematic represent the various ways in which components are connected within a circuit. These symbols illustrate the paths that electrical current follows and help visualize the flow of electricity. Some common connection symbols are

  • Wire: Represented by a line, wires carry electrical current between components.
  • Junction: Shown as a dot where multiple wires intersect, junctions indicate a point of connection.
  • Ground: Indicated by a horizontal line with three smaller lines branching downward, the ground symbol represents the reference point for voltage in a circuit.
  • Bus: Shown as a thick line, buses are used to connect multiple wires or components.

By interpreting these connection symbols, professionals can understand how components are connected, identify potential points of failure, and ensure proper circuit functionality.

4. Control and protection symbols

Control and protection symbols in schematic diagrams are used to represent devices and mechanisms responsible for controlling and protecting the electrical system. These symbols illustrate switches, relays, and fuses that enable proper operation and prevent damage. Some examples of control and protection symbols include

  • Switch: Represented by a simple line with a break, switches control the flow of current within a circuit.
  • Relay: Shown as a rectangle with an arrow, relays are electromagnetic switches controlled by an external signal.
  • Fuse: Shown as a squiggly line, fuses are safety devices that break the circuit when the current exceeds a certain threshold, protecting components from damage.
  • Circuit Breaker: Depicted as a switch-like symbol, circuit breakers automatically interrupt the flow of current when a fault occurs.
  • Motor: Shown as a circle with the letter “M,” motors convert electrical energy into mechanical motion.

Understanding these control and protection symbols is critical to ensuring the safety and proper functioning of electrical systems. By interpreting these symbols correctly, professionals can identify the components responsible for controlling the system and take appropriate measures to protect against faults and overloads.

5. Special symbols

In addition to the basic symbols, power supply symbols, connection symbols, and control and protection symbols, there are special symbols used in circuit diagrams to represent specific components or functions. These symbols are often specific to certain industries or applications. Some examples of special symbols are

  • Microcontroller: Represented by a rectangle with the letters “MCU,” microcontrollers are integrated circuits used to control digital systems.
  • Sensor: Shown as a rectangle with a diagonal arrow, sensors detect and measure various physical quantities.
  • Amplifier: Shown as an inward-pointing triangle, amplifiers increase the amplitude of electrical signals.
  • Antenna: Shown as a set of concentric circles or a zigzag line, antennas transmit or receive electromagnetic signals.

These specialized symbols address specific needs and applications in various fields of science and technology. Understanding these symbols allows professionals to accurately interpret and design complex systems in their respective fields.


Wiring diagrams are essential tools for understanding and working with electrical systems. The symbols used in these diagrams provide a standardized language for representing components, connections, power sources, controls, and protective devices. By becoming familiar with these symbols, engineers, technicians, and electricians can effectively analyze, design, and troubleshoot electrical circuits. Whether it’s deciphering the meaning of basic symbols or understanding specialized symbols for specific applications, a comprehensive knowledge of schematic symbols is essential for anyone involved in electrical engineering.

Remember, when working with schematics, always refer to the accompanying legend or reference guide specific to the schematic you are using to ensure accurate interpretation of the symbols.


What do the symbols on a wiring diagram mean?

The symbols on a wiring diagram represent various electrical components and devices, providing a standardized visual language for understanding and interpreting electrical circuits. Each symbol represents a specific function or type of component, allowing engineers, electricians, and technicians to analyze and troubleshoot electrical systems.

Why are symbols used on wiring diagrams?

Symbols are used on wiring diagrams to convey information quickly and accurately. Instead of using lengthy descriptions or technical language, symbols provide a concise representation of electrical components and their connections. This simplifies the understanding of complex electrical systems, facilitates communication, and enables efficient troubleshooting and maintenance.

What are some common symbols used on wiring diagrams?

Common symbols used on wiring diagrams include:

  • Lines and arrows representing electrical connections and conductors
  • Circles or dots indicating junction points or connection points
  • Squares or rectangles representing electrical devices or components
  • Zigzag lines representing resistors
  • Diagonal lines representing capacitors
  • Triangles representing transformers
  • Various shapes and configurations for switches, relays, fuses, and other control devices

These are just a few examples, and there are many more symbols used depending on the complexity and specific requirements of the electrical system being represented.

Can symbols on wiring diagrams vary between different industries or regions?

Yes, symbols on wiring diagrams can vary between different industries or regions. While there are standardized symbols used in many countries, specific industries or regions may have their own variations or additional symbols based on their unique requirements or regulations. It is important to consult the appropriate standards and guidelines when interpreting wiring diagrams for a particular application.

Where can I find a key or legend that explains the symbols on a wiring diagram?

A key or legend that explains the symbols used on a specific wiring diagram can usually be found within the diagram itself or in the accompanying documentation. The key provides a detailed description of each symbol used, including its meaning, function, and any additional information necessary for understanding the diagram. If a key is not readily available, referring to industry standards or consulting with professionals experienced in reading wiring diagrams can help in deciphering the symbols.

Are there software tools available to create and interpret wiring diagrams with symbols?

Yes, there are software tools available that facilitate the creation and interpretation of wiring diagrams with symbols. These tools typically provide a user-friendly interface where users can drag and drop symbols onto a canvas, connect them with lines to represent electrical connections, and generate professional-looking diagrams. Additionally, these software tools often include features such as automatic symbol libraries, error checking, and the ability to generate reports or export diagrams in various formats.