The 4 Types of Wiring Diagrams

Last updated August 12, 2024
Wiring diagrams depict electrical circuits in multiple formats so electricians and engineers can visualize their projects at different levels of detail. Each of these formats provides a view of an electrical system specified for different purposes. Some are outlines for the arrangement of main components and others are specific directions for constructing a circuit.
This guide lists the four most common types of wiring diagrams, their purposes and how to read them
Table of Contents
What Are the Types of Wiring Diagrams?
How to Read Block Diagrams
How to Read Circuit Diagrams
How to Read Schematic Diagrams
How to Read Ladder Diagrams
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What Are the Types of Wiring Diagrams?

A wiring diagram represents the conductors and components that make up an electrical circuit or system. Some wiring diagrams simply show how electricity flows through the circuit, while others show how each connection must be made for the circuit to work.
Wiring diagrams can take many forms, and each provides instructions on how to set up or maintain an electrical system. These are the most common types of wiring diagrams:
- Block diagrams only show the main components and are used for planning electrical systems.
- Circuit diagrams represent every component and connection in a circuit for wiring installation.
- Schematic diagrams show how electricity flows through a circuit and use standardized symbols to map circuits.
- Ladder diagrams represent how a device's programming interacts with its wiring.
Electricians use wiring diagrams at almost every stage of their work. Block diagrams and schematics are usually drawn when planning or installing a new electrical system. Circuit and ladder diagrams are used for maintenance, changes or additions to an existing system.
How to Read Block Diagrams

A block diagram is the first stage of planning a complex circuit. It uses interconnected blocks to represent the main components and their relationships. Engineers use block diagrams as flow charts that describe hardware details in the simplest terms.
Block diagrams do not show information about the placement of individual wires and components. Smaller components in an electrical system may be omitted from block diagrams. Block diagrams are meant to provide a key to the flow of processes within the system.
The symbols in a block diagram include:
- Block: Each block is labeled with a major component in the circuit. Each block only has one input and one output.
- Line: A line connects two blocks in a system to show their relationship.
- Arrow Line: This symbol denotes the flow of data or a signal through an electronic device.
Due to the simplified nature of block diagrams, some may be more difficult to read without an understanding of the subject matter. Discuss this with project managers or engineers as needed to learn about each component and its purpose.
Block diagrams start with the leftmost component, which is usually a fuse or power supply. Follow the power source's connections to further components, such as a doorbell and porch light.
Pro Tip: Keep an extra copy of your project's block diagram and write notes on it when designing more detailed representations.
How to Read Circuit Diagrams

A circuit diagram, often known simply as a wiring diagram, is a graphical representation of a single circuit. Circuit diagrams depict the connections between electrical components to illustrate their functions. They provide a reference point for electricians diagnosing problems in electrical systems, and help engineers experiment when designing new systems.
Diagrams usually represent individual circuits in pictorial format. However, they also represent each circuit in a system by electrical schematics. Each type of circuit diagram shows the connections within a circuit, but they differ in how they present information.
Circuit diagrams can depict nearly every type of circuit in an electrical system, such as:
- Lighting, such as 3-way light switches and dimmers
- Electrical outlets and receptacles
- Appliance outlets, such as washers, dryers and cooking ranges
- Thermostats
Pictorial circuit diagrams provide a visual representation of electrical components and the wire that connects them. These diagrams show the physical layout of the components and use different colors to indicate the types of wire used. Components are usually represented by drawings or icons.
For example, a 3-way light switch uses two light switches, one light fixture, and four types of wire. Three wires connect the first light switch to the rest of the room and the breaker box or the power source. The white or neutral wire passes all the way through to the lightbulb. The grounding cable connects to each component in the circuit.
The black or hot wire connects to the common screw on the light switch. Black and red wires also connect the two light switches and the lightbulb using the black traveler terminals.
How to Read Schematic Diagrams

Schematic circuit diagrams, or schematics, use a set of standardized electrical symbols to represent components and connections. These diagrams depict the flow of current with more specificity than other wiring diagrams, because they cover entire electrical systems. Schematics do not omit any components and often depict how each circuit connects to the rest of the electrical system.
The first step in reading schematics is to familiarize yourself with standard electrical symbols and which components they represent. As seen in the example above, the most common symbols for electrical components include:
- Power source
- Resistors
- Capacitors
- Transistors
- Wires
The next step in reading schematics is to find the power source. This is represented by a circle with two lines extending from it, labeled as the positive and negative terminals. Look for connections to the power source, such as resistors, inductors, diodes or buzzers. For example, a resistor is represented by a rectangle in the middle of a connection. Capacitors are depicted as a broken line separated by two horizontal lines.
Connections between components link the positive and negative terminals of each component. Lines represent wired connections. However, connections made by contact such as switches and buttons are drawn as circles at the end of a wire called nodes.
Schematics usually display the power source at the top, and the output or load at the bottom. Schematics may also include annotations and labels that provide additional information on the circuit, such as component values or specifications. For example, a laundry center with an above average amperage or voltage may have an annotation letting electricians know to allocate more power.
How to Read Ladder Diagrams

Ladder diagrams are a type of schematic specialized for documenting industrial control logic systems, or programmable logic controllers (PLCs). They resemble a ladder in that they have two vertical rails indicating positive and negative power, and a horizontal line for each control circuit in the diagram. Ladder diagrams use the same electrical symbols as common schematics, and read from top to bottom, left to right.
Each horizontal line, or “rung,” on a ladder diagram represents a complete circuit that starts and ends at the power supply. Lines connect the components in each circuit, and the arrows indicate electrical flow just as they do in other types of wiring diagrams. Components in ladder diagrams are broken into two groups called contacts and coils.
- Contacts represent the input signals such as those from sensors or switches.
- Coils represent output signals from such output devices as actuators and relays.
Contacts are set up in one of two states, which are normally open (NO) and normally closed (NC). These refer to the state of a contact in a circuit before user input. For example, light switches should be represented as NO contacts, because the circuit is open until a person flips the switch. Conversely, a motion sensor in a home security system should be an NC contact, because it is always sensing for motion while active.
Ladder logic diagrams use Boolean logic, which means they only recognize circuits as being on or off.
The rungs are evaluated top to bottom, and the output devices are considered on or off depending on the state of the input devices.
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