Electrical and electronic symbols are graphical representations of electrical and electronic components and devices used in circuit diagrams. They allow for the visual communication of complex circuit and wiring information in a standardized way. This article will provide a full introduction to the most common electrical and electronic symbols, their meanings and applications.
Overview of Electrical and Electronic Symbols
Electrical symbols represent items such as batteries, wires, resistors, inductors, switches, transformers, transmitters, receivers, meters, and capacitors. Electronic symbols represent electronic devices and components in circuits including diodes, transistors, integrated circuits, and logic gates.
Standardized sets of symbols ensure that anyone reading a circuit diagram can understand the circuit and how it functions regardless of language or location. Using clear, universally recognized symbols improves communication and avoids errors arising from misunderstandings.
There are different standards for electrical and electronic symbols, but the International Electrotechnical Commission’s (IEC) standards are the most widely adopted worldwide. The IEC 60617 standard covers graphical symbols for diagrams, while the IEC 617-12 standard specifically covers symbols and designations for semiconductor devices.
In the United States, the American National Standards Institute (ANSI) also publishes guidelines on electrical and electronics symbols and how they should be used. While less common globally, ANSI standards are still important for electrical work in the US.
Key Types of Electrical and Electronic Symbols
Some of the most essential categories of symbols to be familiar with include:
Passive Component Symbols
- Resistor – Impedes current flow. Varying resistances are signified by color bands.
- Capacitor – Stores electric charge. Varying capacitances are signified by number markings.
- Inductor -Stores energy in magnetic field. Varying inductances are signified by number markings.
Active Component Symbols
- Battery – Supplies electrical energy. Longer lines indicate higher voltage.
- Voltage Source – Supplies electrical energy. Signifies AC or DC with waves or straight lines.
- Current Source – Supplies constant electrical current. Arrow shows direction of current flow.
Switch and Relay Symbols
- SPST Switch – Single pole, single throw. Opens or closes circuit.
- SPDT Switch – Single pole, double throw. Connects common terminal to one or the other terminal.
- Relay – Electrically operated switch. Uses electromagnet to open or close contact terminals.
Transducer and Measuring Device Symbols
- Microphone – Converts sound to electrical energy.
- Loudspeaker – Converts electrical energy to sound.
- Thermocouple – Converts temperature to electrical voltage.
- Ammeter – Measures electric current.
Logic Gate Symbols
- AND Gate – High output only if all inputs are high.
- OR Gate – High output if any input is high.
- NOT Gate – Inverts input signal.
- XOR Gate – High output if inputs differ.
Transistor Symbols
- NPN Bipolar Junction Transistor – NPN transistor allows current flow when base is active.
- PNP Bipolar Junction Transistor – PNP transistor blocks current flow unless base is active.
- N-Channel JFET – N-channel junction gate field effect transistor.
- P-Channel JFET – P-channel junction gate field effect transistor.
Diode Symbols
- Regular Diode – Allows current flow in one direction only.
- Light Emitting Diode – Diode that emits light.
- Zener Diode – Allows current flow in reverse direction when above breakdown voltage.
- Schottky Diode – Fast switching diode with low forward voltage drop.
Connector and Mechanical Symbols
- Wire – Conducts electrical current.
- Connector – Joins wires, PCB traces, or components.
- Ground/Earth – Reference point for voltage.
- Chassis Ground – Connects to metal chassis containing circuitry.
- Fuse – Protects against excessive current.
Overview of Circuit Schematic Symbols
Circuit schematics show the components in an electrical or electronic circuit and their relationships using standardized symbols. Schematics allow technicians and engineers to design, build, troubleshoot and modify circuits efficiently.
Some key things that circuit schematic symbols convey include:
- The types of components and their values
- How components connect to each other
- The flow of current through the circuit
- Electrical interactions between components
- Logical functions for digital circuits
To be effective, circuit schematic diagrams need to be clear, readable and accurately represent the physical circuit based on established symbol conventions. Well-drawn schematics allow for easy visual tracing of circuit operation and aids analysis through abstraction.
Circuit schematics range from simple wiring diagrams to complex system diagrams. They are an essential tool for all electrical engineering disciplines including electronics, telecommunications, control systems, power, and more.
Here is a simple example schematic showing some key types of symbols:<img src=”https://www.conceptdraw.com/How-To-Guide/picture/electrical-engineering-symbols/Electrical-Symbols-Circuit-Schematic-Symbols.png” alt=”example schematic” width=”400″ height=”300″>
This schematic shows the standard symbols for an AC voltage source, ground, resistor, LED, and switch wired in a simple circuit. The lines between symbols show how they are electrically connected.
Symbol Variations and Multiple Standards
While standards exist for most electrical and electronic symbols, there can be variations in how the symbols are drawn. Small differences may exist between geographic regions or functional domains. Within a single organization, custom variations may also develop on standard symbols over time.
Some examples of symbol variations include:
- Ground symbols may use single or multiple horizontal lines
- Zener diode symbols may show reversed polarity with different line styles
- Voltage source symbols may be drawn with or without added plus/minus polarity markings
- Integrated circuit chip outlines may vary in proportion and complexity
Even with variations, most symbols will follow the core design principles needed to identify the type of component or device. But when working with new schematics, it is important to verify any less familiar symbols used.
The other challenge is differences between published symbol standards. While the IEC standards are the most internationally recognized, ANSI and JIC standards are still used for some North American electrical work. Key symbols are very similar between IEC and ANSI standards but small differences can exist.
Again, when transitioning between companies or geographies it helps to identify which standards are in use and adapt to any different conventions present. Most electrical engineering software and tools allow switching symbol sets as needed.
Reading and Interpreting Circuit Schematics
Being able to accurately read and follow circuit schematics is an essential skill for electrical engineers and technicians. Here are some key tips on working with circuit schematics effectively:
- Learn the standardized symbols – Be familiar with all commonly used schematic symbols for electrical and electronic components. Recognizing symbols instantly aids circuit analysis.
- Trace current flow – Mentally trace the path current will flow through the circuit. Visualize interactions between components.
- Map functions – On digital schematics, map how combinations of logic gates implement higher level functions.
- Check connections – Verify all connections between symbols are valid and that the circuit is electrically complete.
- Find key nodes – Identify voltage nodes, ground points, power inputs, and other key circuit nodes. These aid analysis.
- Label unclear elements – If the meaning of any symbol or section is unclear, label or highlight it for future follow up.
- Consider signal flow – For mixed analog and digital schematics, trace both power flow as well as signal flow through the system.
- Compare with physical layouts – Cross-reference schematics with hardware photos and layout diagrams to validate and expand mental model.
- Summarize functions – Document the key purpose and functionality of each section, component, and the overall system.
With practice, reading schematics becomes second nature. Always reference the original schematic when analyzing or troubleshooting a circuit – mental models alone can be faulty.
Schematic Design Best Practices
Creating high-quality schematics requires knowledge of symbol standards as well as visual communication and diagramming skills. Here are some best practices to follow when drawing circuit schematics:
- Use standard symbols – Symbols should be immediately recognizable to any electrical engineer.
- Label all components – Include value/rating and other component details as text labels.
- Draw connections clearly – Use thick lines between component terminals with junction dots. Avoid crossing unconnected wires.
- Arrange components thoughtfully – Group related components. Logical flow from left to right. Minimal wire crossings.
- Clarify signal flow – Indicate input and output points on subcircuits. Show key signal paths.
- Add reference designators – Label each component with a unique letter/number identifier.
- Include power and grounds – Show all power inputs and ground points for the circuit.
- Add schematic borders and metadata – Title block with designer, date, version, etc. Page numbers if multi-page.
- Highlight plugs/connectors – Show all external wiring connections.
- Add functional blocks – Use dotted boxes to group components into functional sections.
- Limit nesting – Break out complex sections into separate simplified schematics.
Following schematic best practices takes some additional time but greatly improves the understandability and usability of the diagrams. Poor schematics are a frequent source of errors in manufacturing and troubleshooting.
Electrical Engineering Software for Schematics
Specialized software tools are invaluable for efficiently creating and working with circuit schematics. Some capabilities provided by electrical engineering software include:
- Extensive libraries of standard symbols
- Drag-and-drop placement of symbols
- Auto-routing of connection lines between terminals
- Validation checks on designs
- Bill of Materials (BOM) generation
