Complete Guide to Electrical Schematic Symbols

Electrical schematic symbols are the universal language of circuit design. Whether you are reading a wiring diagram for a home renovation, debugging an electronics project, or designing an industrial control panel, you need to recognize these symbols instantly. This reference guide covers the most common symbols organized by category, with notes on IEC vs ANSI standards.

Why Standardized Symbols Matter

Imagine trying to read a blueprint where every architect used their own made-up symbols for doors and windows. Electrical schematics would be equally unreadable without standardized symbols. Two main standards govern electrical symbols worldwide:

• ANSI/IEEE (American National Standards Institute / Institute of Electrical and Electronics Engineers): Primarily used in North America. Defined in IEEE Std 315 and related documents.
• IEC (International Electrotechnical Commission): Used internationally, including Europe, Asia, and increasingly in North America. Defined in IEC 60617.

Most modern tools, including CircuitDiagramMaker, support both standards. Knowing which standard applies to your project avoids confusion.

Switches

Switches are among the most frequently used symbols. They control the flow of current by opening or closing a circuit path.

Single-Pole Single-Throw (SPST)

The simplest switch. One input, one output. The ANSI symbol shows a line (contact) that swings open from a pivot point. The IEC symbol is similar but uses a slightly different line style.

• Use: Basic on/off control. Light switches, power switches.
• Symbol key: switch-spst

Single-Pole Double-Throw (SPDT)

One input that connects to one of two outputs. Often used in 3-way light switch circuits.

• Use: Selecting between two circuits, 3-way switching.
• Symbol key: switch-3way

Normally Open Push Button (NO)

A momentary switch that closes the circuit only while pressed. Springs back to open when released.

• Use: Start buttons, doorbells, momentary controls.
• Symbol key: push-button-no

Normally Closed Push Button (NC)

A momentary switch that opens the circuit when pressed. The circuit is closed at rest.

• Use: Stop buttons, safety interlocks.
• Symbol key: push-button-nc

Emergency Stop (E-Stop)

A special NC push button with a mushroom-head actuator, typically red with a yellow surround. Latches when pressed and must be manually reset.

• Use: Emergency shutdown on machinery and control panels.
• Symbol key: emergency-stop

Selector Switch

A rotary switch with multiple positions (2-position, 3-position). Each position connects different circuit paths.

• Use: Mode selection (Auto/Manual), speed selection.
• Symbol key: selector-2pos

Outlets and Receptacles

Duplex Outlet

The standard wall outlet symbol. ANSI shows two parallel lines with a semicircle. IEC uses a different representation.

• Use: Standard 120V receptacle in home wiring diagrams.
• Symbol key: outlet

GFCI Outlet

A Ground Fault Circuit Interrupter outlet. Same as a standard outlet but with GFCI label. Required in bathrooms, kitchens, garages, and outdoor locations.

• Use: Wet/damp locations requiring ground fault protection.
• Symbol key: gfci

Passive Components

Resistor

The ANSI symbol is a zigzag line. The IEC symbol is a simple rectangle. Both are universally recognized.

• Use: Limiting current, voltage division, pull-up/pull-down networks.
• Symbol key: resistor

Capacitor

Two parallel lines (one may be curved for polarized/electrolytic capacitors). Stores and releases electrical energy.

• Use: Filtering, energy storage, timing circuits, coupling/decoupling.
• Symbol key: capacitor

Inductor

A series of loops or bumps. Stores energy in a magnetic field when current flows through it.

• Use: Filters, transformers, energy storage in power supplies, EMI suppression.
• Symbol key: inductor

Potentiometer

A resistor symbol with an arrow pointing to the middle, indicating an adjustable tap.

• Use: Volume controls, brightness adjustment, calibration.
• Symbol key: potentiometer

Semiconductors

Diode

A triangle pointing at a line (bar). Current flows from anode (triangle) to cathode (bar).

• Use: Rectification (AC to DC), reverse polarity protection, signal clamping.
• Symbol key: diode

Zener Diode

Similar to a standard diode but with bent ends on the cathode bar. Designed to conduct in reverse at a specific voltage.

• Use: Voltage regulation, overvoltage protection, voltage references.
• Symbol key: zener-diode

LED (Light Emitting Diode)

A diode symbol with two small arrows pointing away, representing emitted light.

• Use: Indicator lights, displays, illumination.
• Symbol key: led

NPN Transistor

A circle containing a base line, a collector line with an arrow pointing outward from the emitter.

• Use: Switching, amplification. The workhorse of electronics.
• Symbol key: npn-transistor

PNP Transistor

Similar to NPN but with the arrow pointing inward toward the base.

• Use: Switching and amplification in complementary circuits.
• Symbol key: pnp-transistor

N-Channel MOSFET

Shows gate, drain, and source terminals. The arrow on the body indicates channel type.

• Use: Power switching, motor drivers, digital logic.
• Symbol key: n-mosfet

P-Channel MOSFET

Similar to N-MOSFET with the arrow direction reversed.

• Use: High-side switching, load control.
• Symbol key: p-mosfet

Integrated Circuits

Operational Amplifier (Op-Amp)

A triangle with inverting (-) and non-inverting (+) inputs and one output.

• Use: Signal amplification, filtering, comparators, mathematical operations.
• Symbol key: op-amp

Comparator

Similar to an op-amp symbol. Compares two input voltages and outputs high or low.

• Use: Threshold detection, window comparators, zero-crossing detection.
• Symbol key: comparator

Voltage Regulator

Typically shown as a rectangle with three terminals: input, output, and ground.

• Use: Providing stable DC voltage from a higher or varying input voltage.
• Symbol key: voltage-regulator

Logic Gates

AND Gate

A D-shaped symbol. Output is high only when all inputs are high.

• Symbol key: and-gate

OR Gate

A curved, shield-shaped symbol. Output is high when any input is high.

• Symbol key: or-gate

NOT Gate (Inverter)

A triangle with a small circle (bubble) at the output. Inverts the input.

• Symbol key: not-gate

NAND Gate

An AND gate with a bubble at the output. Output is low only when all inputs are high.

• Symbol key: nand-gate

NOR Gate

An OR gate with a bubble at the output. Output is high only when all inputs are low.

• Symbol key: nor-gate

XOR Gate

Similar to an OR gate with an additional curved line at the input. Output is high when inputs differ.

• Symbol key: xor-gate

D Flip-Flop

A rectangle with D (data) and CLK (clock) inputs, Q and Q-bar outputs. Stores one bit of data.

• Symbol key: d-flip-flop

Protection Devices

Fuse

A line passing through a small rectangle or oval. Melts and opens the circuit when current exceeds its rating.

• Use: Overcurrent protection for wiring and equipment.
• Symbol key: fuse

Circuit Breaker (MCB)

A switch symbol with a small rectangle, indicating it can be manually reset after tripping.

• Use: Resettable overcurrent protection. Standard in distribution panels.
• Symbol key: mcb

Thermal Overload Relay

A relay symbol with a thermal element indicator. Opens when current causes excessive heating.

• Use: Motor overload protection. Required by code for most motor circuits.
• Symbol key: thermal-overload

Transformers and Power

Transformer

Two coils (inductors) side by side, separated by parallel lines (representing the core).

• Use: Stepping voltage up or down, isolation, impedance matching.
• Symbol key: transformer

Battery

Long and short parallel lines alternating. The long line is positive, the short line is negative.

• Use: DC power source representation.
• Symbol key: battery

Ground

Three horizontal lines of decreasing length, or a single line with diagonal hatch marks.

• Use: Reference point (0V) for the circuit. Every circuit needs a ground reference.
• Symbol key: ground

Industrial Control Symbols

Contactor Coil

A circle or rectangle labeled with a contactor designation (K1, K2, etc.). When energized, it closes or opens the associated contactor contacts.

• Symbol key: contactor-coil

Contactor NO Contact

A normally open contact associated with a contactor. Closes when the coil is energized.

• Symbol key: contactor-no

Contactor NC Contact

A normally closed contact. Opens when the coil is energized.

• Symbol key: contactor-nc

Relay Coil and Contacts

Smaller version of contactor symbols, used for control-level switching rather than power-level switching.

• Symbol keys: relay-coil, relay-no, relay-nc

Motor Symbols

• 3-Phase Motor: Circle with "3~" or "M" and three connection lines.
• Single-Phase Motor: Circle with "1~" or "M" and two connection lines.
• Symbol keys: motor-3phase, motor-1phase

Pilot Light

A circle with a cross or filled circle, indicating an indicator lamp on a control panel.

• Symbol key: pilot-light

PLC I/O

Rectangles representing PLC input and output modules, with terminal numbers.

• Symbol keys: plc-input, plc-output

VFD (Variable Frequency Drive)

A rectangle labeled VFD or ACS, with input power and output motor connections.

• Symbol key: vfd

IEC vs ANSI: Key Differences

For most practical purposes, both standards are widely understood. However, if you are working on an international project or following a specific code requirement, confirm which standard is expected.

Browse Our 400+ Symbol Library

CircuitDiagramMaker includes over 400 electrical symbols organized across four packs:

• DIY Pack: Outlets, switches, breakers, GFCI, dimmers, and home wiring essentials
• Hobbyist Pack: Resistors, capacitors, LEDs, transistors, Arduino components, and logic gates
• Pro Pack: Op-amps, transformers, voltage regulators, and precision components
• Industrial Pack: 114 symbols including contactors, relays, motors, PLCs, VFDs, thermal overloads, and panel components

Every symbol follows IEC/ANSI standards and includes proper pin connections for wire routing and simulation.

Browse our 400+ symbol library

Key Takeaways

• Electrical schematic symbols follow two main standards: ANSI/IEEE (North America) and IEC (international).
• Switches, resistors, capacitors, diodes, and ground symbols are the most frequently used across all diagram types.
• Industrial diagrams add contactors, relays, motor symbols, and PLC I/O blocks.
• Knowing the difference between NO (normally open) and NC (normally closed) contacts is critical for control circuit design.
• Use a tool with a comprehensive, standards-compliant symbol library to ensure your diagrams are readable by anyone in the industry.