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
| Symbol | ANSI/IEEE | IEC |
|---|---|---|
| Resistor | Zigzag line | Rectangle |
| Fuse | Oval element | Rectangle with wire |
| Motor | Circle with M | Circle with M (similar) |
| Relay coil | Circle | Rectangle |
| Ground | Three lines | Single line with hatch |
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
Schematic vs Wiring Diagram vs One-Line Diagram
These three diagram types use the same symbol set but represent different information. A schematic (also called a line diagram or ladder diagram in control work) shows the electrical logic of a circuit -- how components connect functionally -- without regard to their physical location. A wiring diagram shows the same circuit arranged to match the physical layout of the equipment, including terminal numbers, wire colors, and cable routing, so an installer can connect real wires to real terminals. A one-line diagram (single-line diagram) simplifies a three-phase power system down to a single line representing all three phases, used for power distribution overviews rather than detailed component wiring. Knowing which type you are looking at tells you what questions it can answer -- a schematic tells you how the circuit works, a wiring diagram tells you where to connect the wires.
Worked Example: Reading a Motor Start/Stop Control Circuit
A standard motor control ladder diagram uses several of the symbols above together. Reading it from left to right: the circuit starts at one supply rail (L1) and ends at the other (L2 or neutral). The normally closed Stop push button connects first -- current can flow through it at rest, since it stays closed until pressed. Next comes the normally open Start push button, wired with a normally open contactor auxiliary contact in parallel across it -- this is the seal-in (holding) contact. When the Start button is pressed momentarily, current reaches the contactor coil, energizing it. The contactor's auxiliary NO contact closes at the same time, creating a parallel path around the Start button so the coil stays energized after the button is released. Pressing Stop breaks the circuit at any time, de-energizing the coil and opening both the main power contacts and the seal-in contact. A thermal overload relay's NC contact is typically wired in series with the coil as well, so sustained overcurrent on the motor trips the overload and drops out the coil even if nobody presses Stop.
Common Symbol Reading Mistakes
Mixing up NO and NC contacts. A relay or contactor symbol drawn with a small gap represents a normally open contact, closed only when energized; a symbol drawn with a diagonal line through a closed gap represents normally closed, open only when energized. Misreading one for the other is one of the most frequent errors in control circuit troubleshooting.
Reading diode direction backwards. The triangle points in the direction of conventional current flow when forward biased, toward the bar (cathode). It is easy to read the triangle as pointing away from current flow if you are used to thinking in terms of electron flow instead.
Assuming a wire crossing is a connection. Two crossing lines are only electrically connected if a solid dot marks the intersection. Many schematics draw one wire as a small arc or hop over the other specifically to show no connection -- but not every drawing style uses the hop, so always check for the dot.
Skipping the legend. Some manufacturers use nonstandard or simplified symbol variants in their own documentation. Check for a legend or symbol key on the drawing before assuming a symbol matches the standard version.
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.
Frequently asked questions
What does a dashed line mean in an electrical schematic?
A dashed line usually represents a mechanical link rather than an electrical connection -- for example, ganged switch contacts operated by the same handle, or an interlock between two devices. Dashed lines are also used to outline an enclosure or panel boundary, showing which components are grouped inside the same box.
Is there a separate symbol for a neutral wire versus a ground wire?
Ground has its own dedicated symbol (the three-line or hatched earth symbol), but neutral conductors are usually just drawn as ordinary wire lines labeled N. In residential wiring diagrams, neutral is distinguished by its white or gray wire color and label rather than by a unique graphical symbol.
Why does a relay symbol sometimes show 8 pins?
An 8-pin 'ice cube' relay is a DPDT (double-pole double-throw) relay -- two independent sets of common, normally open, and normally closed contacts plus two coil pins. The schematic shows this as one coil symbol with two separate contact symbol pairs, both labeled with the same relay designator.
Can you mix ANSI and IEC symbols in the same schematic?
It is technically possible since both standards represent the same electrical functions, but it is bad practice. Symbols like the resistor and relay coil look completely different between the two standards, and mixing them in one drawing makes it harder for anyone else to read consistently. Pick one standard per project.
If a switch symbol is drawn open, does that mean it's normally open in use?
Not necessarily -- schematics show switches, relays, and contacts in their de-energized, unpressed, or unactuated resting state, not their normal operating state. A switch drawn open could be a normally open switch at rest, or a normally closed switch shown open because the diagram depicts an actuated condition. Check the labeling.