Electrical Symbols Guide
A complete reference for electrical symbols used in circuit diagrams, schematics, and wiring plans. Find unit symbols like Ω (ohm), learn keyboard shortcuts, and identify standard schematic and NEC wiring diagram symbols.
Electrical Unit Symbols
These are the standard symbols and Greek letters used for electrical quantities, units, and formulas. You will encounter them on multimeters, in NEC code references, on nameplates, and in engineering documentation.
| Symbol | Name | Unit / Usage | HTML Entity |
|---|---|---|---|
| Ω | Omega (Ohm) | Resistance — ohms (Ω) | Ω |
| V | Volt | Voltage / electromotive force (V) | V |
| A | Ampere | Current (A) | A |
| W | Watt | Power (W) | W |
| F | Farad | Capacitance (F) | F |
| H | Henry | Inductance (H) | H |
| Hz | Hertz | Frequency (Hz) — cycles per second | Hz |
| Φ | Phi (Phase) | Phase angle; power factor angle | Φ |
| Δ | Delta | Delta connection (3-phase); change in value (ΔV) | Δ |
| θ | Theta | Phase angle in AC circuits; angle of impedance | θ |
| π | Pi | Mathematical constant (3.14159…); used in AC frequency and impedance calculations | π |
| μ | Mu (Micro) | Metric prefix for 10⁻⁶ — e.g., μF (microfarad), μA (microamp) | μ |
| Σ | Sigma | Summation — used in load calculations and power formulas | Σ |
How to Type the Ohm Symbol (Ω)
The ohm symbol Ω (uppercase Greek omega) is the most commonly searched electrical symbol. Here is every way to type or insert it:
| Method | How To | Result |
|---|---|---|
| Mac Keyboard | Press Option + Z | Ω |
| Windows (Alt Code) | Hold Alt, type 234 on the numeric keypad, release Alt | Ω |
| HTML Entity | Type Ω in your HTML code | Ω |
| HTML Numeric | Type Ω or Ω | Ω |
| Unicode | U+2126 (Ohm Sign) or U+03A9 (Greek Capital Letter Omega) | Ω |
| Copy & Paste | Select and copy this symbol: Ω | Ω |
Tip:Unicode defines two code points that look identical — U+2126 (“Ohm Sign”) and U+03A9 (“Greek Capital Letter Omega”). They render the same glyph. The official SI recommendation is to use U+03A9, but both are universally accepted in electrical documentation.
Common Circuit Schematic Symbols
These symbols are used in circuit schematics and electrical engineering drawings per IEEE/ANSI standards. Understanding them is essential for reading any circuit diagram.
| Symbol Name | Description |
|---|---|
| Resistor | Zigzag line (ANSI) or rectangle (IEC). Opposes current flow and is measured in ohms (Ω). Used in voltage dividers, current limiting, and pull-up/pull-down circuits. |
| Capacitor | Two parallel lines (non-polarized) or one flat line and one curved line (polarized/electrolytic). Stores energy in an electric field, measured in farads (F). Commonly shown as μF or pF. |
| Inductor | Series of curved bumps or loops resembling a coil. Stores energy in a magnetic field, measured in henrys (H). Found in filters, transformers, and motors. |
| Transformer | Two inductors (coils) side by side with parallel lines between them representing the core. Transfers energy between circuits via magnetic coupling. Labeled with turns ratio (e.g., 10:1). |
| Diode | Triangle pointing toward a vertical line (cathode bar). Allows current flow in one direction only. The triangle points in the direction of conventional current flow (anode to cathode). |
| LED (Light-Emitting Diode) | Same as diode symbol with two small arrows pointing away from it, representing emitted light. Current flows from anode to cathode; requires a current-limiting resistor. |
| Switch (SPST) | A break in a line with a lever or movable contact. Single Pole, Single Throw (SPST) is the simplest form — one input, one output, on or off. Variants include SPDT, DPST, and DPDT. |
| Fuse | Small rectangle or an S-shaped curve inside a box. An overcurrent protection device that melts open when current exceeds its rating, breaking the circuit. Rated in amps. |
| Ground | Three horizontal lines of decreasing length stacked vertically (earth ground), or three diagonal lines (chassis ground). Represents the reference point (0V) in a circuit. |
| Battery | Alternating long (positive) and short (negative) parallel lines. A single pair represents one cell; multiple pairs represent a multi-cell battery. The longer line is always the positive terminal. |
| AC Source | Circle with a sine wave (~) inside. Represents an alternating current power source such as a wall outlet or generator. Standard residential AC in the US is 120V/60Hz. |
| DC Source | Circle with a plus (+) and minus (−) sign, or a straight line and dashed line inside. Represents a direct current power source like a battery or DC power supply. |
| Motor | Circle with the letter “M” inside. Converts electrical energy to mechanical energy. Additional markings may indicate AC/DC type, horsepower, or phase configuration. |
Electrical Wiring Diagram Symbols
These symbols appear on residential and commercial wiring diagrams, blueprints, and NEC-based construction drawings. Electricians and contractors use them to plan installations and pass inspections.
| Symbol Name | Blueprint Notation | Description |
|---|---|---|
| Duplex Outlet (Receptacle) | ○ with two parallel lines | Standard 120V duplex receptacle. A circle with two short tangent lines. Placed on walls at 12″ above finished floor per standard practice. NEC Article 210.52 governs spacing. |
| Single-Pole Switch | S | Controls a light or load from one location. Shown as the letter “S” on blueprints. Installed at 48″ above finished floor. Connected to the hot (black) wire only. |
| Three-Way Switch | S₃ | Controls a light from two locations. Shown as “S” with a subscript 3. Requires two three-way switches and a traveler wire pair. Common at hallways, staircases, and large rooms. |
| GFCI Outlet | GFI or GFCI | Ground-fault circuit interrupter receptacle. Shown as a standard outlet symbol with “GFI” or “GFCI” label. Required by NEC in kitchens, bathrooms, garages, outdoors, and within 6 feet of sinks. |
| Light Fixture (Ceiling) | ⊕ | A circle with lines radiating from center, or a circle with a cross inside. Variations indicate fixture type: fluorescent (rectangle), recessed can (circle with “R”), or track lighting. |
| Junction Box | J or ■ | A point where wires are spliced and protected. Shown as a filled dot or small square with “J”. Must remain accessible per NEC Article 314.29. All splices must be enclosed in a listed junction box. |
| Electrical Panel (Loadcenter) | Rectangle with vertical line | Main distribution panel or sub-panel. Shown as a rectangle with internal divisions representing breaker spaces. Labeled with amperage rating (e.g., 200A) and number of circuits. |
| Electric Meter | Circle with “kWh” | Utility meter that measures energy consumption in kilowatt-hours. Located at the service entrance between the utility feed and the main panel. Shown as a circle with “kWh” inside. |
| Disconnect Switch | Rectangle with “DISC” | A safety switch used to de-energize equipment for maintenance. Required by NEC within sight of HVAC units, water heaters, and other fixed equipment. Shown as a rectangle or switch symbol labeled “DISC.” |
Frequently Asked Questions
What is the ohm symbol?
The ohm symbol is Ω (uppercase Greek letter omega). It represents the unit of electrical resistance named after German physicist Georg Simon Ohm. In HTML, you can write it as Ω and its Unicode code point is U+2126. One ohm is defined as the resistance between two points when a constant potential difference of one volt produces a current of one ampere.
How do I type the omega symbol on keyboard?
On Mac, press Option+Z to type Ω. On Windows, hold Alt and type 234 on the numeric keypad (Alt+234), then release Alt. In HTML documents, use Ω for uppercase or ω for lowercase. You can also copy and paste the symbol: Ω. In Microsoft Word, go to Insert > Symbol > Greek and Coptic.
What are the basic electrical symbols?
The basic electrical symbols include: resistor (zigzag line), capacitor (two parallel lines), inductor (series of loops), battery (alternating long and short parallel lines), switch (break in a line with a lever), ground (three horizontal lines decreasing in length), diode (triangle pointing to a line), and fuse (rectangle or S-curve). These symbols are standardized by IEEE and IEC for use in circuit diagrams.
What is the symbol for ground?
The electrical ground symbol consists of three horizontal lines of decreasing length stacked vertically, connected to a vertical line from the circuit. There are also variations: chassis ground uses three diagonal lines, and earth ground uses three horizontal lines. In wiring diagrams, ground connections are typically shown as a green or bare copper wire connected to the grounding bus.
What does the triangle symbol mean in electrical?
The triangle symbol (delta, Δ) in electrical work represents a delta connection in three-phase power systems. In a delta configuration, three components are connected end-to-end forming a triangle shape, as opposed to a wye (Y) configuration. Delta connections are common in industrial motors and transformers. The delta symbol is also used in formulas to represent “change in” a value, such as ΔV for voltage drop.
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