Switches and ground symbols
Switch symbols show the contacts in their resting (unoperated) state. A line that is angled away from a contact point is open; a line touching it is closed.
| Symbol | Meaning | How it is drawn | Unicode |
|---|---|---|---|
| SPST switch | single pole, single throw: one circuit, on or off | a line hinged at one terminal, angled away from a second terminal | none |
| SPDT switch | single pole, double throw: one input selects one of two outputs | a hinged line that can touch either of two terminals | none |
| DPST / DPDT switch | two poles operated together | two single-pole switches joined by a dashed line | none |
| Push button, normally open (NO) | closes only while pressed | a bar held above two contacts by a stem, not touching them | none |
| Push button, normally closed (NC) | opens only while pressed | a bar resting across two contacts | none |
| DIP switch | a bank of small SPST switches in one package | a row of SPST switches, often boxed and numbered | none |
| Relay | a switch operated by a coil | a rectangle (coil) linked by a dashed line to a switch contact | none |
| Earth ground | connection to the earth | a vertical line ending in three horizontal lines of decreasing length | ⏚ U+23DA EARTH GROUND |
| Chassis (frame) ground | connection to the metal enclosure | a horizontal line with short slanted strokes beneath it, like a rake | none |
| Signal or common ground | the circuit's 0 V reference | commonly a downward-pointing triangle or a single bar | none |
Sources: IEC: IEC 60617 Graphical symbols for diagrams (database); Unicode Consortium: Miscellaneous Technical (U+2300–U+23FF) code chart
Passive component symbols
Resistor, capacitor and inductor symbols are where the IEC and IEEE conventions differ most visibly.
| Symbol | Meaning | How it is drawn |
|---|---|---|
| Resistor | fixed resistance | IEC: a small open rectangle on the wire. IEEE/ANSI: a zigzag line |
| Variable resistor | adjustable resistance | the resistor symbol with a diagonal arrow drawn through it |
| Potentiometer | three-terminal adjustable divider | the resistor symbol with an arrow (the wiper) pointing at its side |
| Thermistor | resistance that changes with temperature | the resistor symbol crossed by a diagonal line with a short horizontal foot, often marked t° |
| Capacitor | stores charge | two short parallel lines (plates) with a gap between them |
| Polarized (electrolytic) capacitor | capacitor with a + and − terminal | one plate straight and the other curved (IEEE), or a + sign beside one plate |
| Variable capacitor | adjustable capacitance | the capacitor symbol with a diagonal arrow through it |
| Inductor (coil) | stores energy in a magnetic field | a row of connected loops or semicircles |
| Iron-core inductor | inductor wound on a magnetic core | the coil symbol with one or two straight lines drawn alongside it |
| Transformer | two magnetically coupled coils | two coils facing each other, with parallel lines between them for an iron core |
| Fuse | opens when current is too high | IEC: a small rectangle with the wire running through it; some American drawings use an S-shaped curve instead |
Sources: IEC: IEC 60617 Graphical symbols for diagrams (database)
Semiconductor symbols: diodes and transistors
A diode symbol is a triangle pointing toward a bar. The triangle is the anode side and the bar is the cathode; conventional current flows in the direction the triangle points. For bipolar transistors the arrow is always on the emitter and points in the direction of conventional current: out of the device for NPN, into it for PNP.
| Symbol | Meaning | How it is drawn |
|---|---|---|
| Diode | conducts in one direction | a triangle pointing at a perpendicular bar |
| Light-emitting diode (LED) | diode that emits light | the diode symbol with two small arrows pointing away from it |
| Photodiode | diode that responds to light | the diode symbol with two small arrows pointing toward it |
| Zener diode | conducts in reverse at a set voltage | the diode symbol with the bar bent into a Z-like shape at its ends |
| Schottky diode | low forward-voltage diode | the diode symbol with the bar ends hooked into an S shape |
| NPN transistor | bipolar transistor, current flows collector to emitter | a base line with collector and emitter leads; the emitter arrow points outward |
| PNP transistor | bipolar transistor, current flows emitter to collector | the same outline; the emitter arrow points inward, toward the base |
| N-channel MOSFET | field-effect transistor switched by gate voltage | a gate line separated by a gap from the channel, with an arrow on the body pointing in |
| P-channel MOSFET | field-effect transistor, opposite polarity | the same outline with the body arrow pointing out |
Sources: IEC: IEC 60617 Graphical symbols for diagrams (database)
Meters and power sources
Meters are drawn as a circle containing the letter of what they measure. Sources distinguish DC from AC and voltage from current.
| Symbol | Meaning | How it is drawn | Unicode |
|---|---|---|---|
| Voltmeter | measures voltage, connected in parallel | a circle containing V | none |
| Ammeter | measures current, connected in series | a circle containing A | none |
| Ohmmeter | measures resistance | a circle containing Ω | Ω U+2126 OHM SIGN |
| Wattmeter | measures power | a circle containing W | none |
| Cell | a single electrochemical cell | a long thin line (positive) beside a short thick line (negative) | none |
| Battery | several cells in series | two or more cell symbols in a row, or one cell with a dashed gap | none |
| DC voltage source | constant voltage supply | a circle with + and − marks | ⎓ U+2393 DIRECT CURRENT SYMBOL FORM TWO |
| AC voltage source | alternating voltage supply | a circle containing one cycle of a sine wave | ⏦ U+23E6 AC CURRENT |
| Current source | constant current supply | a circle containing an arrow showing the current direction | none |
| Lamp | light bulb or indicator | a circle containing an X (IEC) or a loop filament | none |
| Power (standby) symbol | on/off control marking on equipment | a broken circle with a vertical line | ⏻ U+23FB POWER SYMBOL |
Sources: IEC: IEC 60617 Graphical symbols for diagrams (database); Unicode Consortium: Miscellaneous Technical (U+2300–U+23FF) code chart