Wire
Also: conductor
A line is a wire. Its length and bends on the drawing mean nothing; only what it connects matters.
Electrical and circuit symbols
Circuit diagrams and wiring diagrams use the same small set of symbols. Learn about 60 of them and you can read almost any schematic, from a car stereo to a solar setup.
Two standards are in use. The US uses ANSI/IEEE symbols (a zigzag resistor), while Europe, the UK, Australia and most of Asia use IEC 60617 (a box resistor). Where they differ, both are shown.
Free. In draw.io, open the library with File › Open Library from › Device. Each symbol below also downloads as SVG, or copies straight into draw.io.
Wires and grounds
Wires joined
Also: junction, node
A dot where lines meet means the wires are connected.
Wires crossing, not joined
Lines that cross without a dot are not connected.
Wires crossing (hop)
An older way to show wires that cross without connecting. You still see it in car and appliance manuals.
Terminal
Also: connection point, test point
An open circle marks a point where an outside wire connects, or a point to measure.
Earth ground
Also: ground, earth
A connection to the earth: a ground rod, or the earth pin of a mains socket. Fault current flows here.
Signal ground
Also: common, 0 V
The 0 V reference of a circuit. Every ground symbol on a schematic is connected to every other one.
Chassis ground
A connection to the metal frame or case. In cars the body is the negative return, so most loads are wired to it.
Terminal block
Also: terminal strip
A row of screw terminals where wires are joined. Each box is one terminal.
Power sources
Cell
One battery cell. The long line is positive (+), the short line negative (−).
Battery
Several cells in series. Drawings rarely show the real count: a 12 V battery is often drawn with two or three cells.
DC voltage source
Also: power supply
A source of constant voltage, such as a bench power supply. The + marks the positive terminal.
AC voltage source
Alternating voltage, such as mains power or a signal generator. The wave inside means AC.
Current source
Pushes a fixed current, whatever is connected, in the direction of the arrow. Mostly seen in textbooks and analog design. Some European drawings use two overlapping circles instead.
Solar cell
Also: PV cell, photovoltaic
Turns light into DC power. The arrows show light coming in. A whole solar panel is drawn the same way.
Resistors
Resistor (US)
Also: ANSI resistor, zigzag
Limits current. The value is written next to it in ohms: 220R, 4k7 (4.7 kΩ), 1M.
Resistor (IEC)
Also: European resistor, box
The same part, drawn as a box in Europe and most of the world.
Potentiometer (US)
Also: pot, variable resistor
A resistor with a sliding contact (the arrow), like a volume knob. It has three terminals.
Potentiometer (IEC)
The same part in IEC style.
Thermistor
Also: NTC, PTC, nonlinear resistor
Its resistance changes with temperature; the bent line marks that. Used as a temperature sensor. Often labelled t°.
Varistor
Also: MOV, VDR, surge protector
Conducts hard above a set voltage. Placed across a mains input, it absorbs spikes.
Capacitors, coils and transformers
Capacitor
Two plates that store charge. It blocks DC and passes AC. Values are in farads: 100 nF, 10 µF.
Electrolytic capacitor
Also: polarized capacitor
Must go in the right way round: + to the higher voltage. The curved plate is negative. Fitted backwards, it can burst.
Inductor
Also: coil, choke
A coil of wire that resists changes in current. Values are in henries: 10 µH, 1 mH.
Transformer
Two coils that pass AC from one circuit to another, stepping the voltage up or down. The lines between them mean an iron core.
Transformer (IEC)
The short IEC form: two overlapping circles, one per winding. Common on power and single-line diagrams.
Crystal
Also: quartz, oscillator
Sets an exact frequency, the clock for a microcontroller or a watch.
Diodes and transistors
Diode
Current flows one way only, in the direction of the arrow. The bar is the cathode, the stripe on the real part.
LED
Also: light-emitting diode
A diode that lights up. The arrows point out. It needs a resistor in series to limit the current.
Zener diode
Used the "wrong" way round to hold a fixed voltage, such as 5.1 V. The bent ends of the bar mark it.
Schottky diode
A fast diode that loses less voltage (about 0.3 V). Common in power supplies and solar chargers. The S-shaped bar marks it.
Photodiode
A diode that conducts when light falls on it. The arrows point in. Used as a light sensor.
NPN transistor
A small current into the base switches a larger current from collector to emitter. The emitter arrow points out.
PNP transistor
The same with the polarity reversed. The emitter arrow points in. It turns on when the base is pulled low.
N-channel MOSFET
Voltage on the gate switches current from drain to source. The usual choice for switching a load to ground.
P-channel MOSFET
Turns on when the gate is pulled below the source. Often used to switch the positive side of a load.
N-channel JFET
A transistor that is on until the gate voltage pinches it off. Found in low-noise audio and sensor amplifiers.
Switches and relays
Switches and contacts are drawn in their rest position: as they are when nothing is pressed and no power is applied.
Switch, open
Also: SPST, on/off switch
A simple on/off switch, drawn off. Current cannot flow until it is closed.
Switch, closed
The same switch, drawn on.
Push button
Also: momentary switch
Connects only while pressed, like a doorbell.
Changeover switch
Also: SPDT, two-way switch
Connects the common terminal to one of two outputs, for example to pick between two batteries.
Selector switch
Also: rotary switch
Connects the common terminal to one of several positions.
Isolator
Also: disconnector, battery switch
Cuts a whole circuit off so it is safe to work on. Not designed to switch under load.
Relay
A switch worked by a coil. A small current through the coil (the box) closes the contact; the dashed line links them.
Relay coil
The coil on its own. Its contacts are drawn elsewhere and carry the same name, such as K1.
Normally open contact
Also: NO, make contact
Open at rest. Closes when the relay is energized or the button is pressed.
Normally closed contact
Also: NC, break contact
Closed at rest. Opens when the relay is energized.
Fuses and breakers
Fuse (IEC)
A thin wire that melts when the current is too high, so the wire it protects does not overheat. Rated in amps.
Fuse (US)
The same part in the US style.
Circuit breaker (US)
Trips on too much current, like a fuse, but can be reset.
Circuit breaker (IEC)
The IEC form: a switch with a cross on its contact.
Lamps, motors and meters
Lamp
Also: light, indicator lamp
Any light: a cabin light, a headlight, a warning lamp. The circle with a cross is the most common form.
Light bulb (US)
An older US symbol for an incandescent bulb: the loop is the filament.
Motor
A circle with M. A fan, a pump, a wiper or a winch motor.
Generator
Also: alternator
A circle with G. On a car or boat diagram, this is the alternator.
Loudspeaker
Turns an electrical signal into sound.
Antenna
Also: aerial
Sends or receives radio signals.
Ammeter
Measures current. Wired in series with the load, so the current flows through it.
Voltmeter
Measures voltage. Wired across the part, in parallel.
Chips and logic gates
Logic gates work with two levels: 1 (on, high) and 0 (off, low). A small circle on an output means the result is inverted.
Op-amp
Also: operational amplifier
Amplifies the difference between its + and − inputs. Power pins are often left off the drawing.
Voltage regulator
Turns a higher, changing voltage into a steady one, for example 12 V in, 5 V out (7805, LM317).
AND gate
Output is 1 only when all inputs are 1.
OR gate
Output is 1 when at least one input is 1.
NOT gate
Also: inverter
Output is the opposite of the input.
NAND gate
AND with an inverted output: 0 only when all inputs are 1.
NOR gate
OR with an inverted output: 1 only when all inputs are 0.
XOR gate
Also: exclusive OR
Output is 1 when the two inputs differ.
Buffer
Output equals input. Used to give a weak signal more drive.
How to read a circuit diagram
Start at the power source and follow the wires to each part and back to ground or the negative terminal. Current only flows around a closed loop.
Parts are named with a letter and a number. The value is written next to them. The letters are standard, so a quick look tells you what is on the board:
| Letter | Part | Example |
|---|---|---|
| R | Resistor | R1 = 10k |
| C | Capacitor | C3 = 100 nF |
| L | Inductor | L1 = 22 µH |
| D | Diode (LED often LED1) | D2 = 1N4007 |
| Q | Transistor or MOSFET | Q1 = 2N2222 |
| U or IC | Chip | U1 = NE555 |
| K | Relay | K1 |
| F | Fuse | F1 = 5 A |
| S or SW | Switch | SW1 |
| J or X | Connector | J2 |
Wiring diagram or schematic?
A schematic (circuit diagram) shows how parts are connected electrically, laid out to be easy to follow. It says nothing about where the parts sit.
A wiring diagram shows real wires between real parts: which terminal, which wire colour, often the wire size. Car, boat and house wiring is usually drawn this way. Both use the symbols above.
Drew a circuit by hand?
Take a photo of the sketch. Sketch2scheme redraws it with these symbols as a clean, editable diagram you can download for draw.io, as PNG or as SVG.
Questions
Why do some resistors look like a zigzag and others like a box?
They are the same part. The zigzag is the US (ANSI/IEEE) symbol; the box is the IEC symbol used in Europe and most other countries. Both mean resistor.
Are lines that cross connected?
Only if there is a dot where they meet. Lines that cross without a dot are separate wires. Older drawings show a small hop where one wire jumps over the other.
What is the difference between earth, chassis and signal ground?
Earth ground connects to the earth itself and carries fault current. Chassis ground connects to the metal frame or case. Signal ground is the 0 V reference of a circuit. In many small circuits they are all the same point, but on mains equipment and in vehicles they are kept apart on purpose.
Can I use these symbols in my own drawings?
Yes. Download the SVG of any symbol, or the whole set as a draw.io library, and use them in documents, homework or product manuals. The shapes come from draw.io, which is open source.
More symbol charts
Symbols are drawn with draw.io (diagrams.net), which is open source. Use them freely in your own drawings, documents and lessons.