Symboles électriques

The shorthand a wiring diagram is written in. There are 35 marks here, grouped by what the thing does — a switch is a switch whether a hand, a coil or the daylight throws it — and each one says what it means in one line and points at a live diagram on this site that uses it. Keep this page open beside the diagrams until the marks stop needing names.

A symbol is a drawing convention, so it can be taught here freely. What a device must connect to, how big it must be and what colour its conductors are is set by the code, not by the mark.

Switches
Receptacles
Sources
Loads
Protection
Conductors and junctions
Controls and sensors
Look-alikes
Drill: which symbol is this?

Three things every mark here obeys

A filled dot is a terminal. A place a conductor lands — on a switch, a receptacle, the supply.
Copper is the part that moves or senses. The blade, the button bar, the joint. Never a wire colour.
A dot at a crossing means joined. No dot, the lines only cross. Read this one before any other.

Switches

Things a hand operates. The blade is copper because it is the part that moves; a dot is a terminal the wire lands on.

Single-pole switch One conductor, made or broken by a tilted blade. Drawn open, as here; closed, the blade would lie flat on the second dot. The one every other switch is built from. It belongs in the hot, never the return. See it: Single-pole switch wiring →
Three-way switch (SPDT) One common on the left, two travellers on the right. The blade always touches one traveller or the other — there is no off. The common is the odd terminal out. Hot lands on one common, the lamp feed on the other; travellers run between. See it: 3-way switch wiring diagram →
Four-way switch Two travellers in, two out. In one position it passes them straight through; in the other it swaps them over. It never breaks the circuit on its own. Always between two three-ways. Count terminals: four means four-way. See it: 4-way switch wiring diagram →
Pushbutton, normally open A bar held above two terminals by a spring. Press it and the bar bridges them; let go and it lifts. Momentary — it does not stay. This is a Start button. Nothing flows through it until a finger is on it. See it: Motor start/stop station →
Pushbutton, normally closed The bar rests on both terminals and carries current until you press it, which lifts it off. Momentary — release and it closes again. This is a Stop button. It is the one that is closed while nobody is touching it. See it: Motor start/stop station →
Two-pole switch Two blades on one handle, opening two conductors at the same instant. The dashed tie is the mechanical link between them. Used wherever both conductors to a load are live — a 240 V load has no neutral to leave in place. See it: 240 V receptacle wiring →

Receptacles

Outlets as they appear on a plan: a circle at the wall, with slots that say which kind. The short line is the wall.

Duplex receptacle A circle at the wall with two slots — two places to plug in, both fed together. The short line is the wall it mounts on. Its terminals are live whether or not anything is plugged in. See it: Duplex receptacle wiring →
Single receptacle One slot: one place to plug in. Drawn where a single dedicated outlet is meant, not a duplex. See it: Duplex receptacle wiring →
Split receptacle A duplex with the tab broken: the two halves are fed separately. The copper half is the switched one; the other is always live. Same device as a duplex on the outside. The difference is a broken tab you cannot see from the front. See it: Split receptacle wiring →
GFCI receptacle An outlet with test and reset buttons — the device that compares the current going out with the current coming back and opens if they differ. Line side in, load side out. Get them backwards and nothing downstream is protected. See it: GFCI wiring diagram →
240 V receptacle A circle with angled slots and a round pin: an outlet fed by two live legs, with no neutral. The slots are shaped so an ordinary plug cannot go in. See it: 240 V receptacle wiring →

Sources

Where the pressure comes from. Every trace on this site starts at one of these and ends back at it.

Supply / source A box with two terminals. The pressure goes out on one and comes home on the other. Every diagram here starts at one. The copper terminal is the hot. On a drawing the source is usually on the left, so you read left to right. See it: Hot, neutral, ground →
AC source A circle with one cycle of a wave inside: a supply whose voltage swings back and forth. The mains is this. See it: Hot, neutral, ground →
Battery (DC source) Long and short bars: a supply that pushes one way only. The long bar is the positive end. Control circuits, doorbells and meters live here; the wiring diagrams on this site are AC. See it: Ohm's law practice →
Transformer Two coils facing each other across a pair of bars. Power crosses the gap by magnetism, and the voltage on the far side is set by the turns. A control transformer is how a motor starter gets its own lower control voltage. See it: Wye and delta →

Loads

The things that use the current. A load is the only place on a drawing where the hot side and the return side meet.

Lamp / luminaire A circle with a cross: a light fixture as a load. On this site it is the thing that goes copper when the path is complete. Do not confuse it with the coil (plain circle) or the motor (circle with an M). See it: Single-pole switch wiring →
Motor A circle marked M: a rotating load. On a control drawing it sits on the power rung, fed through a contactor's contacts. See it: Contactor wiring diagram →
Resistor / heating element A zigzag: a load that turns current straight into heat. A baseboard heater, a range element, or any resistance in a calculation. In the series/parallel drill every "resistor" is one of these. See it: Series / parallel practice →
Relay / contactor coil A plain circle, usually lettered: the electromagnet that pulls a set of contacts. It is a load on the control circuit. The letter on the coil matches the letter on the contacts it moves. Find the K coil, then find every K contact. See it: Contactor wiring diagram →

Protection (overcurrent devices)

Devices that open the circuit when the current is wrong. What size they must be is a code question; what the mark means is not.

Fuse A rounded box with a line through it: a link that melts once and is replaced. Protects the conductor, not the load. See it: Hot, neutral, ground →
Circuit breaker A switch blade with a small hump: it opens by hand like a switch, and opens by itself on overcurrent. Resettable. Looks like a switch with a bump on the blade. The bump is what makes it a breaker. See it: Hot, neutral, ground →
Two-pole breaker Two breaker blades tied by a dashed link, so an overcurrent on either leg opens both. Used where both conductors to the load are live. See it: 240 V receptacle wiring →
Thermal overload element A run of humps in the motor's line: a heater that warms with the motor current and trips a contact in the control circuit when the motor pulls too much for too long. It does not open the motor line itself. It opens a small contact that drops the coil, and the contactor does the rest. See it: Motor start/stop station →

Conductors and junctions

Lines, dots, and the marks that say "these two touch" or "these two only cross".

Conductors joined A dot where lines meet: the conductors connect. Current can turn onto any line that shares the dot. The single most important mark on the page. Miss it and every drawing with two circuits reads wrong. See it: How to read a schematic →
Conductors crossing (not joined) Two lines cross with no dot: they pass each other on the page and do not touch. Some drawings hop one line over the other to say the same thing. See it: 3-way switch wiring diagram →
Terminal A small open circle on a line: a screw or terminal-strip point where a wire lands. A place, not a joint. On this site the terminals are filled dots. On a manufacturer's drawing they are usually open circles with a number beside them. See it: How to read a schematic →
Ground / earth Three shrinking bars: a connection to earth, for reference and for a fault path. It carries nothing until something goes wrong. See it: Hot, neutral, ground →
Junction box A square marked J: a box where conductors are spliced or pulled through. Nothing is switched or used inside it. See it: Switch loop wiring →
Ladder rails (L1, L2) Two vertical lines with the supply across them. Every horizontal rung between them is one control path, read left to right with the coil or load at the far right. A ladder diagram is a schematic stood on its side. Same rules: find the supply, follow the rung, stop at an open contact. See it: Motor start/stop station →

Controls and sensors

Switches that something other than a hand operates — a coil, the daylight, a body in the room, a temperature, a clock.

Normally open contact Two bars with a gap: open at rest, closed when its coil pulls in. Lettered to match the coil that drives it. Nothing flows through it until the coil is energised. The holding contact in a start/stop station is one of these. See it: Motor start/stop station →
Normally closed contact Two bars with a slash through them: closed at rest, and it opens when the coil pulls in. The slash means "closed until told otherwise". An overload trip contact is normally closed for exactly that reason. See it: Motor start/stop station →
Photocell A switch with light falling on it: the daylight throws the blade. It conducts in the dark and opens in the light. The arrows point at the blade — light coming in. The opposite of a hand switch: darkness turns it on. See it: Photocell wiring →
Occupancy sensor A switch under a lens: a body in the room throws the blade closed, and a timer opens it again once the room has been empty for a while. See it: Occupancy sensor wiring →
Thermostat A switch thrown by temperature. Drawn like a single-pole with a t° beside it; whether heat closes it or opens it depends on the job. On the contactor page the "control switch" feeding the coil is a thermostat as often as not. See it: Contactor wiring diagram →
Time-delay contact A contact with a small clock over it: it changes state a set time after its coil does, not at the same instant. The hold-off in an occupancy sensor is one of these in spirit — the room empties, then the clock runs, then the contact opens. See it: Occupancy sensor wiring →

Look-alikes: the pairs that get mixed up

Most symbol mistakes are not "I do not know that one" but "I read it as the other one". These are the pairs, and the one detail that tells them apart.

Conductors joined

Conductors crossing (not joined)

A dot means the two conductors connect. No dot, they only cross on the page. This is the one that matters most.
Interrupteur unipolaire

Circuit breaker

Both are a blade between two terminals. The hump on the blade is what makes it a breaker — it can open on its own.
Three-way switch (SPDT)

Interrupteur unipolaire

Count the terminals on the right. One means a single-pole. Two means a three-way, and the blade is never "off" — it is always on one of them.
Lamp / luminaire

Relay / contactor coil

A circle with a cross is a light. A plain lettered circle is a coil — it pulls contacts, it does not glow.
Normally open contact

Normally closed contact

Same two bars. The slash means normally closed: it carries current at rest and opens when the coil pulls in.
Pushbutton, normally open

Pushbutton, normally closed

Look at where the bar sits. Above the terminals: nothing flows until pressed — a Start. On the terminals: it flows until pressed — a Stop.

Which symbol is this?

Tap the name that matches the mark. The wrong answers are drawn from the same family on purpose — a three-way against a single-pole, a normally closed contact against a normally open one — so a streak here means you are reading the detail, not the shape. Every answer links back to a diagram that uses the mark. Do 10 gives you a scored set.

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Questions fréquentes

Are these the official symbols?

They are the common ones, drawn in this site's own style so they match the interactive diagrams. Drawing sets vary a little between offices and between countries, which is why a real set of drawings carries a legend on the first sheet. When the legend and your memory disagree, the legend wins — every time.

Why is part of each symbol copper?

Copper on this site always marks the part that moves or senses: the blade of a switch, the bar of a pushbutton, the joint where two conductors actually connect. It is a teaching cue, not a wire colour. On the live diagrams the same copper marks the energised path.

What is the difference between a schematic symbol and a plan symbol?

A schematic shows the electrical relationships — a switch is a blade, a lamp is a crossed circle, and the lines are conductors. A floor plan shows where things are — a receptacle is a circle at the wall, a switch is an S beside a door, and the lines are cable runs. The receptacles here are drawn the plan way because that is where you meet them; everything else is schematic.

Which ones should I learn first?

The single-pole switch, the lamp, the joined-versus-crossing dot, and the source. With those four you can read every lighting diagram on this site. Add the three-way, the coil and the two contact marks and you can read the motor control pages too.

Never read a schematic before? How to read a schematic builds one circuit from these marks one symbol at a time, then shows you how a control drawing stands them on their side. Then see them working together in the interactive wiring diagrams.

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