A circuit symbol is a standardised shorthand for a component. In the UK, schools, exam boards and industry all use the same standard — BS EN 60617, the British version of the international IEC 60617. Learn to read three things from every symbol and diagrams stop being a memory test: what the component is, its key value or rating, and — the part most people skip — its polarity or orientation.
Most wiring mistakes don't come from forgetting what a resistor looks like. They come from ignoring polarity on cells, electrolytic capacitors, diodes and LEDs, and from mixing up the modern rectangular resistor symbol with the older zig-zag one still seen in US datasheets.
This guide covers the circuit symbols you'll meet across GCSE and A-level, plus the everyday ones hobbyists and technicians rely on. It explains what each represents to BS EN 60617, flags where orientation matters, and points to the right part if you need one. If you're building from a diagram rather than just reading it, our guide to breadboards covers turning a schematic into a working circuit.
What are circuit symbols, and why is there a standard?
A circuit symbol represents a component regardless of its physical size or make. A resistor is the same symbol whether it's a tiny surface-mount part or a large wirewound one — because a schematic describes how a circuit works, not how it's laid out. The value of a shared standard is simple: if everyone drew components their own way, a diagram would only be readable by its author. BS EN 60617 gives every engineer, teacher and student the same vocabulary, and it's the convention exam boards expect. Internationally it's identical to IEC 60617, so a diagram drawn in Britain reads the same across most of the world. The one exception you'll still meet is the older American (ANSI) style common in datasheets and hobby forums — the differences are small but real, and the resistor is the classic trap, covered below.
The common circuit symbols, and what each tells you
The table groups the symbols you'll use most often. The middle column is the useful part — what the symbol communicates beyond simply naming the component, including whether it has to go into the circuit a particular way round.
| Component |
What the BS EN 60617 symbol shows |
Orientation matters? |
| Cell / battery |
A long line (positive) and a short thick line (negative); a battery is several cells in series |
Yes — polarity |
| Resistor (fixed) |
A plain rectangle (US datasheets use a zig-zag — same component) |
No |
| Variable resistor / potentiometer |
A resistor with an arrow (variable) or a third tap arrow (potentiometer) |
Wiper terminal only |
| Capacitor |
Two parallel lines; a polarised (electrolytic) type adds a curved plate and a + mark |
Electrolytic: yes |
| Diode |
A triangle pointing to a bar; current flows the way the triangle points, the bar is the cathode |
Yes — polarity |
| LED |
A diode with two arrows pointing away (emitted light); same polarity rule |
Yes — polarity |
| Transistor (NPN / PNP) |
A circle with base, collector and emitter; the emitter arrow points out (NPN) or in (PNP) |
Yes — pinout |
| Switch (SPST) |
A break in the line with a hinged lever, drawn open |
No |
| Fuse |
A rectangle with a line through it, representing the fusible link |
No |
| Lamp |
A circle with a cross (indicator) or a loop (filament lamp) |
No |
| Motor |
A circle containing the letter M (a generator uses G) |
Direction depends on polarity |
If you're stocking up on the parts behind these symbols, the components range covers the lot — from resistors and capacitors to diodes and transistors and LEDs.
Why does the resistor symbol look different in some diagrams?
This is the single most common source of confusion, and it's worth understanding rather than memorising. Two conventions are in circulation. BS EN 60617 and IEC 60617 — used in UK education and across Europe — draw a fixed resistor as a plain rectangle. The older American standard draws it as a jagged zig-zag. They mean exactly the same thing. It trips people up because datasheets, tutorials and hobby projects are heavily US-influenced, so students learn the rectangle in class and then meet the zig-zag everywhere online. For coursework and exams, use the rectangle; when reading a datasheet, read the zig-zag as the same component.
How do you tell which way round a component goes?
Polarity is where reading a symbol becomes building a working circuit. Several components won't work — or will be damaged — if fitted the wrong way round, and the symbol tells you which. Cells and batteries have a positive long line; reverse the supply and nothing behaves. Electrolytic capacitors carry a + mark and can fail if fitted backwards, whereas non-polarised types have no such constraint. Diodes and LEDs conduct only in the direction the triangle points, so an LED fitted the wrong way simply won't light. Transistors have a defined pinout — base, collector and emitter are not interchangeable. A reliable habit is to mark every polarised component on the schematic and confirm its real-world orientation against the datasheet before building; it takes a minute and removes the most common reason a circuit doesn't work first time. The guide to fuses is a useful companion if your circuit includes protection.
Turning a schematic into a real circuit? Explore the full components range — resistors, capacitors, semiconductors and more.
Explore the components range
Common questions
What standard are UK circuit symbols based on?
UK circuit symbols follow BS EN 60617, the British adoption of the international IEC 60617. It's used in schools, by exam boards and across industry, so learning it once serves you from GCSE through professional engineering.
Why does the resistor symbol look different online?
Most online content is US-influenced and uses the older zig-zag resistor symbol, while UK and European standards use a plain rectangle. Both mean an identical component — use the rectangle for coursework and read the zig-zag as the same thing in datasheets.
Which components have to go in a particular way round?
Cells and batteries, electrolytic capacitors, diodes, LEDs and transistors are all orientation-sensitive. Their symbols indicate polarity — the long line on a cell, the + on an electrolytic capacitor, or the bar on a diode.
Are circuit symbols the same for GCSE and A-level?
Yes. Both use BS EN 60617, so the symbols learned at GCSE carry through to A-level and beyond. A-level introduces more components, such as operational amplifiers and logic gates, but the underlying standard doesn't change.
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