The potentiometers symbol designates a three-terminal variable resistor used for voltage division or current control. In North American schematics (IEEE/ANSI 315), it appears as a zig-zag resistor with a diagonal or perpendicular arrow. In European and international schematics (IEC 60617), it is drawn as an open rectangular box with an arrow pointing to the center. Regardless of the drawing style, the arrow always represents the wiper (the movable contact), while the two ends represent the fixed resistive track.
The Complete Potentiometer Symbol & Pinout Reference Table
Use this table to decode schematic symbols, physical pinouts, and silkscreen taper codes. When wiring physical components like a Bourns 3296W trimpot or an ALPS RK09K audio pot with the shaft facing you and pins pointing down, Pin 1 is left (CCW), Pin 2 is center (Wiper), and Pin 3 is right (CW).
| Symbol / Code | Standard / Type | Visual Description | Practical Meaning & Wiring |
|---|---|---|---|
| Potentiometer (US) | IEEE 315 / ANSI | Zig-zag line with an arrow pointing to the middle | 3-terminal voltage divider. Arrow is Wiper (Pin 2). |
| Potentiometer (EU) | IEC 60617 | Open rectangular box with an arrow pointing to the center | Identical function to IEEE. Standard in EU/UK schematics. |
| Rheostat | IEEE / IEC | Resistor symbol with arrow tied back to one end terminal | 2-terminal variable resistor for current limiting. Wiper tied to Pin 1 or 3. |
| Trimpot (Preset) | IEEE / IEC | Standard pot symbol with a line crossing the arrow shaft | Requires a tool to adjust. Used for calibration, not user control. |
| Taper Code 'B' | Physical Marking | Letter B stamped on casing (e.g., B10K) | Linear taper. 50% shaft rotation = 50% resistance. |
| Taper Code 'A' | Physical Marking | Letter A stamped on casing (e.g., A10K) | Audio/Logarithmic taper. Matches human hearing perception. |
| Taper Code 'C' | Physical Marking | Letter C stamped on casing (e.g., C10K) | Reverse Logarithmic taper. Used in specific synth/filter circuits. |
For a deeper look into how these symbols integrate into larger circuit diagrams, the All About Circuits standard symbols reference provides an excellent breakdown of passive component drafting rules.
Regional Standards & Rows People Get Wrong
While the underlying physics of a potentiometer never change, the way engineers draw them and manufacturers label them can trip up even experienced builders. Here is where the confusion usually happens on the bench.
IEEE 315 vs. IEC 60617: Which Applies to You?
If you are reading a schematic generated in the US, Canada, or Japan, you will almost exclusively see the IEEE 315 zig-zag symbol. If you are reading a schematic from Europe, the UK, or Australia, or using modern CAD software like KiCad set to IEC libraries, you will see the IEC 60617 rectangular box. Functionally, they are identical. Do not let the rectangular box trick you into thinking it represents a capacitor or an inductor; the arrow is the dead giveaway for a variable resistor.
The 'Rows People Get Wrong' Notes
- The Wiper Trap: Beginners often connect the load to Pin 1 or Pin 3, treating the pot as a fixed resistor with a movable tap. The arrow in the symbol always points to the wiper (Pin 2). The output voltage must always be taken from the wiper relative to ground.
- The Rheostat Confusion: If the schematic shows the arrow looping back and connecting to one of the outer terminals, it is a rheostat (2-terminal). If you wire a physical 3-pin pot this way, you must physically jumper Pin 2 to Pin 1 or Pin 3. If you leave the unused outer pin floating, wiper contact bounce will cause open-circuit dropouts when you turn the shaft.
- The Taper Swap (Asian vs. Western): Modern global manufacturers like Bourns and TT Electronics follow the standard: A = Logarithmic (Audio), B = Linear. However, some legacy and cheap unbranded Asian imports reverse this, marking Linear as 'A' and Log as 'B'. Always verify taper with a multimeter before soldering into an audio signal path.
Safe Interpretation When Markings Are Faded or Missing
When salvaging parts or repairing vintage gear, you will frequently encounter pots where the silkscreen taper code and resistance value have rubbed off. Here is the exact 4-step multimeter procedure to identify the pins and taper safely.
- Find the Total Resistance (Pins 1 & 3): Set your DMM to the Ohms range. Place probes on the two outer pins. Turn the shaft from end to end. The reading should remain stable at the nominal value (e.g., 10kΩ). If it fluctuates wildly, the resistive track is worn out—discard the pot.
- Identify the Wiper (Pin 2): Keep one probe on an outer pin and move the second probe to the center pin. Sweep the shaft. The resistance should smoothly transition from 0Ω to the total nominal value. This confirms the center pin is the wiper.
- Determine the Taper: Set the shaft exactly to the physical 50% mark (use the center detent if it has one, or eyeball the flat on a D-shaft). Measure between Pin 1 and Pin 2.
- If the reading is roughly 50% of the total resistance, it is Linear (B).
- If the reading is roughly 10% to 15% of the total resistance, it is Audio/Logarithmic (A).
- Check for Switches: Many audio pots (like the ALPS RK09K series) include a built-in SPST switch for power. If your pot has 5 pins instead of 3, the two extra pins are the switch contacts. Set your DMM to continuity, toggle the shaft click, and verify which pins close the circuit.
For official pinout diagrams and mechanical tolerances on modern replacement parts, the Bourns potentiometer catalog is the industry benchmark for verifying physical footprints against schematic symbols.
Frequently Asked Questions
What does the arrow mean on a potentiometers symbol?
The arrow on a potentiometers symbol represents the wiper, which is the movable contact that slides along the fixed resistive track. In a physical component, this corresponds to the center pin (Pin 2) on standard 3-pin layouts. The arrow's position in the drawing does not indicate the current physical position of the knob; it simply identifies which terminal provides the variable output voltage.
How do you wire a potentiometers symbol as a variable resistor?
To use a potentiometer as a 2-terminal variable resistor (rheostat) rather than a 3-terminal voltage divider, you connect your circuit to the wiper (the arrow terminal) and one of the outer terminals. The third outer terminal is left unconnected or, preferably, jumpered directly to the wiper pin. This jumper ensures that if the wiper momentarily loses contact with the resistive track due to dirt or vibration, the circuit defaults to the maximum resistance rather than going open-circuit.
Why are there two different schematic symbols for a potentiometer?
The two symbols exist because of different historical drafting standards. The IEEE 315 standard (dominant in North America) uses a zig-zag line to represent resistance, so a potentiometer is drawn as a zig-zag with an arrow. The IEC 60617 standard (dominant in Europe and international CAD libraries) uses a simple open rectangle to represent resistance, so the symbol is a rectangle with an arrow. Both mean the exact same thing electrically.
What is the difference between a trimpot symbol and a standard potentiometers symbol?
A trimpot (trimmer potentiometer) symbol looks identical to a standard potentiometer symbol, but it features an additional line drawn perpendicular to the arrow shaft, or the arrow is drawn with a T-bar instead of a standard point. This visual modifier indicates that the component is a 'preset'—meaning it is meant to be adjusted with a small screwdriver during factory calibration or bench setup, rather than by a user turning a knob on the front panel.
