The capacitor testing symbol on a digital multimeter (DMM) dial is universally represented by two parallel vertical lines (-||-), a variation with one solid and one hollow line (⊣⊢), or the direct abbreviation CAP. This setting configures the meter to output a known AC or pulsed DC signal to measure capacitance in Farads (F). However, identifying the component you are testing on a schematic requires navigating two competing symbol standards: the international IEC 60617 and the North American IEEE/ANSI Y32.2.
Below is the complete reference for multimeter dial settings, schematic symbols, and physical component markings you will encounter at the bench.
Complete Capacitor Symbol & Testing Reference Table
| Symbol / Marking | Standard / Context | Meaning in Practice | Required Testing Action |
|---|---|---|---|
-||- or CAP |
DMM Dial | Capacitance measurement mode (Farads). | Discharge capacitor first. Connect probes; observe polarity if meter specifies. |
Ω or ))) |
DMM Dial | Resistance / Continuity mode. | Do not use for Farads. Only useful to check for dead shorts or open circuits. |
|| (Two straight lines) |
IEC 60617 Schematic | Non-polarized capacitor (ceramic, film). | Test in either direction. Polarity is irrelevant. |
|( (Straight + Curved) |
IEEE/ANSI Schematic | Polarized capacitor (electrolytic, tantalum). | Curved plate is Negative. Straight plate is Positive. |
|| with + sign |
IEC 60617 Schematic | Polarized capacitor. | The + indicates the positive anode. Both plates drawn straight. |
Physical Stripe with - |
Aluminum Electrolytic Body | Cathode (Negative) indicator. | Connect meter's black/COM probe to the striped lead. |
Physical Stripe or + |
Solid Tantalum Body | Anode (Positive) indicator. | Connect meter's red/VΩ probe to the striped lead. |
Regional & Standard Variants: IEC vs. IEEE/ANSI
When tracing a circuit to find the test points, the schematic symbol dictates how you interpret polarity. The confusion stems from two dominant drafting standards:
- IEC 60617 (International/European): The IEC standard draws all capacitors with two identical, straight parallel lines. To denote a polarized capacitor (like an aluminum electrolytic), the drafter adds a
+sign next to the positive terminal, or a-sign next to the negative. This is the standard used in most modern CAD software (like Altium or KiCad) when set to international libraries. - IEEE 315 / ANSI Y32.2 (North American): The ANSI standard uses a physical representation of early capacitor construction. The positive plate is drawn as a straight line, while the negative plate (representing the outer foil or electrolyte interface) is drawn as a curved line. Note: The curved line is always negative in ANSI.
+ sign on the curved side. Always verify physical board silkscreen polarity against the component's physical stripe before applying power or probing.
The "Rows People Get Wrong" & Faded Markings
Even experienced technicians misinterpret specific capacitor symbols and markings. Here are the most common bench errors and how to handle degraded components.
1. The Ohms Trap (Using the Wrong DMM Symbol)
A persistent myth is that you can "test" a capacitor using the Resistance (Ω) symbol on a multimeter. When you apply the probes, the resistance reading climbs from near zero to infinite (OL) as the meter's internal battery charges the capacitor. This does not measure capacitance. It only proves the capacitor isn't a dead short. To measure actual degradation, you must use the -||- capacitance symbol, or better yet, an ESR (Equivalent Series Resistance) meter. A 1000µF capacitor might read perfectly on a DMM's capacitance mode but fail under load due to high ESR, which a standard DMM cannot detect.
2. The Tantalum vs. Electrolytic Polarity Reversal
On physical aluminum electrolytic capacitors, the printed stripe with minus signs (-) indicates the negative cathode. However, on solid tantalum capacitors (the small epoxy-dipped teardrops), a printed stripe or a + mark indicates the positive anode. Reversing a tantalum capacitor during testing or soldering can cause it to short, overheat, and fail catastrophically. Always check the datasheet for vintage or unmarked tantalums.
3. Misreading the 3-Digit EIA Code
Ceramic disc and SMD capacitors use a 3-digit EIA code. A capacitor marked 104 is not 104 pF. The first two digits are the significant figures (10), and the third digit is the multiplier (number of zeros). Therefore, 104 = 100,000 pF, which converts to 100 nF or 0.1 µF. A mark of 223 is 22,000 pF (22 nF).
Safe Interpretation for Faded or Missing Markings
When a capacitor's epoxy sleeve has shrunk, cracked, or faded, leaving the µF and voltage ratings illegible, follow this protocol:
- Discharge Safely: Never short a faded capacitor with a screwdriver. Use a 100-ohm, 5W power resistor on insulated alligator clips to bleed off stored charge safely.
- Measure Physical Dimensions: Use digital calipers to measure the can diameter and length (e.g., 10mm x 16mm). Cross-reference this with standard radial can sizes. A 10x16mm can is typically 1000µF at 16V or 25V in modern switching power supplies.
- Use an LCR Meter: An LCR meter (like the DER EE DE-5000) applies an AC test signal (usually 1 kHz or 120 Hz) to measure the exact capacitance and dissipation factor, even if the physical ink is completely gone. According to All About Circuits, testing electrolytics at 120 Hz provides a more accurate real-world operating value than the standard 1 kHz used for ceramics.
Frequently Asked Questions
What is the exact capacitor testing symbol on a Fluke multimeter?
On industry-standard meters like the Fluke 87V, the capacitor testing symbol is a distinct -||- icon located on the rotary dial. On some compact Fluke models (like the 115 or 117), the capacitance function shares a dial position with the diode test or frequency. You must press the yellow function button to toggle the display from the diode symbol to the capacitance symbol before taking a reading.
Can I test a capacitor if my multimeter lacks the capacitance symbol?
If your DMM only has Voltage, Current, and Resistance symbols, you cannot measure the exact Farad rating. You can only use the Ω symbol to check for a dead short (a reading of 0.0 ohms that never changes). To actually measure capacitance without a CAP mode, you must build a simple 555-timer astable oscillator circuit where the capacitor under test dictates the output frequency, then measure the frequency with an oscilloscope or a frequency-counter app and calculate the capacitance using the 555 timing formula.
Why does the schematic capacitor symbol have an arrow through it?
A capacitor symbol with a diagonal arrow pointing through the plates (or intersecting them) represents a variable capacitor or a trimmer capacitor. These are typically small ceramic or air-dielectric components used in RF tuning circuits. When testing these, you must connect your multimeter's CAP probes, then use a non-metallic (plastic) tuning tool to adjust the screw while watching the multimeter display. The capacitance value should sweep smoothly across its rated range (e.g., 5 pF to 50 pF) without any sudden jumps or open-circuit dropouts, which would indicate damaged internal wiper contacts.
