Engineering Reference
Capacitor Voltage, Tolerance and Polarity Markings Reference
Lookup tables for capacitor voltage, tolerance, polarity and safety-class markings, with practical identification limits and datasheet verification rules.
Identification Boundary
Capacitor value, voltage, tolerance and polarity marks are separate information channels. Some are standardized commercial conventions; compact voltage codes, color details and production marks may be unique to a manufacturer series. Treat this page as a recognition aid, then verify the exact part number before design release.
Voltage Markings
| Marking | Likely meaning | Verification boundary |
|---|---|---|
| 6.3V / 6V3 | 6.3 V rated voltage | Printed voltage form; verify the series datasheet and derating requirement. |
| 10V / 10 | Often 10 V rated voltage | A bare number is not universal and can be a series-specific code. |
| 16V / 16 | Often 16 V rated voltage | Confirm that the number is a voltage mark rather than a date or lot code. |
| 25V / 25 | Often 25 V rated voltage | Use the manufacturer ordering code for production identification. |
| 50V / 50 | Often 50 V rated voltage | Small MLCCs may omit voltage information entirely. |
| 1H / 1A / 1C | Possible manufacturer voltage code | Letter-number voltage codes are series-specific; never decode them without the datasheet. |
Tolerance Suffixes
| Code | Tolerance | Context |
|---|---|---|
| B | ±0.1 pF | Absolute tolerance used for very small capacitance values. |
| C | ±0.25 pF | Absolute tolerance used for small ceramic capacitors. |
| D | ±0.5 pF | Absolute tolerance used for small capacitance values. |
| F | ±1% | Precision tolerance, often for stable dielectrics. |
| G | ±2% | Precision ceramic or film capacitor tolerance. |
| J | ±5% | Common capacitor tolerance marking. |
| K | ±10% | Very common ceramic capacitor tolerance marking. |
| M | ±20% | Common for ceramic, electrolytic, and tantalum capacitors. |
| Z | -20% / +80% | Wide tolerance marking often associated with high-K ceramics. |
Polarity Identification
| Family | Marking | Interpretation | Caution |
|---|---|---|---|
| Aluminum electrolytic | Stripe with minus signs | The stripe normally identifies the negative terminal. | Do not infer polarity from lead length after trimming. |
| Tantalum molded | Bar, plus sign, or beveled end | The marked end commonly identifies the positive terminal. | This convention is opposite the common aluminum-electrolytic stripe convention. |
| Radial LED-style lead cue | Longer lead | Some new through-hole polarized capacitors use a longer positive lead. | Lead length is unreliable on used or board-trimmed parts. |
| Nonpolar ceramic or film | No polarity mark | These parts normally have no required DC polarity. | A missing mark alone does not identify the dielectric or voltage rating. |
Mains Safety Classes
| Class | Connection | Purpose | Boundary |
|---|---|---|---|
| X1 / X2 | Across the line | Designed for line-to-line interference suppression under the applicable safety approval. | Use only parts carrying the required certification marks and rated mains category. |
| Y1 / Y2 | Line to protective earth or accessible secondary boundary | Designed for applications where failure could create an electric-shock hazard. | Do not substitute an ordinary capacitor or an X-only capacitor. |
Engineering Checks
- Keep working voltage below the rated voltage with application-appropriate derating.
- Check DC bias and temperature effects separately from printed tolerance.
- Never energize a polarized capacitor with reversed steady-state voltage.
- Measure salvaged parts, but do not use measurement as proof of voltage or safety rating.
Common Misreads
- Reading a lot code as a voltage rating.
- Treating K or M as a multiplier without considering suffix position.
- Applying the aluminum negative-stripe convention to molded tantalum.
- Substituting ordinary capacitors in X/Y safety positions.
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FAQ
Is a capacitor voltage code universal?
No. Explicit markings such as 25V are usually clear, but compact letter-number codes and bare numbers can be manufacturer- and series-specific.
What does K mean on a capacitor?
K commonly indicates ±10% capacitance tolerance. Confirm the suffix position and the manufacturer convention before treating it as a tolerance code.
What does M mean on a capacitor?
M commonly indicates ±20% capacitance tolerance.
Which side of an electrolytic capacitor is negative?
On common aluminum electrolytics, a stripe with minus signs normally identifies the negative terminal. Verify the package and datasheet.
Why is the stripe convention different on tantalum capacitors?
Molded tantalum capacitors commonly mark the positive terminal, so applying the aluminum-electrolytic convention can reverse the part.
Can an X2 capacitor replace a Y2 capacitor?
No. X and Y safety classes address different connection positions and failure hazards. Use the required approved class.
Do small ceramic capacitors show voltage rating?
Often they do not. The exact part number or packaging documentation is then required.
Can markings alone qualify a capacitor for production use?
No. Confirm capacitance, rated voltage, tolerance, dielectric, temperature range, safety approval, package and manufacturer series.