Barrel jack polarity (centre positive or centre negative)
Barrel jack polarity (centre positive or centre negative)
Which conductor of a barrel plug is positive: the inner pin or the outer sleeve.
What it looks like
A small circle with a dot in the middle, a C-shape around it, and plus and minus signs — the plus attached to whichever part is positive.
What it means
Read the symbol as a cross-section of the plug — the dot is the centre pin, the arc is the outer sleeve, and the sign next to each says its polarity. Centre positive is the common convention, but guitar pedals, some older audio gear and a scattering of routers use centre negative, and the plugs are physically identical. Connecting a supply of the wrong polarity destroys unprotected equipment instantly, and this symbol is the only thing on either device that warns you.
Defined by Manufacturer convention. Where a symbol differs between standards, the difference is described above rather than resolved — both versions are in circulation on real labels.
Other electrical and appliance symbols
| Symbol | Means |
|---|---|
| CE mark | The manufacturer declares the product meets the EU rules that apply to it. |
| UKCA mark | The manufacturer declares the product meets Great Britain's rules — the British counterpart to CE. |
| UL Listed | A complete product tested by Underwriters Laboratories against its safety standard. |
| UL Recognized Component | A component certified for use inside a larger product — not a certification of the finished item. |
| FCC mark | The device meets US limits on radio-frequency interference. |
| RoHS compliant | The product restricts ten hazardous substances, including lead, mercury, cadmium and four phthalates. |
| Crossed-out wheelie bin (WEEE) | Do not put this in household waste — take it to a separate collection for electrical items or batteries. |
| Crossed-out bin with Pb, Cd or Hg | A battery for separate collection which also contains lead, cadmium or mercury above the reporting threshold. |
| Double insulated (Class II) | The appliance is protected by two layers of insulation and needs no earth connection. |
| Protective earth (ground) | This terminal must be connected to the protective earth conductor. |
| IP rating (IP67, IPX4) | How well the enclosure keeps out solids and water. First digit solids 0–6, second digit water 0–9. |
| EU energy label (A to G) | How efficient the appliance is, on a scale from A to G, alongside consumption figures. |
| EnergyGuide label (US) | The estimated annual energy cost of this appliance in the US, and how it compares with the range for its class. |
| Alternating current (AC) | Alternating current. On a power supply it marks the mains input side. |
| Direct current (DC) | Direct current. On a power supply it marks the output side. |
Common questions
- What does the barrel jack polarity (centre positive or centre negative) symbol mean?
- Which conductor of a barrel plug is positive: the inner pin or the outer sleeve.
- What does it look like?
- A small circle with a dot in the middle, a C-shape around it, and plus and minus signs — the plus attached to whichever part is positive.
Related pages
- Direct current (DC) Direct current. On a power supply it marks the output side.
- Alternating current (AC) Alternating current. On a power supply it marks the mains input side.
- CE mark The manufacturer declares the product meets the EU rules that apply to it.
- UKCA mark The manufacturer declares the product meets Great Britain's rules — the British counterpart to CE.
- UL Listed A complete product tested by Underwriters Laboratories against its safety standard.
- UL Recognized Component A component certified for use inside a larger product — not a certification of the finished item.
- FCC mark The device meets US limits on radio-frequency interference.
- RoHS compliant The product restricts ten hazardous substances, including lead, mercury, cadmium and four phthalates.
- Crossed-out wheelie bin (WEEE) Do not put this in household waste — take it to a separate collection for electrical items or batteries.
- Crossed-out bin with Pb, Cd or Hg A battery for separate collection which also contains lead, cadmium or mercury above the reporting threshold.
- Double insulated (Class II) The appliance is protected by two layers of insulation and needs no earth connection.
- Protective earth (ground) This terminal must be connected to the protective earth conductor.
Sources
- Typical range compiled from manufacturer specifications — At One Place