For a typical battery or low-voltage DC lead, red is positive (+) and black is negative (−). But color is not universal proof: the correct meaning depends on the equipment and wiring standard. Check the +/− markings and product instructions first, and never apply the battery-lead convention to household AC wiring.
When red is positive and black is negative
In the familiar battery and battery-charger context, red identifies the positive connection and black the negative one. IEC 60335-2-29:2016 specifies red or “+” for positive and black or “−” for negative charger output, unless the design prevents an incorrect-polarity connection or determines polarity automatically. Its conductor-color text also associates red with the positive battery terminal and black with the negative terminal. IEC 60335-2-29:2016
For an actual connection, look for the molded, printed, or engraved + and − markings on the battery, device, or connector. Those markings and the equipment instructions are more useful than color alone when they disagree or the wiring history is unknown.
Why the same colors do not apply to every wire
A color has meaning within a particular standard and application; there is no single red-and-black rule for all electrical wiring. The International Electrotechnical Commission describes IEC 60445:2021 as providing general color and alphanumeric identification rules “with the aim of avoiding ambiguity and ensuring safe operation.” The IEC catalog also lists a 2026 consolidated version, so the 2021 edition is not the newest consolidated publication. IEC 60445:2021 catalog description IEC catalog listing
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The reproduced text of IEC 60445:2021 gives red for the positive DC line conductor and white for the negative DC line conductor. That differs from the red-positive, black-negative battery-charger convention above. Because this detail comes from a reproduction rather than the full normative text on the official catalog, treat it as an illustration of context-specific identification, not a universal wiring instruction. Reproduced IEC 60445:2021 text
Other applications vary too. A secondary summary of IEC 60204-1:2016 machinery wiring reports black for AC and DC power circuits and red for AC control circuits. A manufacturer’s discussion of European wiring describes brown and grey as possible positive and negative colors in an ungrounded two-wire DC configuration, with other assignments possible in grounded DC systems. Neither example establishes a general household wiring rule. IEC 60204-1:2016 summary Manufacturer support article on European wiring
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DC polarity is not the same question as AC wiring
A battery supplies direct current (DC), where the positive and negative terminals define polarity. Household mains is alternating current (AC), so it is not a positive-versus-negative battery connection. AC conductor colors and functions depend on the applicable system and installation rules. Do not use the red/black battery convention to identify household conductors or decide what is safe to touch.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to check an uncertain low-voltage DC connection
- Read the product markings. Find the + and − symbols at the battery terminals, device input, or connector.
- Check the equipment instructions. Follow the manufacturer’s connection diagram if colors and terminal markings appear inconsistent.
- Do not connect by color alone. If polarity is still uncertain, use an appropriate meter to verify the voltage and polarity on a known low-voltage DC circuit, or ask a qualified person.
- Stop if the wiring may be household mains. Do not probe energized mains wiring based on this guide; consult a qualified electrician.
A digital multimeter with a DC-voltage setting can be useful for identifying an unknown low-voltage DC lead, but the meter and procedure must be appropriate for the circuit. If you are not confident about the setup, leave the connection untouched and get qualified help.
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