Wire color is an identification convention, not proof that a conductor is safe. In typical US premises wiring, white or gray is the grounded (neutral) conductor, green or green-and-yellow—or a bare conductor—is equipment grounding, and other colors such as black or red are used for ungrounded (hot) conductors. IEC-style European wiring commonly uses brown, black or gray for line conductors, blue for neutral and green-yellow for protective earth. The governing code, installation date and wiring context always control.
Turn off, lock out and verify a circuit with an appropriate tester before touching any conductor. OSHA requires determining whether parts are energized by inquiry, observation or instruments; never rely on insulation color alone.
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US wire colors: what each conductor usually means
OSHA requires grounded and equipment-grounding conductors to be identifiable and distinguishable. Its training material states: “The grounded conductor of a branch circuit shall be identified by a continuous white or natural gray color.” Equipment-grounding conductors are identified with green, green with yellow stripes, or are bare. Ungrounded conductors use other colors.
| Typical US color | Usual function | Important qualification |
|---|---|---|
| White or natural gray | Grounded (neutral) conductor | Required identification in the cited OSHA guidance; do not assume every old or altered installation follows it. |
| Green, green with yellow stripes, or bare | Equipment grounding conductor | Provides a fault-current path; it is not a normal current-carrying neutral. |
| Black, red and other non-white/non-gray colors | Ungrounded (hot) conductors | Common practice, not a universal permission to identify a conductor solely by color. Verify the circuit and local code. |
In a standard single-phase circuit, black is often the line conductor and red may be a second ungrounded conductor or a switched leg. Those are conventions within typical installations, not a substitute for testing. A white conductor can also be repurposed in some older or specialized wiring when it is properly reidentified; treat an unexpected marking or termination as a reason to stop and investigate.
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European and IEC-style colors
A technical guide summarizing IEC practice lists brown for a single-phase line, black and gray for additional phase conductors, blue for neutral and green-yellow for protective earth (PE). This is a regional convention rather than a guarantee for every European country, product or installation. Check the current national rules and the equipment documentation before working.
| IEC-style color | Usual function |
|---|---|
| Brown | Line (single-phase live) |
| Black or gray | Additional line/phase conductors |
| Blue | Neutral |
| Green-yellow | Protective earth |
Do not transplant a European color assumption into a US panel, or a US assumption into European equipment. Imported appliances, adapters and field modifications can create combinations that do not match the dominant local convention.
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Color depends on the wiring context
Premises wiring
Building cables and raceways generally follow the jurisdiction’s electrical code, but age, renovations and undocumented changes matter. Inspect terminations, labels and circuit behavior rather than accepting a color at face value.
Flexible cords and extension cords
Extension-cord safety involves more than color. CPSC guidance emphasizes polarization, conductor continuity, wire size, strain relief and suitable jacketing. A cord’s molded plug, blade arrangement and markings can be as important as the insulation colors inside it. Replace damaged cords instead of attempting an uncertain color-based repair.
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Equipment internals
Appliances, control panels and machinery may use manufacturer-specific harness colors, numbered wires, multi-pin connectors or printed labels. The service manual and wiring diagram govern. A green wire in one system does not make every green wire in another system a protective-earth conductor.
DC, low-voltage and communications systems
DC power, controls, solar installations, batteries and communications cabling can use different conventions, including polarity colors selected by the manufacturer or industry standard. Identify the system type and consult its diagram; do not apply AC premises rules automatically.
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Legacy or altered installations
Older work may predate current color rules, contain faded insulation or have been modified by multiple people. A conductor that looks neutral may be energized, and a missing or compromised grounding conductor can leave exposed metal hazardous. Stop when the observed wiring does not match the expected circuit.
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Color is only an initial clue. Use a safe work procedure and an appropriately rated instrument.
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- Identify the circuit. Use the panel schedule, drawings and observation to determine the likely source. Do not assume one breaker controls every conductor in a box; multiwire or interconnected circuits can share a neutral or have more than one source.
- De-energize. Open the disconnecting means, apply lockout/tagout where required and prevent re-energization. OSHA calls for de-energizing and grounding, guarding, or otherwise protecting workers from energized parts.
- Test the tester. Confirm the instrument operates on a known live source, then test the conductors and the relevant reference points, and recheck the instrument on the known source. Use equipment rated for the system and environment.
- Use proximity detection as a screening tool, not sole proof. A non-contact voltage tester can indicate the presence of AC voltage without contact and is among the types of electrical safety equipment OSHA lists. It may miss voltage, respond to induced voltage or behave unpredictably around shielding and crowded conductors; follow it with a contact measurement when the procedure and equipment permit.
- Proceed only after a verified zero-energy state. If readings are unexpected, intermittent or affected by backfeed, stop and have a qualified electrician trace every source.
When testing is not within your training, or the installation has multiple sources, damaged insulation, wet conditions or unidentified conductors, use a qualified electrical professional.
Quick Recap
Quick identification checklist
- Which country’s code and which edition applied when the wiring was installed?
- Is this premises wiring, a flexible cord, equipment internals, DC, or a communications system?
- Does the conductor’s color agree with its termination, labels and the circuit diagram?
- Could the circuit have a second supply, shared neutral, generator, inverter, battery or backfeed?
- Has the circuit been isolated, locked out and tested with an appropriate instrument?
Common mistakes to avoid
- “White always means safe.” A neutral can carry current and can become energized by a fault or incorrect connection.
- “Green always means earth everywhere.” Confirm the governing standard, especially inside equipment or on non-AC systems.
- “The breaker label is enough.” Labels can be wrong or incomplete; verify at the work location.
- “A non-contact tester proves zero voltage.” It is a useful detector, not a universal absence-of-voltage test.
- “A familiar color makes a repair acceptable.” Conductor size, insulation rating, polarity, continuity, strain relief and grounding must also meet the applicable code.
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