An ordinary extension cord uses alternating current (AC), so it does not have a “positive” wire in the direct-current sense. The conductors are called hot, neutral and, on a grounded cord, equipment ground. On many two-wire parallel cords, the ribbed or marked conductor is neutral and the smooth conductor is hot—but this is a common convention, not a guarantee for every cord. If a cord is damaged or its markings and plug do not give a clear match, do not guess: replace it or ask a qualified electrician.
What the wires in an extension cord are called
Household mains power is AC, whose direction of current flow alternates. “Positive” and “negative” are therefore not the right way to identify the conductors in an ordinary extension cord. Use these terms instead:
- Hot (line or ungrounded conductor): carries power from the source.
- Neutral (grounded conductor): provides the return path in the circuit. It is not interchangeable with equipment ground.
- Equipment ground: the protective conductor in a grounded, three-wire cord. It is associated with the grounding pin and is not a substitute for neutral.
How to identify conductors on a two-wire cord
Use the plug as a clue on a polarized cord
On a common North American polarized two-blade plug, the wider blade is neutral and the narrower blade is hot. Polarization is intended to preserve the conductors’ orientation through the cord. This is useful only when the plug is polarized and the cord’s conductor-to-blade mapping can be traced reliably; it is not a reason to open an energized cord or infer a connection from appearance alone. The CPSC guidance describes the importance of proper polarization and continuity.
Ribbed and smooth insulation is a common convention, not proof
In common two-conductor parallel cord, the ribbed or otherwise marked side is generally used as neutral, while the smooth side is generally hot. Treat this as a convention, not a universal rule: cord construction and markings can vary, and appearance alone does not prove which conductor connects to which plug blade. The official sources cited here establish correct polarity and continuity, but do not establish the ribbed/smooth convention for every extension-cord construction.
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If both sides look alike, the plug is nonpolarized, markings are unclear, or the observed markings do not line up with a clearly traceable polarized plug, stop rather than guessing. Replace the cord or have a qualified person assess it. Do not cut it open or energize it to identify a conductor.
What changes on a three-wire cord
A three-wire cord has hot, neutral and equipment ground. The ground conductor connects to the grounding pin and protective grounding contact; it is not neutral and must not be omitted or repurposed. OSHA’s construction guidance on flexible cords calls for three-wire extension cords for grounding tools and equipment in that workplace context. That requirement should not be generalized into a claim that every household extension cord must be three-wire; choose a cord suited to the equipment and its grounding requirements.
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When to stop using a cord
Do not use a cord with exposed conductors, worn or split insulation, loose connections, heat damage, or a missing grounding pin. Flexible cords are more exposed to physical damage than fixed wiring; damage can create shock, burn or fire hazards. Do not try to solve these problems by twisting wires together, making a quick splice, or cutting off a ground pin. The safer choice is to replace the cord or seek qualified electrical help. See OSHA’s flexible-cord safety guidance and ESFI’s extension-cord safety tips.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to choose a replacement cord
Choose for the actual appliance or tool and where the cord will be used. A cord’s length, conductor size and current rating affect whether it is suitable for a load; do not treat example gauge-and-amperage ranges as universal sizing rules. Follow the cord and equipment ratings, and when in doubt, ask a qualified electrician.
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- Location: Use a cord marked for indoor or outdoor use as appropriate. Keep cords out of water and snow.
- Load and length: Match the cord’s rating to the equipment, accounting for its length. Do not use a lower-rated cord than the appliance requires or overload a cord.
- Grounding: Use a grounded cord when the equipment requires a grounding connection. Never force a three-prong plug into a two-slot outlet or remove the ground pin.
- Safety approval: Look for approval by an independent testing laboratory, such as UL, Intertek or CSA.
- Temporary use: Extension cords are temporary wiring, not a permanent substitute for a properly placed outlet. Do not cover them in a way that prevents heat from escaping.
These selection and use precautions are consistent with ESFI’s extension-cord safety tips. A receptacle polarity tester can help check a wall outlet, but it does not establish the internal mapping of loose conductors in a cord.
Quick Recap
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