In North America (NEC), standard extension cord internal wires are Black (Hot/Line), White (Neutral), and Green (Ground). In Europe and regions following IEC standards, the colors are Brown (Live), Blue (Neutral), and Green/Yellow (Earth). External jacket colors (yellow, orange) indicate duty cycle and visibility, not electrical function. If you are repairing a plug or splicing a cord, matching the correct internal conductor to the correct terminal is critical for preventing shocks and fires.
Extension Cord Internal Wire Color Code Reference Table
The following table maps the internal conductor colors to their electrical functions across major global standards. Always verify the standard printed on the cable jacket (e.g., UL, CE, SAA) before assuming the color code.
| Standard / Region | Line / Hot (Current Carrying) | Neutral (Return Path) | Ground / Earth (Safety Fault Path) | Typical Cable Markings |
|---|---|---|---|---|
| US / Canada (NEC / CEC) | Black | White (or Grey) | Green (or Green w/ Yellow Stripe) | SJTW, SVT, SJT |
| EU / International (IEC 60446) | Brown | Blue | Green / Yellow Stripe | H05VV-F, H07RN-F |
| Old UK (Pre-1970) | Red | Black | Green | Legacy PVC Flex |
| Australia / NZ (AS/NZS 3000) | Brown (Active) | Blue (Neutral) | Green / Yellow (Earth) | H05VV-F, TPS |
Decoding the Rows: What Each Color Means and Common Mistakes
Understanding the physical role of each conductor prevents dangerous miswiring. The Line/Hot wire carries the alternating current from the source to the load. The Neutral completes the circuit, carrying current back. The Ground/Earth carries zero current under normal conditions; it only exists to provide a low-resistance path to trip the breaker if a fault occurs.
Cheap, ungrounded 2-prong extension cords (SVT or SPT-2) only contain two wires: Black and White. In this configuration, White is the Neutral, not a ground. Never connect the white wire of a 2-prong cord to the green grounding screw of a 3-prong replacement plug. Doing so creates a severe shock hazard if the neutral bond fails upstream.
Rows People Get Wrong
- The 'Blue/Brown' Trap in North America: If you strip a cord in the US or Canada and find Brown and Blue wires, you are holding an imported IEC cord or a dangerously miswired hazard. Do not plug this into a standard 120V receptacle without verifying the internal wiring and plug configuration. IEC cords are often rated for 230V/250V systems.
- Old UK Red/Black Confusion: If you are working on vintage equipment in the UK, the old Black wire was Neutral. Modern IEC Black doesn't exist for mains flex, but DIYers often confuse old UK Black (Neutral) with US Black (Hot), resulting in reversed polarity.
- Faded Green/Yellow Stripes: In IEC and modern NEC cords, the ground wire is often solid green with a yellow spiral stripe. Over time, UV exposure and abrasion can wear the yellow stripe away, making it look like a solid green wire. It is still the ground.
External Jacket Colors and Letter Codes (SJTW vs SVT)
While internal wires follow strict electrical codes, the external jacket color of an extension cord is governed by industry convention and UL visibility guidelines rather than the NEC. Jacket colors tell you about the cord's intended environment, while the letter codes stamped into the rubber tell you its exact physical limits.
Jacket Color Conventions
- Yellow / Neon Green: High-visibility construction and jobsite cords. Designed to be seen by heavy equipment operators.
- Orange: Heavy-duty outdoor use. Often indicates a thicker gauge (12 AWG or 10 AWG) and a rugged, oil-resistant jacket.
- Black: Standard indoor/outdoor utility. Blends into landscaping; common in 14 AWG and 16 AWG.
- White / Beige: Indoor-only, lightweight cords (16 AWG or 18 AWG). Designed to hide against baseboards and walls. The PVC jacket will crack and fail rapidly if exposed to UV light.
- Red: Often used to denote specialized high-amperage cords, such as 30A/50A RV power cables or 240V appliance extensions.
Decoding the Letter Stamps
According to Cornell University Environmental Health and Safety, you should always check the letter code stamped on the jacket to verify the cord's rating. For an outdoor jobsite, you need an SJTW cord:
- S: Service grade (600V rating, though commonly used at 120V/240V).
- J: Junior (300V rating, thinner insulation, common in household cords).
- T: Thermoplastic jacket (vinyl/PVC).
- W: Weather/Water resistant (approved for outdoor use).
Safe Interpretation: Testing Faded or Non-Standard Wires
When an extension cord has been dragged across concrete, baked in the sun, or repaired previously with heat shrink, the internal wire colors may be faded, painted over, or entirely missing. Never guess the wiring based on position. The Consumer Product Safety Commission (CPSC) notes that miswired extension cords are a leading cause of residential electrical fires and tool-induced electrocution.
Set your digital multimeter (DMM) to the continuity setting (sound wave or diode symbol). With the cord completely unplugged, touch one probe to the narrow (Hot) blade of the male plug and the other probe to the stripped wire ends. A reading of < 1.0 Ω confirms that wire is the Hot conductor. Mark it with black electrical tape. Repeat for the wide blade (Neutral/White) and the round U-shaped pin (Ground/Green). If you read OL (Overload) on all wires, the cord has an internal break and must be discarded.
Decision Tree: Wiring a Replacement Plug on an Unknown Cord
When replacing a damaged male or female plug on an extension cord, use this decision path to terminate the wires correctly. This framework assumes you are working with a standard 3-prong, grounded 120V (NEMA 5-15) or 230V (Schuko/Type F) plug.
| Condition of Internal Wires | Action Required | Terminal Connection (NEMA 5-15) |
|---|---|---|
| Cord has clear Black, White, Green wires (NEC) | Wire directly to standard terminals. | Black → Brass screw White → Silver screw Green → Green screw |
| Cord has clear Brown, Blue, Green/Yellow wires (IEC) | Wire directly; ensure plug is rated for the cord's voltage. | Brown → Brass screw Blue → Silver screw Green/Yellow → Green screw |
| Cord has 3 wires, but colors are faded/unidentifiable | Perform DMM continuity test from the intact opposite end. | Map narrow blade wire → Brass Map wide blade wire → Silver Map round pin wire → Green |
| Cord has 3 wires, colors faded, AND opposite end is missing | Cut the cord and discard it. | Do not attempt to wire. The risk of reversed polarity or grounding a hot conductor is too high without a reference point. |
| Cord has only 2 wires (Black and White) | Install a 2-prong replacement plug only. | Black → Brass White → Silver (Leave Green screw empty) |
Always verify your work. After wiring the replacement plug and tightening the terminal screws to the manufacturer's torque specification (usually around 1.5 Nm for small brass screws), perform a final continuity check across the male blades to ensure no internal strands are bridging the hot and neutral terminals. A reading of OL (infinite resistance) between the brass and silver screws confirms a safe, open circuit ready for use.
