Wiring a three-prong plug incorrectly is a leading cause of equipment damage, nuisance GFCI tripping, and severe shock hazards. The correct three prong plug wiring color code depends entirely on your region's governing standard (NEMA for North America, BS 1363 for the UK, and CEE 7 / Schuko for the EU). Below is the definitive reference to get it right the first time, without the guesswork.
Master Three Prong Plug Wiring Color Code Table
Use this table as your primary bench reference. Always verify the physical plug type matches the standard before relying on the wire colors, as imported appliances frequently mix regional cord sets.
| Region / Standard | Prong / Pin Function | Symbol / Marking | Modern Wire Color | Legacy / Old Wire Color | Terminal Screw Color |
|---|---|---|---|---|---|
| US / Canada (NEMA 5-15P / 5-20P) |
Hot (Line) | L, X, or Brass | Black | Red (rare in cords) | Brass (Gold) |
| Neutral | N, W, or Silver | White | Gray | Silver | |
| Ground (Earth) | G, ⏚, or Green | Green / Bare Copper | N/A | Green | |
| UK (BS 1363) |
Live | L (Brown fuse side) | Brown | Red (Pre-1970s) | Brass (Right pin) |
| Neutral | N (Blue) | Blue | Black (Pre-1970s) | Silver (Left pin) | |
| Earth | E, ⏚ (Green/Yellow) | Green & Yellow Stripe | Green (Pre-1970s) | Top pin (Internal) | |
| EU / IEC (CEE 7/7 Schuko) |
Live (Line) | L | Brown (or Black) | Red / Black | Right Pin / Side Clip |
| Neutral | N | Blue (or Light Blue) | Blue / Gray | Left Pin / Side Clip | |
| Earth | PE, ⏚ | Green & Yellow Stripe | Green | Top/Bottom Earth Clips |
Rows People Get Wrong (And How to Avoid Them)
Even experienced makers stumble on these specific edge cases when rewiring plugs:
1. The "Black is Always Hot" Trap (Old UK vs. US)
If you are repairing a vintage UK appliance (pre-1970s) wired with a black and red cord, the black wire is the Neutral, and the red is Live. If you apply US logic (where black is always Hot) to an old British cord, you will reverse the polarity or short the circuit. Always treat old black UK flex as Neutral unless verified with a meter.
2. Ignoring the Polarized Blade (US NEMA 5-15P)
In North America, the NEMA 5-15P plug is polarized. The Neutral blade is physically wider (7.9mm) than the Hot blade (6.3mm). If you wire the Black (Hot) wire to the Silver screw (which connects to the wide blade), the plug won't fit into a standard polarized receptacle. If you force it by filing the blade or using an adapter, the appliance's internal switch will break the Neutral instead of the Hot, leaving internal components energized at 120V even when turned "off".
3. The Ground/Neutral Swap on 3-Wire Dryer/Range Cords
While this guide focuses on standard 15A/13A plugs, the same color logic applies to heavy 3-prong NEMA 10-30R dryer cords (Black, White, Red). In legacy 3-wire setups, the center White wire is the Neutral/Ground combined. Modern 4-wire setups (NEMA 14-30) separate them. Never bond Neutral to Ground on the appliance side of a 4-wire plug.
Safe Interpretation When Markings Are Faded or Missing
Cords left in hot attics or exposed to UV light often suffer from faded insulation where the white wire turns yellow, or the green wire turns brown. Never guess based on faded colors. Use this definitive multimeter continuity test to map the wires to the physical prongs:
- De-energize and Isolate: Ensure the cord is completely unplugged from the wall and disconnected from the appliance.
- Set Multimeter: Turn your multimeter to the Continuity setting (the diode/soundwave symbol).
- Identify the Ground Prong: On a US plug, this is the round U-shaped pin. On a UK plug, it's the top rectangular pin. Touch one probe to the ground pin and the other to the bare/green wire. You should hear a beep (read < 1 ohm).
- Identify the Neutral Prong: On a US plug, this is the wider flat blade. On a UK plug, it's the left-hand pin (with the plug facing you, pins pointing up). Test for continuity to the white/blue wire.
- Identify the Hot Prong: On a US plug, this is the narrower flat blade. On a UK plug, it's the right-hand pin (fused side). Test for continuity to the black/brown wire.
Decision Tree: Choosing Your Replacement Cord
Don't just grab any 3-wire cable from the bin. The jacket type and AWG must match the environment and the load. Use this decision matrix to select the exact cord specification you need.
| Condition (If...) | Then Choose... | Concrete Part / Spec to Buy |
|---|---|---|
| US region, standard indoor appliance, draw < 10A (e.g., lamp, radio) | 18 AWG SVT (Vacuum cleaner grade, indoor only) | 18/3 SVT Cord Set (Generic or Leviton) |
| US region, heavy tool, outdoor use, or draw 10A–15A (e.g., drill, space heater) | 14 AWG SJTOW (Oil & Water resistant jacket) | 14/3 SJTOW Cord (e.g., Leviton 001-9844 or Woods 2884) |
| UK region, standard domestic appliance < 700W | 0.75mm² flex with a 3A fused BS 1363 plug | MK Logic 13A Plug + 0.75mm² 3-core flex (Rewireable) |
| UK region, high-draw appliance > 700W (e.g., kettle, toaster) | 1.25mm² flex with a 13A fused BS 1363 plug | Tower 13A Fused Plug + 1.25mm² PVC flex |
| EU region, standard Class I appliance (requires earth) | 1.0mm² or 1.5mm² H05VV-F (harmonized PVC flex) | H05VV-F 3G1.5mm² Cord with molded Schuko plug |
The Default Pick: For 90% of US DIY replacement projects involving power tools, shop vacs, or heavy appliances, terminate your search here: Buy a 14 AWG 3-conductor SJTOW cord with a pre-molded NEMA 5-15P plug. The SJTOW jacket resists abrasion and moisture, and 14 AWG safely handles the full 15A branch circuit limit without excessive voltage drop over standard 6-foot lengths.
Regional Standard Application & Code Caveats
When wiring or replacing plugs, you are bound by the electrical code of your local jurisdiction. While the color codes above are standardized by international bodies, enforcement and specific installation rules vary.
- North America (NEC / CEC): The NFPA 70 (National Electrical Code) strictly mandates the use of Green or Bare for equipment grounding conductors (Article 250.119). White or Gray is reserved exclusively for grounded (neutral) conductors. You cannot re-identify a white wire as hot inside a flexible cord.
- UK (BS 7671): The IET Wiring Regulations require all flexible cords to follow the harmonized CENELEC colors (Brown/Blue/Green-Yellow). If you encounter an old appliance with Red/Black/Green wiring, you must either replace the entire cord or clearly sleeve and label the wires at the plug termination to prevent future shock hazards.
- EU & International (IEC 60446): The International Electrotechnical Commission standardizes the Brown/Blue/Green-Yellow scheme. For deeper reference on global harmonized cable types, consult the Electronics Notes wiring colour code guide.
Final Directive: Always match the wire color to the physical terminal screw color (Brass=Black/Brown, Silver=White/Blue, Green=Green/Yellow). If the cord insulation is cracked, the strain relief is missing, or the plug prongs show signs of arcing (black pitting), do not attempt a repair. Cut the cord off and replace the entire assembly. Your local Authority Having Jurisdiction (AHJ) has the final say on code compliance for hardwired or modified equipment.
