How to Wire an Extension Cord Plug

A worn or cracked plug at the end of an otherwise good extension cord is one of the few electrical repairs a careful DIYer can handle safely at home. If the cord body is in good shape and the damage is limited to the plug end -- a cracked shell, a loose prong, a scorched terminal, or a plug that has pulled apart from the cord -- replacing just the plug is a fast, inexpensive fix. All you need is a matching replacement plug, basic hand tools, and about fifteen minutes.

A new plug is not always the right fix, though. If the cord's outer jacket is frayed, cracked, or split anywhere along its length -- not just at the plug -- or you can see bare copper mid-cord, replace the entire cord instead of patching it with tape or a new end. This guide covers US-style NEMA plugs and UK BS 1363 plugs, walks through the wiring step by step, and gives you a wire gauge reference so a replacement plug or cord matches the actual load.

When to Replace the Plug vs. Replace the Whole Cord

Not every damaged cord needs a full replacement, but be honest about where the damage is and how deep it goes.

Replace just the plug when:

• The plastic housing is cracked, melted, or missing a piece, but the cord jacket right behind it is intact.
• A prong is bent, loose, or has broken off inside the shell.
• The plug shows discoloration or light scorching right at the terminals, but the cord itself tests fine.
• The cord has simply separated from the plug at the strain-relief point.

Replace the entire cord when:

• The outer jacket is frayed, cut, or cracked anywhere along the run, exposing colored inner insulation or bare wire.
• You see deep scorching, melted insulation, or a burn smell anywhere on the cord, not just at the plug.
• The cord has been pinched, run over, or crushed repeatedly (common under doors or furniture) -- internal strand damage is not always visible from outside.
• The cord is warm to the touch along its length during normal use, pointing to internal damage rather than a bad connection at the plug.

Never wrap damaged cord insulation in electrical tape as a permanent fix. Tape does not restore the wire's insulation rating, and a taped-over crack can still arc or overheat under load. If in doubt, replace the cord.

Safety First

Before you touch any wire, follow these rules without exception.

• Unplug the cord completely and keep it unplugged for the entire job. Never wire a plug while the cord is plugged in, even into an outlet you think is switched off, and never work on a plug within reach of a live outlet.
• Check the cord's full length for damage before you start, as described above. If damage extends beyond the plug end, replace the cord instead.
• Match the plug to the load. Use a replacement plug rated for at least the amperage and voltage of whatever you plan to run through it. A 15A plug on a 20A tool circuit is a fire risk, not a shortcut.
• Discard cords or plugs that show scorching, melting, or a burnt smell. These signal a fault that already happened once and is likely to happen again -- do not repair and reuse them.
• Work on a dry, well-lit surface, away from water, damp concrete, or outdoor conditions while you are wiring.
• When in doubt, stop. If you are not confident identifying hot, neutral, and ground, have a qualified electrician handle it.

Tools and Materials

You do not need a large kit for this job. Gather everything before you start.

Buy the replacement plug first and read its rating off the packaging. Extension cord jackets are usually printed with the wire gauge (for example "16 AWG" or "14/3") and sometimes an amperage rating -- match the new plug to that, not just to what fits the shell.

How to Wire a US NEMA 5-15 Grounded Plug (3-Prong)

The NEMA 5-15 is the standard US household plug: 15A, 125V, with two flat blades and a round ground pin, found on most household and light-duty extension cords.

Terminal identification:

• Brass (gold-colored) screw = hot. This connects to the narrower of the two flat blades.
• Silver screw = neutral. This connects to the wider flat blade.
• Green screw = ground. This connects to the round pin.

Wire color to terminal mapping:

• Black wire -> brass/hot terminal
• White wire -> silver/neutral terminal
• Green wire (or bare copper) -> green/ground terminal

Step-by-step:

1. Unplug the cord and cut off the damaged plug cleanly with wire cutters, leaving as much good cord as possible.
2. Unscrew and remove the plug housing, then slide it (open side toward the cut end) onto the cord before you strip anything -- it is easy to forget this and have to cut the wires back again.
3. Strip about 2 inches of the outer jacket to expose the three individual conductors, being careful not to nick their insulation.
4. Strip about 0.75 inch of insulation from the end of each conductor, exposing clean copper with no nicked or cut strands.
5. If the plug has a built-in strain-relief clamp, feed the wires through it now. If not, tie an Underwriters knot in the black and white conductors before connecting them -- the knot sits inside the shell and takes the pulling force so tension never reaches the screws.
6. Using needle-nose pliers, bend each stripped wire end into a small hook shaped to wrap clockwise around its terminal screw.
7. Hook the black wire clockwise around the brass (hot) screw, the white wire clockwise around the silver (neutral) screw, and the green or bare wire clockwise around the green (ground) screw. Clockwise matters: tightening the screw closes the loop tighter instead of springing it open.
8. Tighten each screw firmly, then give the wire a gentle tug to confirm it will not slip out.
9. Check that no bare copper is visible outside the terminal screws or the shell, then close the housing and tighten its assembly screws so the strain-relief clamp or knot sits fully inside.
10. Inspect the finished plug -- prongs straight, housing closed, no exposed wire -- before you plug it in for the first time.

How to Wire a 2-Prong (Non-Grounded, Polarized) Plug

Two-prong plugs show up on double-insulated power tools, lamps, and small appliances that do not require a ground path. They have no round pin, only two flat blades of different widths, a design called polarization.

• Wide blade = neutral (white wire)
• Narrow blade = hot (black wire)

Wiring a 2-prong plug follows the same process as the NEMA 5-15 above, minus the ground connection: strip the jacket and conductors, use the strain-relief clamp or an Underwriters knot, hook each wire clockwise onto its terminal, and tighten. The one thing to get right is matching wide-to-neutral and narrow-to-hot -- reversing them defeats the polarization the plug was designed to provide.

How to Wire a UK Plug (BS 1363, 3-Pin)

UK plugs follow the BS 1363 standard: three rectangular pins in a triangular layout, with a cartridge fuse built in.

Wire color mapping:

• Brown = live (L)
• Blue = neutral (N)
• Green/yellow = earth (E)

Pin positions, viewed from the front of the plug with the earth pin at the top:

• Top center = earth (E) -- this pin is longer than the other two, so it opens the shutters on a UK socket before the live and neutral pins make contact.
• Right = live (L)
• Left = neutral (N)

Step-by-step:

1. Unplug the appliance and remove the plug's cover screw, then lift off the cover to expose the terminals and fuse.
2. Strip roughly 2 inches of the outer sheath to expose the brown, blue, and green/yellow conductors, then strip about 0.75 inch of insulation from each conductor end.
3. Route the cord through the plug's cord grip (the built-in strain-relief clamp) before connecting any wires.
4. Connect brown to live (L), blue to neutral (N), and green/yellow to earth (E) at the top. Most modern BS 1363 plugs use screw-post or clamp-style terminals rather than a screw-and-hook design -- follow the specific plug's terminal style.
5. Fit or confirm the cartridge fuse. Use a 3A fuse for small appliances and lamps under roughly 700W, and a 13A fuse for higher-draw appliances like kettles, heaters, and irons. Do not default to 13A out of convenience -- the fuse protects the appliance's cord, and an oversized fuse will not blow before that cord overheats.
6. Tighten the cord grip so it clamps the outer sheath, not the individual colored wires.
7. Replace the cover and tighten the retaining screw.

UK plug wiring order and terminal layout have shifted slightly across older and newer BS 1363 revisions, and older or no-name plugs sometimes label terminals differently than current production. Match your work to a current BS 1363 reference or the instructions printed inside the specific plug you bought, not memory or an old diagram.

Wire Gauge and Extension Cord Length Reference

Extension cord wire gauge needs to match both the current draw of what you are plugging in and the length of the cord -- longer runs lose more voltage and generate more heat for a given gauge, so they need thicker wire (a lower AWG number) to stay safe. The figures below are general, commonly published guidance, not a substitute for the rating printed on your cord or device -- always confirm against those first.

Two rules when picking a replacement plug or cord:

• The cord's gauge must be equal to or thicker than what the device requires. If a tool's nameplate calls for 14 AWG minimum, a 16 AWG cord is undersized even if it is shorter than the table above suggests it can handle.
• The longer the run, the more voltage drop and heat for a given gauge. If extending a 14 AWG-rated tool's cord well past 100 ft, step up to 12 AWG.

Polarized vs. Grounded Plugs: Why the Rules Matter

Polarization and grounding are two different safety features that matter for different reasons.

Polarization is why the two blades on a plug are different widths. It guarantees that whichever prong plugs into the neutral slot of an outlet is always the same wire inside the device, so the device's internal switch consistently breaks the hot side of the circuit, not the neutral side. Never file down a wide neutral blade to force a polarized plug into an old, non-polarized outlet -- that defeats the purpose of the design and can leave a "switched off" device's internal wiring still live.

Grounding is a separate protection, present on 3-prong plugs. The ground pin gives fault current -- for example, current from a damaged internal wire touching a metal tool housing -- a safe path back to the panel instead of through whoever touches the tool. A grounded plug's round pin must never be removed, bent flat, or bypassed with an adapter that does not connect to a verified ground. Grounding is required by code on cords and equipment that are not double-insulated, which is why 2-prong plugs only appear on tools built with double insulation as a substitute protection.

Strain Relief: The Step Most People Skip

Strain relief keeps mechanical tension off the screw terminals inside the plug. Every time a cord is tugged, coiled, or pulled taut, that force needs somewhere to go besides the screws holding the wires in place.

A plug provides this in one of two ways: a built-in clamp that grips the cord's outer jacket as you tighten the housing, or -- when no clamp exists -- an Underwriters knot tied into the conductors before they reach the terminals. Either way, if someone yanks the cord, the pull stops at the clamp or knot, not at the screws.

Skipping strain relief is a common shortcut, and a bad one. Without it, repeated tugging loosens the terminal screws, a wire works free, and you get an exposed hot conductor inside the shell -- a setup for arcing, a short, or a fire. It takes an extra minute to tie the knot or seat the clamp; do not skip it.

Troubleshooting

Common Mistakes

• Reversing hot and neutral. Black on the silver terminal and white on the brass terminal defeats polarization and can leave internal switches breaking the wrong side of the circuit.
• Skipping the strain-relief knot or clamp. The single most common reason a plug fails months later, not immediately.
• Using a lighter-gauge cord than the tool requires. Check the tool's nameplate rating, not just what happens to be in the garage.
• Forcing a polarized or grounded plug into an incompatible outlet. Filing a blade or removing a ground pin removes the safety feature it exists to provide.
• Leaving stray strands of wire outside the terminal screw. A single loose copper strand touching an adjacent terminal or the metal shell is enough to cause a short.

Key Takeaways

• Replace just the plug when damage is limited to the plug end and the cord jacket is intact along its length; replace the whole cord if you find frayed or cracked insulation anywhere else.
• Always unplug the cord and keep it away from any live outlet before wiring a plug.
• US NEMA 5-15 plug: black to brass/hot, white to silver/neutral, green or bare copper to green/ground.
• 2-prong polarized plug: match the wide blade to neutral and the narrow blade to hot.
• UK BS 1363 plug: brown to live, blue to neutral, green/yellow to earth, with earth as the longer top-center pin -- and fit the correct fuse rating for the appliance, not a default 13A.
• Match the replacement plug and cord gauge to the amperage of the load, and upsize the gauge for longer runs.
• Always use the plug's built-in strain-relief clamp or tie an Underwriters knot so tension never pulls on the terminal screws.
• Never remove a ground pin or file down a polarized blade to force a fit.
• Inspect the finished plug for exposed bare wire before you plug it in.

Frequently asked questions

What color wires go where on a US extension cord plug?

On a standard NEMA 5-15 plug, the black (hot) wire connects to the brass or gold screw, the white (neutral) wire connects to the silver screw, and the green or bare copper (ground) wire connects to the green screw. The brass terminal feeds the narrow blade and the silver terminal feeds the wide blade.

How do you wire a UK 3-pin plug?

Connect the brown wire to the live (L) terminal on the right, the blue wire to the neutral (N) terminal on the left, and the green/yellow wire to the earth (E) terminal at the top, viewed from the front with earth up. Fit a cartridge fuse rated for the appliance, typically 3A for lamps or 13A for higher-draw items, then secure the cord grip before closing the cover.

Can I repair a cut extension cord myself?

You can safely replace a damaged plug if the cord jacket is intact along its full length. If the cut or fraying is mid-cord, or you see cracked insulation anywhere besides the plug end, replace the entire cord instead -- taping over cord damage does not restore its insulation rating and remains a fire risk.

What gauge wire do I need for a 15 amp extension cord?

14 AWG wire is commonly rated for up to about 15A on cords up to roughly 100 feet. Always confirm against the rating printed on the cord jacket or the device you are plugging in, and size up to 12 AWG for longer runs or higher-draw tools to limit voltage drop and heat.

Why do extension cord plugs need strain relief?

Strain relief -- either a built-in clamp or a tied Underwriters knot -- keeps pulling force off the terminal screws inside the plug. Without it, repeated tugging on the cord gradually loosens the screws until a wire pulls free, which can expose a live hot conductor inside the shell and create a shock or fire hazard.

What happens if you wire a plug with reversed hot and neutral wires?

Reversing hot and neutral defeats the plug's polarization, meaning a device's internal switch may end up breaking the neutral side of the circuit instead of the hot side. The device can still work, but the plug's internal wiring stays live even when the switch is off, which is a shock hazard during servicing.

Interactive diagrams for this guide

• Extension Cord Plug Wiring Diagram
• Extension Cord Wiring Diagram
• 3 Prong Plug Wiring Diagram
• Extension Cord Diagram
• 3 Prong Extension Cord Wiring Diagram
• 2 Prong Plug Wiring Diagram
• 110 Plug Wiring Diagram
• 110v Plug Wiring Diagram

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