3-Prong Extension Cord Wiring Diagram

3-Prong Extension Cord Wiring Diagram — interactive diagram. Open it in the editor to customise components and wiring.

This is a free printable 3 prong extension cord wiring diagram: download the diagram as SVG or open it and print to paper or PDF.

Wire a 3-prong extension cord correctly by connecting line, neutral, and earth conductors to the right terminals in both the plug and socket, ensuring safe and polarity-correct operation.

A 3-prong extension cord carries three conductors: line (also called live or hot), neutral, and earth (also called ground). The third prong — the earth/ground pin — is the critical safety addition over a 2-prong cord. It provides a low-resistance return path for fault current if a connected appliance develops an internal fault that puts voltage on its metal chassis. This path allows sufficient current to flow to trip the circuit breaker or blow the fuse, rather than leaving the chassis energised and presenting a shock hazard to anyone who touches it.

In most international plugs and sockets (IEC 60083, IEC 60884, BS 1363, NEMA 5-15), the conductors follow colour coding conventions. In North America (NEMA standards), the line (hot) conductor is black, neutral is white, and earth is green or bare copper. In IEC/European harmonised wiring (used in most international markets), the line is brown, neutral is blue, and earth is green/yellow striped. Always verify the colour coding against the relevant national standard before terminating — wire colours do not guarantee conductor identity.

The plug body contains three terminals corresponding to the three pins. The earth (ground) terminal connects to the largest or differently shaped pin — designed to mate first and disconnect last to ensure earth connection is always present when line and neutral are connected. The line and neutral pins are designed to prevent incorrect insertion in some plug standards (e.g., the neutral slot is wider in NEMA 5-15 to enforce polarity).

The socket (female) end of the extension cord mirrors the plug — the same three terminals, same conductor assignments. Line from the plug feeds to the line terminal of the socket, neutral to neutral, earth to earth.

Extension cords must be rated for the current they will carry. The cord's current capacity depends on conductor cross-section and length. Longer cords have higher resistance and will cause greater voltage drop under load, as well as generating more heat. Never coil an extension cord under load — a coiled energised cord generates heat that cannot dissipate, risks overheating the insulation, and is a fire hazard.

How to wire 3 prong extension cord wiring diagram

Identify conductor colours and verify with a continuity tester Examine the cord and identify the conductor colour coding. Do not assume — use a continuity tester or multimeter to verify which conductor runs through to which pin on the plug end before making any connections. In North America: black = line, white = neutral, green or bare = earth. In IEC harmonised: brown = line, blue = neutral, green/yellow = earth.
Prepare cable ends Strip the outer jacket back 40–50 mm from each end. Take care not to nick the insulation of the inner conductors. Strip each inner conductor 6–8 mm at the termination end. If the plug or socket uses screw terminals rather than crimp contacts, twist the stranded wires tightly and consider tinning them with solder to prevent strand separation in the terminal.
Wire the plug (male) end Open the plug body. Identify the earth terminal (usually the largest, or marked with the earth symbol or the letter E or G). Connect the earth conductor to the earth terminal. Connect the line conductor to the line terminal (marked L, or the smaller blade in NEMA plugs). Connect the neutral to the neutral terminal (marked N, or the larger blade slot side in NEMA). Tighten each screw firmly.
Engage the cable clamp in the plug body Before closing the plug body, seat the cable firmly in the strain relief or cord clamp. The clamp must grip the outer jacket — not the individual conductors — to ensure no pull force is transmitted to the terminal connections. Tighten the clamp screws so the cord cannot be pulled out with moderate force.
Wire the socket (female) end Open the socket body. Connect line to line, neutral to neutral, earth to earth — maintaining the same assignments throughout the full length of the cord. The earth contact in the socket is the pin that engages the earth prong of any plug inserted into it, and must have solid earth continuity back to the plug earth prong via the earth conductor.
Close all bodies and test before use Close and reassemble the plug and socket bodies, ensuring no conductors are pinched and no bare copper is exposed outside the terminals. Using a socket tester or multimeter, verify correct polarity (line to line, neutral to neutral), earth continuity, and absence of any line-to-earth or neutral-to-earth leakage.

Specifications

Conductors	3: Line (L), Neutral (N), Earth/Ground (E or G)
North American conductor colour code (NEMA)	Black = Line, White = Neutral, Green or Bare = Earth
IEC harmonised conductor colour code	Brown = Line, Blue = Neutral, Green/Yellow = Earth
Common current ratings	10 A, 13 A (UK), 15 A (North America), 16 A (IEC), 20 A
Minimum conductor cross-section (IEC, 16 A)	1.5 mm² per conductor
Minimum conductor gauge (NEMA, 15 A)	14 AWG
Earth pin function	Connects to appliance chassis; provides fault current return path; should make first and break last

Safety warnings

Never use a 3-prong-to-2-prong adapter (cheater plug) to defeat the earth pin. Removing the earth connection eliminates the shock protection that the third prong provides. If an appliance has a fault, the chassis will become live and present a lethal shock hazard with no earth path to trip the breaker.
Do not use an extension cord as a permanent wiring solution. Extension cords are designed for temporary connection of portable appliances. Using an extension cord as a substitute for a fixed socket outlet is a fire and safety hazard, is against electrical codes in most jurisdictions, and voids equipment warranties.
Never run extension cords under rugs, carpets, or through walls. Cords under coverings cannot dissipate heat and the covering masks damage. Cords run through walls or floors must meet fixed wiring requirements — they are no longer extension cords at that point.
Verify that the extension cord's current rating equals or exceeds the total current drawn by all devices connected to it. Overloaded extension cords overheat, melt insulation, and cause fires — often in areas where they are not visible. Use the correct gauge cord for the load.
Inspect extension cords before every use. Damaged insulation, cracked plug bodies, bent pins, and pulled-back wires at the plug are all hazards that require cord replacement, not temporary use. A damaged cord used near wet surfaces or in outdoor conditions can be fatal.

Tools needed

Wire strippers sized for the cord's conductor cross-section
Flat-blade screwdriver (for terminal screws in plug and socket body)
Multimeter or socket tester (to verify polarity and earth continuity after wiring)
Continuity tester or multimeter with continuity function
Soldering iron and electrical solder (optional, for tinning stranded conductors)
Electrician's tape or heat-shrink tubing (for any remedial insulation work)

Common mistakes

Swapping line and neutral at the socket end while correct at the plug: This creates reverse polarity at the socket — appliances plugged into the socket will be reverse-polarity even though the plug is correct. The polarity must be consistent from plug to socket throughout the entire cord length.
Connecting earth to a terminal other than the earth terminal: Wiring earth to the line or neutral terminal will either blow the fuse immediately (earth to line) or create a shock hazard on the neutral (earth to neutral). Always verify terminal identity before connecting.
Gripping individual conductor insulation with the cord clamp instead of the outer jacket: The clamp must hold the outer jacket. If only the inner insulation is gripped, any pull on the cord will stress the terminal connections, eventually pulling conductors out of terminals and creating a contact fault.
Using a cord with an inappropriate jacket for the application: An indoor-only jacket (smooth white or grey PVC) used outdoors will crack in UV and cold temperatures, exposing conductors. Always use a cord marked as suitable for the intended environment.
Coiling an extension cord under load: A coiled energised cord builds up heat in proportion to the current flowing. This can overheat and melt the insulation even when the cord is within its rated ampacity. Uncoil fully before use under any significant load.

Troubleshooting

Socket tester shows reverse polarity at extension cord socket: Cause: Line and neutral conductors are swapped at one or both ends of the cord — either internally in the cord, or crossed at the plug/socket terminal connections Fix: Open the plug and socket bodies and verify that the conductor connected to the line terminal at the plug is also connected to the line terminal at the socket. Use a continuity tester to trace each conductor end-to-end before re-terminating.
Appliance connected to extension cord trips the breaker under load but not at direct socket: Cause: Extension cord undersized for the load current, causing voltage drop and increased resistance that pushes current above the breaker trip threshold; or a high-resistance connection in the cord adding to total circuit impedance Fix: Check the cord's current rating against the appliance load. Measure voltage at the cord socket under load — if significantly below supply voltage, upgrade to a larger gauge cord. Inspect all terminal connections for tightness and signs of heat or arcing.
Extension cord plug or socket feels hot during use: Cause: High-resistance connection at a terminal screw, or the cord is overloaded beyond its current rating Fix: Disconnect immediately. A hot connector is a fire risk. Inspect the terminal connections inside the plug or socket — look for discolouration (yellowing of insulation, darkening of terminals) indicating past overheating. Re-terminate any loose or damaged connections, or replace the plug/socket and verify the cord is rated for the actual load current.

Frequently asked questions

What are the 3 wires in a 3-prong extension cord?

The three conductors are line (live/hot), neutral, and earth (ground). Line carries the supply voltage to the connected appliance. Neutral completes the return circuit. Earth is a safety conductor connected to the appliance chassis, designed to carry fault current and trip the breaker if an internal fault occurs — it carries no current in normal operation.

Does it matter which wire goes to which terminal in an extension cord?

Yes, absolutely. Reversing line and neutral (swapping hot and neutral) produces a condition called reverse polarity — the appliance chassis or switch contacts may be energised to line voltage even when the appliance is switched off. This is a shock hazard. Earth must connect only to the earth terminal — connecting earth to line or neutral is extremely dangerous.

What wire gauge should an extension cord use?

Wire gauge (AWG in North America, mm² elsewhere) must match the current rating required. In North America: 16 AWG for up to 13 A, 14 AWG for up to 15 A, 12 AWG for up to 20 A. In IEC systems: 1 mm² for up to 10 A, 1.5 mm² for up to 16 A, 2.5 mm² for up to 25 A. For longer cords, upsize the conductor to limit voltage drop.

Is it safe to repair a damaged extension cord by splicing it?

Splicing an extension cord with a connector or by twisting and taping wires together is generally not recommended for permanent or heavy-duty use. Any splice is a potential failure point — a source of increased resistance, heat, and arcing. In most jurisdictions, a repaired cord for workplace use must use a proper approved connector, not a taped splice. For safety, replace a damaged extension cord entirely.

Can I use a 3-prong extension cord outdoors?

Only if the cord is rated and marked for outdoor use. Outdoor-rated cords have a jacket material (typically thermoplastic rubber or flexible PVC compound) that resists UV, moisture, and low temperatures. Using an indoor-rated cord outdoors causes the jacket to crack, exposing conductors. The plug and socket of an outdoor cord should also be weatherproof, or protected by a cover when the socket is not in use.