Extension Cord Wiring Diagram

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

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

Correctly identify the active, neutral, and earth conductors in a mains extension cord and understand how connector polarity, conductor sizing, and protective earth bonding interact before you make or repair one.

An extension cord is deceptively simple in appearance but carries mains voltage, and a wiring error can create an electrocution hazard, a fire risk, or — critically — an unprotected earth that leaves equipment chassis live without tripping any overcurrent device. Understanding the diagram before you connect anything is not optional.

A correctly wired three-core extension cord contains: active (live), neutral, and earth (protective earth, PE). Wire colours follow regional standards. In Australia and the UK (and much of Europe under IEC 60446), the convention is brown = active, blue = neutral, green/yellow stripe = earth. In North America (NEC), black = hot, white = neutral, green or bare = ground. Never mix conventions in a single installation — this is a common source of miswiring when repairing imported equipment.

The plug end (male pins) connects incoming mains power. The socket end (female, with recessed contacts) connects the load. Polarity matters: the active conductor must connect to the active pin in both the plug and the socket. On Australian plugs the flat pins are active and neutral; the round pin is earth. On UK BS 1363 plugs, the rectangular pins carry active (right), neutral (left), and earth (top, larger). North American NEMA 5-15 uses narrow blade (hot), wide blade (neutral), and round prong (ground).

Conductor cross-section determines the safe current capacity (ampacity) of the cord. A 0.75 mm² core is suitable for light loads only (up to approximately 6 A). A 1.0 mm² core handles up to approximately 10 A. A 1.5 mm² core handles up to approximately 16 A (the standard domestic socket rating in many countries). For power tools and appliances drawing above 10 A, use 1.5 mm² or larger and keep total cord length under 30 m to avoid excessive voltage drop. Voltage drop above 5% of nominal will cause motor overheating and premature failure.

The earth conductor must be connected at both ends and must not be the current-carrying path during normal operation. Its sole purpose is to carry fault current to earth if the appliance casing becomes live, tripping the circuit breaker or RCD before a dangerous shock potential develops.

How to wire extension cord diagram

Select the correct cable and components Choose a flexible three-core cable rated for your load current and appropriate for the mechanical environment — H05VV-F or equivalent for indoor light use; H07RN-F rubber-sheathed cable for outdoor, construction, or workshop use. Select plug and socket bodies rated for the same or higher current than the cable.
Prepare the cable ends Cut the cable to the required length with a clean square cut. Strip the outer sheath back 40–50 mm using a cable stripper — do not score the inner conductor insulation. Strip 8 mm of insulation from each conductor end. Twist stranded conductors clockwise to prevent strand splaying.
Identify and connect the plug end (male) Open the plug body. Insert the cable through the cable clamp (gland) before making connections. Connect the earth conductor first (green/yellow or green): secure it to the earth terminal, which is longer and positioned at the top. Connect neutral (blue or white) and active (brown or black) to their marked terminals. Tighten terminals firmly to eliminate strand pullout risk.
Clamp the cable at the plug Tighten the cable clamp/cord grip so it grips the outer sheath firmly — pulling the cable should put strain on the sheath, not on the conductors inside. Exposed copper should not be visible beyond the terminal. Reassemble and tighten the plug body screws.
Connect the socket end (female) Open the socket body. Pass the cable through the cord grip. Connect earth, neutral, and active to their corresponding terminals — socket terminals are marked with symbols or letters (E/PE, N, L/A). Confirm polarity matches the plug end: active at plug active pin connects to active at socket active terminal. Clamp and reassemble.
Test before use Use a plug/socket polarity tester (available at hardware stores) to verify: correct polarity, earth present, and no live-neutral reversal. A multimeter continuity test from plug active pin to socket active contact, and from plug earth pin to socket earth contact, will confirm correct wiring before mains connection.

Specifications

Conductor colour — active (live)	Brown (IEC/AU/UK) or Black (North America NEC)
Conductor colour — neutral	Blue (IEC/AU/UK) or White (North America NEC)
Conductor colour — earth (PE)	Green/yellow stripe (IEC/AU/UK) or Green or bare (North America)
Cable type — indoor use	H05VV-F (IEC) or equivalent flexible PVC
Cable type — outdoor/industrial	H07RN-F rubber-sheathed flexible
1.5 mm² conductor ampacity (typical)	Up to 16 A (IEC/AS/NZS), 15 A (NEC)
Maximum recommended cord length at 15 A	30 m (1.5 mm²); increase conductor size for longer runs
Earth conductor must be	Longest conductor inside plug body — last to pull free under cord tension

Safety warnings

Electrical work on mains-voltage equipment must comply with applicable national standards: NEC/NFPA 70 (USA), BS 7671 (UK), AS/NZS 3000 (Australia/NZ), IEC 60364 (international). In many jurisdictions, permanent mains wiring must be performed or inspected by a licensed electrician.
Always verify that power is isolated and test with an approved voltage tester before working on any conductor — an unplugged cord may still be energised if the socket outlet behind it has not been isolated.
Never omit the protective earth conductor from an extension cord used with Class I (earthed) appliances. An earth-free cord on a Class I appliance creates an undetectable shock hazard.
Do not use an extension cord as a permanent wiring substitute. Extension cords are for temporary use only; permanent loads must be connected via fixed wiring to the correct circuit.
Do not exceed the current rating of the cable, plug, or socket — the lowest-rated component in the assembly is the limiting factor. Overloaded cords overheat inside insulation and can cause fires even when wound on a cord reel.

Tools needed

Cable stripper / insulation stripper
Screwdrivers (flathead for terminals, Phillips for body screws)
Multimeter (continuity and resistance measurement)
Plug/socket polarity tester
Wire cutters / side cutters
Permanent marker (for labelling if multiple cords)

Common mistakes

Reversing active and neutral connections at one end of the cord, creating a reverse-polarity hazard detectable only with a polarity tester.
Connecting the earth conductor too short inside the plug body so that if the cord is pulled, the earth terminal detaches before the current-carrying conductors — the earth must be the last conductor to pull free.
Using cable rated for indoor use (H05VV-F) in outdoor or workshop environments where it will be subject to oil, abrasion, or UV — the insulation degrades rapidly and becomes a shock hazard.
Rolling a fully loaded extension cord on a drum or reel — current through a coiled cord causes inductive heating that can melt insulation even when the cable is nominally within its rated current capacity.
Using tape-insulated butt-splice joins inside the plug or socket body rather than proper screw terminals, which vibrate loose and create arcing hazards.

Troubleshooting

Appliance does not power on when plugged into cord: Cause: Loose terminal connection, open-circuit conductor, or blown fuse in plug (where applicable) Fix: Test socket outlet independently. Use a multimeter to measure continuity from plug active pin to socket active terminal with cord unplugged. Inspect all terminal screws for tightness. Check plug fuse (BS 1363 plugs carry a cartridge fuse) if no continuity found.
Polarity tester shows reverse polarity at socket end: Cause: Active and neutral conductors swapped at the socket or plug terminal Fix: Isolate the cord (unplug from wall). Open the socket body. Verify active (brown/black) connects to the active terminal (marked L or A) and neutral (blue/white) to the neutral terminal (marked N). Swap if incorrect, retest.
Cord becomes hot during normal use: Cause: Load current exceeding cable ampacity, or cord wound on a reel while loaded Fix: Measure the load current with a clamp meter and compare to the cable's rated ampacity. Fully unwind the cord before use. If the current is within rating and the cord is uncoiled, the cable is faulty (damaged insulation creating partial fault) — replace the cord.

Frequently asked questions

Does polarity matter in an extension cord?

Yes, critically. The active (live) conductor must connect to the active pin at both ends. On a two-prong ungrounded cord, reversed polarity leaves an appliance's internal fuse on the neutral side rather than the active side — the fuse will still interrupt current, but the circuit remains live to the appliance after the fuse blows, creating a shock hazard during bulb or fuse replacement.

What wire size should I use for a 15 A extension cord?

For a 15 A load at standard mains voltage, use 1.5 mm² (approximately 15 AWG) three-core flexible cable, keeping the cord length under 30 m to limit voltage drop to acceptable levels. For runs over 30 m, increase to 2.5 mm² to compensate for resistance-induced voltage drop, particularly for motor loads.

Why should I never use a two-core (ungrounded) extension cord with power tools?

Power tools with metal housings rely on the protective earth conductor to carry fault current to earth if a winding failure makes the housing live. Without an earth, that fault current has no low-resistance path and the housing becomes live at mains potential. Contact with the housing and a grounded surface simultaneously causes electrocution.

What is the purpose of the earth conductor in an extension cord?

The protective earth provides a low-resistance path for fault current if insulation failure makes equipment metalwork live. This fault current trips the circuit breaker or RCD within milliseconds, removing the hazard. The earth conductor carries no current during normal operation — if it does, there is a wiring fault.

Can I join two extension cords together to reach further?

Mechanically joining connectors is acceptable in some jurisdictions for temporary use, but total cord resistance increases with length, increasing voltage drop. Total resistance also increases shock from contact with energized connectors at the join point. Use a single cord of appropriate length where possible; never use more than two cords in series for high-current loads.