3-Prong Plug Wiring Diagram: L, N, and Earth Connections Explained

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A reference wiring diagram for 3-pin earthed plugs, covering terminal identification, conductor colour codes, and correct connection for both UK BS 1363 and US NEMA 5-15 plug types.

A three-prong (three-pin) earthed plug connects an appliance to the mains supply via three conductors: Live (Line), Neutral, and Earth (Ground). The purpose of the earth conductor is safety — it provides a low-impedance fault current path that causes the protective device (fuse or circuit breaker) to operate if the appliance casing becomes live, instead of allowing that energy to flow through a person.

**UK BS 1363 plug (13 A, 230 V):** The three rectangular pins are of different sizes: the earth pin is the longest and largest (8 mm × 4 mm), the live and neutral pins are 6.35 mm × 4 mm. The earth pin opens the protective shutters on the socket before the live and neutral pins insert — a critical passive safety feature. - **Brown** = Live (L), top right pin when plug face is viewed - **Blue** = Neutral (N), top left pin - **Green and yellow** = Earth (E), the large top-centre pin

BS 1363 plugs contain an internal cartridge fuse (3 A, 5 A, or 13 A) in the Live conductor, providing appliance-level overcurrent protection.

**US NEMA 5-15 plug (15 A, 120 V):** The plug has two flat parallel blades and a round earth pin below. The neutral blade is slightly wider than the live blade, preventing reversed polarity insertion. - **Black** = Hot (Line/Live), narrower flat blade - **White** = Neutral, wider flat blade - **Green or bare copper** = Ground (Earth), round pin

For hardwired installations and flexible cord sets, conductor identification follows IEC 60446 (international standard): brown = L, blue = N, green/yellow = earth. Older UK wiring used red (L), black (N), and green (earth) — these colours may still be found in older installations.

**Connection torque:** All screws on plug terminals must be tightened firmly. A loose live terminal is the most common cause of plug overheating and fire.

How to wire 3 prong plug wiring diagram

Gather materials and switch off at the source Ensure the plug is fully disconnected from the mains socket before wiring. Have the correct plug for your region and a flexible cord of the appropriate current rating. Do not work on any plug or cable while it is connected to a live outlet.
Open the plug and identify terminals Remove the plug cover screw and open the plug body. Identify the three terminals: Live (L or marked with a small fuse holder in BS 1363), Neutral (N), and Earth (E). In a BS 1363 plug, the earth terminal is at the top (longest pin), Live is bottom right, Neutral is bottom left when viewed from the terminal side.
Prepare the cable Strip the outer sheath of the cable by approximately 40–50 mm, being careful not to nick the inner conductor insulation. Then strip approximately 8–10 mm of insulation from each inner conductor. Twist the stranded conductors and tin them lightly with solder if required by your region's installation standards.
Connect the Earth conductor first Connect the green and yellow (or bare copper for US) earth conductor to the earth terminal. Ensure there is sufficient conductor length so that if the cable is pulled, the earth conductor is the last to pull free — it must be the longest conductor inside the plug. Tighten the terminal screw firmly.
Connect Neutral Connect the blue (or white for US) neutral conductor to the neutral terminal (N). In a BS 1363 plug, this is the left terminal. In a NEMA 5-15 plug, this is the wider flat blade terminal. Tighten firmly and ensure no bare conductor is exposed outside the terminal.
Connect Live Connect the brown (or black for US) live/hot conductor to the Live terminal (L). In a BS 1363 plug, this passes through or next to the fuse carrier. Confirm the correct fuse rating is installed in a BS 1363 plug. Tighten the terminal screw firmly.
Secure cord grip and close the plug Tighten the cord grip over the outer cable sheath — not over the inner conductors. Verify no bare conductor is exposed. Reassemble the plug cover and tighten the retaining screw. Inspect the plug before use: all wires should be invisible from outside, and the plug face should be undamaged.

Specifications

UK BS 1363 plug rating	13 A, 230–240 V AC, 50 Hz
US NEMA 5-15P plug rating	15 A, 120 V AC, 60 Hz
Earth conductor colour (IEC/UK)	Green and yellow
Live/hot conductor colour (IEC/UK)	Brown
Neutral conductor colour (IEC/UK)	Blue
Live/hot conductor colour (US)	Black
Neutral conductor colour (US)	White
BS 1363 cartridge fuse options	1 A, 3 A, 5 A, 10 A, 13 A (BS 1362)

Safety warnings

All fixed wiring must be carried out by a qualified electrician in accordance with the applicable standard for your jurisdiction: BS 7671 (UK), NEC/NFPA 70 (US), AS/NZS 3000 (Australia/New Zealand), or IEC 60364 (international). Mains voltage is lethal.
Always disconnect the plug from the socket before opening it or working on the conductors. Never assume a socket is dead without verifying with a non-contact voltage tester.
In the UK, fitting a plug without an appropriately rated fuse in a BS 1363 plug leaves the flexible cord unprotected. Always select the correct fuse rating for the connected appliance.
Never use a plug with a cracked body, exposed conductors, or a loose pin. Damaged plugs must be replaced immediately. Do not use tape to repair a damaged plug.
This diagram is provided for reference and educational purposes. Mains wiring work may be restricted to licensed electricians in your jurisdiction. Always comply with local regulations.

Tools needed

Flat-blade and cross-head (Pozidrive or Phillips) screwdrivers
Wire strippers (suitable for 0.75–2.5 mm² flexible cord)
Multimeter or non-contact voltage tester
Insulation resistance tester (for verification in professional installations)
Soldering iron (optional, for tinning stranded conductors where permitted)

Common mistakes

Reversing Live and Neutral — the appliance operates but the switch disconnects the neutral, leaving the appliance live at the switch.
Omitting or not securing the cord grip, so a pull on the cable stresses the individual terminal connections rather than the outer sheath.
Incorrect fuse rating in a BS 1363 plug — fitting a 13 A fuse on a low-power appliance provides no protection to the appliance's own flexible cord.
Leaving excessive exposed bare conductor at each terminal, creating a risk of accidental contact between adjacent conductors or with the plug casing.
Not tightening terminal screws fully. A loose Live terminal is the leading cause of plug overheating and fire.

Troubleshooting

Plug feels warm or hot to the touch after use: Cause: Loose terminal connection, undersized cable, or appliance drawing more current than the cable/plug rating allows Fix: Immediately disconnect the plug and allow it to cool. Open the plug and check all terminal screw torque. Check that the cable rating matches the appliance current draw. If the plug or cable shows signs of heat damage, discard and replace.
Appliance does not work from plug; no power: Cause: Blown fuse (BS 1363 plug), open circuit at a terminal, or loose conductor Fix: For BS 1363 plugs, replace the fuse with a correctly rated fuse. If the new fuse immediately blows, the appliance has a fault — do not use. Open the plug and verify continuity through each terminal. Check for loose or disconnected conductors.
RCD (GFCI) trips whenever this appliance is plugged in: Cause: Earth leakage fault in the appliance — current is flowing to earth via an unintended path Fix: Do not bypass or reset the RCD and continue using the appliance. An RCD/GFCI trips to protect against shock. Have the appliance inspected by a qualified technician. Do not use the appliance until cleared.

Frequently asked questions

What happens if I connect live and neutral in reverse in a plug?

The appliance will usually still function, but the switch in the appliance will disconnect the neutral rather than the live conductor. This means parts of the appliance remain live even when switched off, creating a shock hazard during maintenance. Always connect L and N correctly per the conductor colour code.

Do I need to connect the earth wire in a plug?

Yes, if the appliance has a metal enclosure or is designated as Class I (earthed). Omitting the earth conductor means the casing cannot be safely discharged in a fault — a person touching the casing could receive a lethal shock. Class II appliances (double-insulated, marked with a double-square symbol) do not require an earth connection.

What fuse rating should I use in a UK BS 1363 plug?

Choose the fuse rating closest to but above the appliance's rated current. Calculate current by dividing rated watts by 230 V. Appliances up to approximately 700 W use a 3 A fuse. Appliances from 700 W to 3000 W use a 13 A fuse. Using a 13 A fuse in a low-power appliance provides inadequate protection for the appliance's own flex.

What does the cord grip (strain relief) in a plug do?

The cord grip clamps the outer sheath of the flexible cord, not the individual conductors. This ensures any pull on the cable is absorbed by the cord grip rather than tugging the individual wire terminals loose. Always secure the cord grip — a loose connection at the terminal caused by an unclamped cord is a common fire and shock hazard.

Are UK and US plug conductors the same colour?

No. UK and IEC-standard flexible cord uses brown (live), blue (neutral), and green/yellow (earth). US wiring uses black (hot/live), white (neutral), and green or bare copper (ground). These colour codes do not overlap — always check which standard applies to the cable you are working with.

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