Electrical Plug Wiring Diagram

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

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

An electrical plug wiring diagram shows how the three conductors inside a mains plug connect to the correct pins: line (live) to the right-hand pin, neutral to the left-hand pin, and earth (protective earth) to the top or centre pin, following the standard for your country.

Wiring a mains electrical plug is one of the most common DIY electrical tasks, yet it is also one where errors have direct life-safety consequences. A plug wired with the live and neutral transposed, or with the earth disconnected, creates a shock or fire hazard that may not be immediately obvious — the appliance will often still function. Understanding the wiring diagram correctly, and understanding why each conductor goes where it does, is essential for anyone working on mains electrical equipment.

The most widely referenced standard worldwide is BS 1363 — the UK and many former-British-standard countries' three-pin rectangular plug. Its wiring is: - Live (Line): brown wire, connected to the right-hand pin (when viewing the plug face) - Neutral: blue wire, connected to the left-hand pin - Earth (PE — Protective Earth): green and yellow striped wire, connected to the top (largest) pin

The earth pin is larger and longer than the live and neutral pins for a critical safety reason: on socket strips with safety shutters, the earth pin mechanically opens the shutters that protect the live and neutral holes. Without the earth pin, it is not possible to insert the live or neutral pin into a shutter-protected socket.

In older UK wiring (pre-1970), the colour code was different: red for live, black for neutral, green for earth. This matters when working on older equipment.

For countries using other standards — for example, the two-pin Schuko (CEE 7/4, used across Europe), the NEMA 5-15 (North America, 120 V), or the AS/NZS 3112 (Australia/New Zealand) — the pin shapes, arrangements, and colour conventions differ, but the fundamental principle is the same: one conductor carries the supply potential (live), one provides the return path (neutral), and one connects the appliance's metalwork to earth for fault protection.

In a plug wiring diagram, always show the inside of the plug body with the terminal designations labelled. For fused plugs (BS 1363), show the cartridge fuse in series with the live terminal. The cord grip (cable anchor) should be shown clamping the outer sheath, not the individual conductors.

North American NEMA locking plugs each have a specific pin arrangement and current/voltage rating. The NEMA L14-30 (30 A, 125/250 V, 4-wire locking) and the NEMA L5-30 (30 A, 125 V, 3-wire locking) are both widely used for generators and temporary power. The L14-30 has four pins — Line 1 (black), Line 2 (red), Neutral (white), and Ground (green) — while the L5-30 has three pins: Line (black), Neutral (white), and Ground (green). Wiring the correct conductor to each pin is critical for safety. Map any NEMA plug configuration free online using the circuitdiagrammaker.com browser editor.

How to wire electrical plug wiring diagram

Identify the correct standard for your country Confirm which plug standard applies: BS 1363 (UK and many Commonwealth countries), NEMA 5-15 (North America), Schuko CEE 7/4 (Europe), or AS/NZS 3112 (Australia/New Zealand). The pin layout, fusing requirements, and wire colours differ. Do not assume a universal colour code applies.
Open the plug body and identify the terminals Remove the plug body retaining screw. Open the plug to reveal the three terminals (or two for a double-insulated appliance). Identify the earth terminal (E or green/yellow), neutral (N or blue), and live (L or brown). For BS 1363 plugs, locate the fuse carrier in the live circuit.
Prepare the cable Pass the cable through the cord grip. Strip the outer sheath by approximately 40 mm (for BS 1363 plugs) to expose the three conductors. Strip each conductor's insulation by approximately 5 mm. Twist the wire strands tightly. Do not nick the strands with the stripper — damaged strands reduce the conductor's current-carrying capacity.
Connect the earth wire first Connect the green-and-yellow wire to the earth (top) terminal. Ensure no bare copper is visible outside the terminal. The earth wire is intentionally cut slightly longer than the others inside the plug, so if the cord is yanked hard enough to pull through the cord grip, the earth is the last conductor to disconnect.
Connect neutral and live Connect the blue wire to the neutral terminal (left in BS 1363). Connect the brown wire to the live terminal (right in BS 1363). For screw-barrel terminals, insert the wire and tighten the screw until resistance is felt — do not overtighten and snap the screw. Tug each wire to confirm it is secure.
Check the fuse (BS 1363 only) Fit a cartridge fuse of the correct rating for the appliance's wattage: 3 A for under 700 W, 13 A for 700 W to 3 kW. Confirm the fuse clips securely into the fuse carrier. The fuse is in series with the live terminal.
Close the plug and tighten the cord grip Tighten the cord grip to clamp the outer sheath firmly. No individual conductor insulation should be visible outside the plug body. Close the plug body and tighten the retaining screw. Test with a plug tester or multimeter to confirm correct wiring before connecting to a live socket.

Specifications

UK standard	BS 1363, 13 A / 250 V AC, 3-pin rectangular
Live wire colour (IEC 60446 / BS 7671)	Brown
Neutral wire colour	Blue
Earth wire colour	Green and yellow stripes
Fuse type (BS 1363)	BS 1362 cartridge fuse: 3 A or 13 A
North America standard	NEMA 5-15, 15 A / 125 V, 2-pin + earth; live=black, neutral=white, earth=green
Australia/NZ standard	AS/NZS 3112, 10 A or 15 A / 230 V; live=brown, neutral=blue, earth=green-yellow (post-2006)
Flex conductor cross-sections (typical)	0.75 mm² (light duty lamps) to 2.5 mm² (high-power appliances)

Safety warnings

Mains plug wiring involves lethal voltages (230 V AC in the UK and most of the world; 120 V AC in North America). Always disconnect the plug from the socket before opening or working on it. Never work on a plug that is connected to a live socket.
In many jurisdictions, wiring or rewiring fixed electrical installations must be done by a licensed electrician. Replacing the plug on a flexible appliance cord is generally permitted for competent persons, but always verify the law in your country or region.
All work must comply with applicable wiring standards: BS 7671 (UK), NEC/NFPA 70 (USA), AS/NZS 3000 (Australia/New Zealand), or IEC 60364 (international). These standards exist because improperly wired plugs cause electrocution fatalities and house fires every year.
Never use a plug with a cracked or damaged body. Hairline cracks in the body allow moisture ingress and expose internal terminals. Replace a damaged plug body — do not repair it with tape.
The earth (green/yellow) conductor must never be omitted on Class I appliances. A disconnected earth means that if a live conductor contacts the appliance's metalwork, the metal parts become live at mains voltage — a fatal shock hazard.

Tools needed

Flat-blade screwdriver (plug retaining screw and terminal screws)
Wire stripper (sized to conductor cross-section)
Plug tester / socket tester (to verify correct wiring after reassembly)
Multimeter (for continuity and earth bond testing if needed)
Side-cutter pliers (for trimming conductors to length)
Tape measure or ruler (for measuring strip lengths)

Common mistakes

Swapping the brown (live) and blue (neutral) wires, which leaves the appliance's internal switch in the neutral rather than the live circuit — creating a shock hazard in switched-off appliances.
Cutting all three conductors to the same length, so the earth wire is not the longest — if the cord is yanked through the cord grip, the earth should be the last to pull free.
Leaving bare strands of copper sticking out from the terminal, which can contact the adjacent terminal and cause a short circuit.
Failing to tighten the cord grip onto the outer sheath, allowing the individual conductors to take the mechanical strain when the cord is pulled.
Fitting the wrong fuse rating — particularly fitting a 13 A fuse in a plug powering a low-current appliance like a lamp or clock, providing essentially no overcurrent protection for the flex.
Re-using an old plug body that has scorched or blackened terminals — once a terminal has overheated, its contact resistance is permanently elevated and it should be replaced.

Troubleshooting

Appliance trips the RCD (residual current device) immediately on connection: Cause: An earth fault in the appliance, or the live wire inside the plug is contacting the earth terminal or pin Fix: Disconnect the appliance. Open the plug and inspect the wiring for strands touching the wrong terminal or for damaged insulation. Carry out an insulation resistance test on the appliance if available. If the appliance itself has an internal fault, it requires professional repair.
Plug body gets warm or hot during normal use: Cause: Loose terminal connection causing arcing and high contact resistance; overloaded circuit; or fuse carrier is making poor contact with the fuse Fix: Disconnect immediately. Open the plug and tighten all terminal screws. Check that fuse clips are firm. Verify that the appliance load does not exceed the plug and cord rating. Replace any discoloured or scorched components.
Plug tester shows incorrect wiring after reassembly: Cause: Live and neutral are transposed, or the earth is not connected Fix: Open the plug immediately. Identify brown (live) to right terminal (L), blue (neutral) to left terminal (N), green/yellow to top terminal (E). Reconnect and retest. Do not use the appliance until the tester shows correct wiring.

Frequently asked questions

What are the wire colours in a UK BS 1363 mains plug?

In a UK mains plug (BS 1363), brown is live (connected to the right-hand pin), blue is neutral (left-hand pin), and green-and-yellow striped is earth (top pin). These colours follow IEC 60446 and replaced the older red/black/green scheme after 2006 harmonisation.

What happens if live and neutral are swapped in a plug?

The appliance will usually still work, because AC power flows through both conductors. However, the appliance's internal switching (if any) will interrupt the neutral rather than the live, leaving live voltage present at internal contacts even when switched off. This is a serious shock hazard, particularly on lamp holders and switches.

Does a 2-pin plug need an earth wire?

No — but only if the appliance is double-insulated (Class II), indicated by the double-square symbol on the appliance. Double-insulated appliances have two layers of insulation around all live parts, making an earth connection unnecessary. Class I appliances (with exposed metal parts) require a 3-pin earthed plug.

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

The fuse should be as close to the appliance's rated current as possible without being lower. Use a 3 A fuse (red) for appliances under 700 W (lamps, radios, small chargers). Use a 13 A fuse (brown) for appliances from 700 W to 3 000 W (kettles, toasters, computers). Using a 13 A fuse on a low-power appliance provides minimal short-circuit protection.

What is the purpose of the cord grip inside a mains plug?

The cord grip (cable clamp or strain relief) anchors the outer sheath of the flex cable so that if the cable is pulled, the mechanical force is transferred to the outer sheath rather than to the individual conductor terminals. Without it, pulling the cable could pull a conductor off its terminal, creating a loose live wire inside the plug body.

How do I wire an L14-30 electrical plug?

The NEMA L14-30 is a 30 A, 125/250 V 4-wire locking plug used on generators and transfer switches. Connect the black wire to the X terminal (Line 1, hot), the red wire to the Y terminal (Line 2, hot), the white wire to the W terminal (neutral), and the green or bare wire to the G terminal (ground). Always confirm the terminal labelling on your specific plug body before connecting, as some manufacturers mark them differently. The L14-30 plug requires a matching L14-30R receptacle and a 4-conductor cable rated at least 30 A (typically 10 AWG for short runs).

How do I wire an L5 electrical plug?

The NEMA L5-series includes the L5-15 (15 A, 125 V) and L5-30 (30 A, 125 V) 3-wire locking plugs. Each has three terminals: X (Line, black wire), W (Neutral, white wire), and G (Ground, green or bare wire). There is no second hot leg, so these plugs supply single-phase 120 V only. Use cable rated for the plug's amperage — 14 AWG for L5-15, 10 AWG for L5-30 on typical short runs. Tighten terminal screws to the torque value stamped on the plug body to ensure a reliable connection.

Related diagrams

Free electrical calculators

Edit this diagram free in the online editor