Helpful video reference. We use Muck'n'Brass's UK tutorial "HOW TO WIRE A LAMP | UK 3 Pin Plug" as the video reference here. Muck'n'Brass is a London-based upcycling studio, and their walkthrough covers the full process in a UK context -- correct conductor colours, UK 3-pin plug wiring and cable grip -- making it directly applicable to anyone rewiring a lamp in the UK.
1. Decide whether this is a DIY job
The test is simple. If the lamp has a BS 1363 plug on the end and you can unplug it from the wall, it is a portable appliance and you can legally rewire it yourself. If it connects to the circuit via a ceiling rose, a fixed terminal block or a junction box above the ceiling, that is fixed wiring and should only be touched by a qualified electrician.
The same distinction applies to wall lights. A plug-in wall light with a transformer brick is a portable appliance. A wall light hardwired into a back box in the plaster is fixed wiring.
2. Inspect the old flex
Unplug the lamp and lay it on a worktop. Run the flex through your fingers from plug to lampholder. You are looking for:
- Cracking or splitting of the outer sheath, especially near the plug and at the entry point to the lamp body where the flex flexes repeatedly
- Stiffness or brittleness -- old PVC flex loses its plasticisers over the years and becomes rigid
- Discolouration from heat, particularly brown or black marks on the outer sheath near the lampholder
- Any point where the outer sheath is cut, melted or has a kink with a crease across it
Any of those is reason to replace the whole flex, not just the affected section. Do not try to repair flex with insulating tape; replace it.
3. Choose the right replacement flex
For most table and floor lamps, 2-core 0.75 mm² round flex is the correct choice. The two conductors will be brown (live) and blue (neutral). This is the standard UK colour code for flex since 2004.
If your lamp has an exposed metal body -- a steel column or a brass base that is not lacquered -- you need 3-core 0.75 mm² flex. The third conductor (green and yellow) connects to the earth terminal in the plug and to the earth connection in the lampholder, which must then be metallic. Most table lamps with a plastic or ceramic body do not need an earth.
For LED lamps (almost always under 20 W), 0.75 mm² is well over-specified but it is still the correct minimum size for flex. Do not go below it.
Braided cotton or fabric flex is available from most lamp and lighting shops and is perfectly safe. It tends to be easier to handle when threading through a decorative lamp body, and it looks better on a vintage or period lamp. PVC round flex works equally well if appearance is not a priority.
4. Thread the new flex through the lamp body
Before disconnecting the old flex, tie the new flex to the old one at the lampholder end and pull it through the lamp body from below as you remove the old flex. This saves threading blind through whatever the lamp body happens to be made of. On lamps with a narrow column, a piece of stiff wire bent into a hook works as a fishing tool if you cannot pull through.
Leave about 150 mm of flex protruding at the lampholder end and 400 mm at the plug end. You can trim to length later.
5. Connect at the lampholder
Remove the lampshade and unscrew the lampholder skirt. The two halves should separate to reveal the terminal block. Strip the outer sheath back 40 mm from the end of the flex and each conductor back 8 mm. Twist the copper strands together so none can stray outside the terminal.
Brown goes to the terminal marked L (or the one with a brass-coloured screw). Blue goes to the terminal marked N (or the one with a silver-coloured screw). Tighten the screws firmly. There should be no bare copper visible outside the terminal; if there is, the conductor is stripped back too far -- re-strip a fresh end.
Pull the flex gently from the bottom of the lamp to take up any slack, then close the lampholder halves and tighten the skirt. The flex should enter the lampholder through the gland at the base of the skirt; the gland grips the outer sheath, not the individual conductors.
6. Fit a new UK plug
Cut the flex to the length you need, then open a new BS 1363 plug. Strip the outer sheath back 40 mm and each conductor back 8 mm.
In a UK plug the terminals are arranged as follows: Live (L) is the right-hand terminal when you are looking at the open back of the plug with the earth pin at the top. Neutral (N) is the left-hand terminal. Connect brown to L and blue to N. With 2-core flex, leave the earth terminal empty.
Fit a 3 A fuse. This is the red one in most assortments. A 13 A fuse offers essentially no protection to 0.75 mm² flex: if a fault develops, the flex will melt and possibly catch fire before a 13 A fuse reacts. The 3 A fuse is specifically sized to protect the flex in small appliances.
Tighten the cable grip over the outer sheath of the flex, not the individual conductors. This is the part that holds the flex in the plug and prevents the terminal connections from being strained if someone pulls the cable rather than the plug body. Replace the cover and check it clicks shut cleanly.
7. Test before use
Fit a lamp, reattach the shade and plug in. Switch on. A healthy lamp lights immediately and stays on without flickering.
If the lamp does not light, unplug before doing anything else and re-check all connections. The most common cause is a loose terminal screw or a conductor that slipped out during assembly.
If the lamp lights but flickers, unplug and check that the conductors at the lampholder are securely terminated and that the brown wire is at L -- a reversed polarity connection (brown to N, blue to L) is both a wiring fault and means the lamp holder shell is live when the switch is off.
If plugging in trips the RCD on your consumer unit, unplug immediately. You have a short circuit, most likely from a stray copper strand touching the wrong terminal or the plug body. Reopen the plug and lampholder and re-check every connection.
When to call us
If a lamp or any other appliance is tripping an RCD and you cannot identify why, Richard can carry out a fault-finding visit across east Kent including Sandwich, Deal, Dover and the surrounding villages. Persistent RCD trips are worth investigating promptly -- they usually indicate a wiring fault somewhere in the circuit, not just in the appliance that happened to trip it last.
Electrical fault or wiring problem?
Richard provides fault-finding across east Kent, from a single lamp that won't work to a circuit that trips without obvious cause.
Contact Richard