Whether you're rewiring a table lamp, restoring a chandelier or making a new pendant light, choosing the correct cable matters.
You might see lighting flex described as 0.5mm², 0.75mm², 2-core or 3-core. These details tell you different things about the cable, and each can affect whether it's suitable for your fitting.
At Lampfix, we supply a broad range of lighting cable, including standard PVC flex, decorative braided flex and specialist cables for particular applications.
This guide explains what the sizes mean, how to estimate the electrical load and what else needs checking before you choose.
1. What Does 0.5mm² or 0.75mm² Mean?
These measurements refer to the cross-sectional area of the copper conductor inside the cable, not the overall diameter of the cable.
For example:
0.5mm² flex has copper conductors with a cross-sectional area of 0.5 square millimetres each.
0.75mm² flex has larger conductors, with a cross-sectional area of 0.75 square millimetres each.
A larger conductor can generally carry more current under comparable conditions, but the cable's actual rating also depends on its construction, insulation and operating conditions.
The outside diameter is a separate measurement.
This is particularly important for lighting, where the cable may need to pass through a narrow threaded tube, cord grip or chandelier arm.
2. Check the Voltage and Electrical Load
Start by establishing the voltage at which the fitting operates.
In the UK, the nominal mains supply voltage is 230V. Some lighting systems operate at lower voltages, such as 12V or 24V, using a suitable power supply or driver.
Next, establish the electrical load.
For a fitting with several lamps, add together their wattages, taking account of the fitting's permitted maximum load rather than simply assuming the bulbs currently installed will never be changed.
For a simple resistive load, the approximate current can be calculated using:
Current (Amps) = Power (Watts) ÷ Voltage (Volts)
Example: A three-arm chandelier
Suppose a chandelier has three traditional 60W lamps operating at 230V.
Total power:
3 × 60W = 180W
Approximate current:
180W ÷ 230V = 0.78A
This helps establish the electrical demand, but it doesn't automatically tell you which cable to use.
The cable must also be suitable for the fitting's construction, operating temperature, length and other requirements.
For modern LED fittings with electronic drivers, use the manufacturer's rated input-current information where available, as the simple watts ÷ volts calculation may not give the actual RMS current.
3. Why Low-Voltage Lighting Needs Extra Care
Lower voltage doesn't necessarily mean lower current.
Consider a 12V lighting circuit supplying twenty 3W LED lamps.
Total power:
20 × 3W = 60W
Nominal current on the 12V side:
60W ÷ 12V = 5A
That's considerably more current than the previous mains-voltage example.
Another important consideration is voltage drop.
As electricity travels through a cable, some voltage is lost because of the resistance of the conductors. The effect depends on factors including the current, cable length and conductor size.
On a 12V system, even a relatively small voltage drop can affect the performance of the lighting.
For this reason, cable sizing for low-voltage lighting must account for the complete circuit, including cable length and the equipment manufacturer's requirements.
A current calculation alone is not sufficient.
4. Do You Need 2-Core or 3-Core Flex?
The number of cores is just as important as the conductor size.
2-core flex contains two insulated conductors, normally used for live and neutral in a suitable mains-voltage application.
It may be appropriate for a light fitting designed to operate without a protective earth, such as a correctly designed Class II (double-insulated) fitting.
3-core flex contains three insulated conductors, normally live, neutral and protective earth.
It is used where the fitting requires a protective earth connection.
Many metal lighting fittings require earthing, but the correct arrangement depends on the design and electrical classification of the complete fitting.
Don't choose 2-core cable simply because an existing lampholder is plastic. Other parts of the fitting may still require earthing.
If you're restoring or modifying an older light fitting and its earthing requirements are unclear, have the arrangement assessed by a competent person before selecting the replacement cable.
5. Choosing Between 0.5mm² and 0.75mm² Flex
Both sizes are commonly found in lighting applications.
At Lampfix, we offer options including:
2 Core Round Flex, available in selected 0.5mm² and 0.75mm² variants.
3 Core 0.5mm² Flex, useful for suitable lighting repairs where a relatively slim cable is required.
3 Core 0.75mm² Twisted Braided Flex, a decorative option for suitable pendants and other lighting applications.
The correct choice isn't necessarily the thinnest cable that can carry the calculated current.
You should also check:
Current rating: Is the particular cable rated for the expected load and operating conditions?
Temperature: Will the cable be exposed to heat from the lampholder, lamp or other components?
Length: Could voltage drop become significant?
Physical fit: Will the complete cable fit the cord grip, cable entry and other fittings?
Mechanical support: Is the cable intended to support the weight of a suspended light fitting, or is separate suspension required?
Different types of cable can have different characteristics even when their conductor sizes are identical.
Decorative braiding, for example, should not be assumed to provide electrical insulation or mechanical strength beyond the cable's specified construction and rating.
6. Check the Cable Type, Not Just Its Size
Lighting cable is available in several different constructions because different applications have different requirements.
Standard PVC flex is commonly used for suitable table lamps, floor lamps, pendants and other lighting assemblies.
Decorative braided flex allows the cable to form part of the finished appearance of a fitting, with various colours, materials and constructions available.
Heat-resisting flex may be required where temperatures exceed the limits of ordinary cable insulation.
Specialist low-voltage cable is used for appropriate low-voltage applications, subject to its ratings and the requirements of the complete circuit.
Some fittings also use specialist internal wiring that is different from the external supply flex.
Check the individual product specifications before ordering. A cable intended for one application should not automatically be substituted into another simply because the conductors have the same cross-sectional area.
7. A Quick Check Before Ordering
Before choosing replacement cable for a light fitting, make sure you know:
The operating voltage and maximum electrical load.
Whether the fitting requires two or three cores, including a protective earth where necessary.
The appropriate conductor size and cable type for the application.
The required cable length, including an allowance for connections.
Whether there are any heat, voltage-drop, movement or suspension requirements.
Whether the cable will fit the existing cord grips, entries and connections.
If you're making a new pendant light, our guide to choosing the components for a ceiling pendant may also be helpful.
Electrical alterations and repairs should be undertaken by someone competent to assess and safely carry out the work. The finished fitting must be appropriately inspected and tested before use.
This guide is intended to help you understand the cable options for light fittings. It isn't a method for designing fixed building wiring or approving the electrical safety of a finished installation.
Need Help Finding the Right Lighting Cable?
Sometimes the difficult part isn't calculating the load. It's finding cable that has the correct construction, number of cores, outside diameter and appearance for an existing light fitting.
That's the sort of thing we can help with.
If you're replacing an unusual cable or matching something already fitted, send us a photograph and any markings or dimensions you have.
Tell us what type of light fitting it's for, the voltage, the relevant electrical requirements and approximately how much cable you need.
We'll help identify a suitable product from our range or a practical alternative where possible.
Browse our Lighting Cable & Flex range
Telephone: 01462 731 173
Email: sales@lampfix.co.uk