What Size Cable Do You Need for Lighting? A Complete Guide

What Size Cable Do You Need for Lighting? A Complete Guide

Have you ever paused to think about what size cable for lighting is used in your home? Light cables are used everywhere as long as lighting is needed. These cables have to be specialised to ensure the installation is reliable and durable. 

But considering there are so many applications of lighting cables, you’ll also find a wide array of lighting cables according to size, design, and type. This can make it challenging to choose the right cable for your specific requirements. 

Bearing that in mind, we’ve done a bit of research and put together this complete guide to help homeowners like you looking for lighting cables. 

What’s a Lighting Cable?

Just like most other electrical installations, in lighting, wires are needed to supply electricity safely to the lighting equipment. The equipment can be a vast array of light-producing pieces, such as LED strips, bulbs, neon signs, softboxes, lamps, and more. 

Depending on the type of equipment you’re supplying power to, you’ll need to choose the type and size of the cable. This ensures the cable can handle the current flowing through it to make the lighting equipment produce just the right brightness while reducing risks of overheating. 

For most basic home lighting needs, like a pendant over the table or a bedside lamp, the lighting equipment often comes with the right cable size and type. There, you’re sorted. 

But then you start thinking about under-cabinet LEDs, garden lights, or a new ceiling rose… that’s when the question “what size cable for lighting” starts to itch. And for commercial jobs? Whole different ball game. Large-scale or specialised applications need more complex configurations, real expertise, and sometimes even custom cables. Blimey.

Why Cable Size Isn't Just a Number

Picking the right cable for lighting isn’t the same as grabbing any old USB lead. You don’t just choose one that fits. The size, that is, the cross-sectional area, measured in square millimetres (mm2), is very critical. Think of it like a motorway. A single-track lane (thin cable) will cause a traffic jam (electrical resistance) if too many cars (amperes of current) try to get through. The result is overheating, fraying, and potential failure. 

What Size Cable For Lighting Is Right? Look At Current, Distance, and Safety

It’s easy to assume that since lighting isn’t as intensive as powering equipment like a toaster, it doesn’t need much power. And so, any cable can do. Well, that’s not entirely true. To determine the right cable size for lighting, you must look at three key things:

1. The Current Demand (Amps)

How much current do your lights actually need? A 40-watt bulb requires far less than a string of 50-watt halogen spots. You need to add it all up.

2. Distance Covered 

This is a biggie, especially for what size cable for outdoor lighting. If the cable has to cover a longer distance, the higher the resistance will be. With a rise in resistance, there will be a “voltage drop.” This means your lovely bright lights at the start of the run are dazzling, but the ones at the end are gloomy. To compensate for long runs, you often need a larger cable size.

3. Safety

Safety goes hand in hand with the installation method. Is it buried in a wall? Is it clipped to a beam? Or buried directly in the ground? The method of installation affects how well the cable can dissipate heat. A cable in a bundle or under insulation can’t cool as easily. This means the size has to be bigger to reduce resistance and, consequently, the heat produced.

Overlooking these three key considerations isn’t just a technical fudge; it also goes against the BS 7671 Wiring Regulations, the UK’s bible for electrical safety. So, non-compliance isn’t worth the risk at all.   

A Practical Look at Common Lighting Cable Sizes in the UK

Alright, now let's get down to brass tacks. What do you actually find in UK homes? Here’s a rough guide, but always work closely with a qualified electrician or ensure you do your calculations for each specific wiring job. 

Standard Indoor Lighting Circuits

So, you want to light up your indoors? For a typical ceiling light, wall light, and indoor switch, here are the right cable sizes to use:

  • 1.0 mm² Twin and Earth (T&E): This is the classic, and you’ll find it commonly used for final circuits to light fittings and for switch drops. It can safely deliver up to 16 amps when clipped directly to a surface. That’s more than enough for a circuit of most standard light bulbs. When wiring most indoor room lighting, this is the right cable for you. 
  • 1.5 mm² Twin and Earth (T&E): This cable is slightly thicker and sturdier. You’ll mostly find it in older installations, but it’s also used for lighting circuits that power several socket outlets. It’s also the ideal choice when you have to run the cable over a long distance to reduce voltage drop. 

When You Need to Go Bigger: Kitchens, Garages & Extensions

If you’re planning something more substantial than an ordinary light bulb, you need to upgrade your cables. Such cases are when wiring workshop lighting, kitchen downlighters, or a garden room. 

In such cases, you must do total load calculations. If installing ten 10-Watt LED downlights, that’s only 100 watts of load (less than 0.5 amps). A 1.0mm2 cable handles this perfectly. But when it’s ten 50-watt halogen downlights, that’s 500 watts (over 2 amps). 

You also need to factor in the running distance from the consumer unit. In that case, a 1.5mm2 cable might be the safer and more efficient option to prevent dimming. 

The Great Outdoors: What Size Cable for Outdoor Lighting?

What size cable for lighting the outdoors do you need? The conditions outdoors are harsh: dampness, temperature swings, UV exposure, and risk of physical damage. So, the cable size is only part of the puzzle here. 

  • The Cable MUST Be Suitable:  For outdoor lighting, you can’t use the standard indoor T&E cable. Instead, you need to choose cables that have UV-resistant and weatherproof sheath. Good examples are the Armoured Cable (SWA) or the HO7RN. SWA comes with a steel wire armour for mechanical protection, which is important if burying it. 
  • Size for the Distance: If running the cable to a garden shed, driveway lamp post, or patio lights, it can be long. Here, voltage drop is the enemy you must take care of. A 1.5mm2 cable might be enough for a short run to power a few LED spike lights. But a run to a summerhouse some 30 metres away, powering several lights, will require something bigger, like a 2.5mm2 or even bigger. You just have to do the math to figure it out. 
  • Protection is crucial: All electrical cables running outdoors must be protected using a suitable RCD (Residual Current Device). If burying the cable, make sure it’s at the correct depth (often over 450mm) and laid with a warning tape above it. Check out the Electrical Safety First website for a clear guideline on this. 

 

Navigating the Maze: Specialised Lighting Setups

When considering what size cable for lighting, you need to understand that not all lighting is a simple bulb in a socket. Some popular modern setups need extra thought. 

Dimmable Circuits & Smart Lighting

Planning to install a smart or dimmer switch? While the cable size usually doesn’t change, the type of wiring might. Some advanced dimmers, like trailing-edge dimmers for LEDs, are sensitive to poor connections. 

To provide a clean power supply and prevent flickering, ensure you have solid, proper-sized cables like a good 1.0mm2 or 1.5mm2..

LED Neon Signs

These are also another beast when it comes to wiring. You must figure out the size of the cable an LED neon sign needs to avoid a flickering mess or a dim sign.  Also, if the cable isn’t right, the colour consistency will become an issue. If the cable is too thin or runs a long distance, there’ll be a higher resistance. This means the driver will have to work extra hard, which might give birth to inefficiencies, heat build-up, and potential early failure. 

So, here are a few rules of thumb when determining what size cable for lighting an LED neon sign. If it’s a regular 12V or 24V LED neon sign, and the cable run from the driver to the sign is below 3 metres, the cable supplied with the sign is often suitable. That’s a decent 1.5mm2 flex cable. 

If you’re covering a longer distance, say mounting the sign high on a wall, and want to hide the driver in a cupboard some 5 meters away, you need to do some math. You can upgrade to  2.5mm2 twin-core low-voltage cable. This will help preserve the brightness and support an even glow from end to end. 

LED Strip Lighting Galore

LED strips running under cabinets and shelves offer a great ambience to a space. They’re low voltage (12V or 24V DC), which means you have a driver (transformer) plugged into the mains, then you run the low-voltage cable to the strips. 

Here, your biggest challenge is voltage drop. Even a small drop over several metres can make the last section of the strip appear dimmer than the beginning. The fix to this? Use a thicker low-voltage cable instead. For 12V strips, 1.5mm2 or 2.5mm2 twin flex cable is recommended, especially for runs of several metres. 

 

How to Choose Your Cable Size for Lighting

If you feel overwhelmed in choosing the right cable size, no need to. Simply break down the task. 

  • List the Lighting Gear: These include the light fitting, its wattage, and where to install it. 
  • Map the cable run: Try your best to map the cable accurately to find how long it has to travel from the consumer unit or your last connection point. 
  • Do the Calculations: Now, sum up the wattage of your loads, then convert them to amperes (Amps = Watts/Volts). You can use a reputable online cable size calculator. Key in your total amps, cable length, and installation type to get a cable size suggestion. 
  • Consider the Environment: Whether it's indoor or outdoor installation, consider the depth, then choose the cable type (SWA, T&E, etc).  

Always follow the golden rule of choosing a cable size, which is to consult a pro if you’re not sure. Ask for a quotation from a qualified electrician if you’re dealing with complex cable installations. 

Final Thoughts

Choosing what size cable for lighting is a fundamental part of doing a light installation, not an afterthought. It's what makes the difference between a system that is safe, reliable, and brilliant for years, and one that is a potential hazard or headache.

Even though understanding the principles is fantastic, don’t let confidence override caution. Use this guide to help you ask the right questions, understand the quote from your electrician, and make informed decisions. 

 

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