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I've been using some fairly cheap 22AWG wire for running between flexible LED strips and their transformers. Some 24V some 12V, but all well below the amperage rating for this gauge.

The wire says it's rated for 300V / 80ºC. I don't remember what it was sold as. It may even have been sold as speaker wire. It's the type with 2x separate insulated stranded cores.

So far this has all been over the surface and over fairly short distances. (2m or so) but I am now looking at doing a slightly longer run behind a wall. It would run for about 6m and partly would be between brick and skirting board, and in other parts behind plasterboard.

What do I need to consider (mainly with regards to safety and legality) when choosing wire for this job?

Are their specific standards, heat/voltage ratings or particular insulation materials that I should look out for / avoid?

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  • In NEC-influenced territory, minimum size for in-wall wiring is #18, and it must be a cable rated for in-wall wiring, not just random loose wires. – Harper - Reinstate Monica Apr 14 at 18:41
  • Thanks. No problem upping thickness to #18. What should I look for that indicates wires are rated for in-wall? standards codes etc.. UK. – Tim Apr 14 at 19:16
  • you're subject to UK codes. It's hard to advise since all the stuff North America uses low-voltage for (doorbells, thermostats) UK uses AC mains for. So I can't say how UK code treats low voltage wiring. I know EU can be pretty informal... – Harper - Reinstate Monica Apr 14 at 20:57
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Speaker wire works well for this, and you can get in-wall rated speaker wire, which usually has a 2nd common insulation around both insulated wires (like cat5). You can of course use regular mains-rated wiring in wall, but it's hard to tuck into tight spaces where you might want to hide an LED strip, and connecting to it legally takes a lot of space.

Buy stranded wire with flexible jacket materials like silicone to have an easier time "origami"-ing and hiding. You don't need oxygen free copper or anything fancy. Buy a bigger roll than you need; doubling the length is usually only 25-50% more up-front cost.

In terms of size for LED lighting, 20AWG is a good starting point for typical run lengths and a few watts. Subtract 1 gauge from 20 for every amp (12w/24w) to avoid voltage drop. So, if you need 6 amps, use 14AWG. This correlates decently to the recommended power transmission amp ratings. To be sure, that thickness is overkill in terms of fire safety but it provides voltage consistency to the strips, allowing you to very accurately match/correlate brightness levels by counting strip segments.

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Whatever wire you use, if it's going into construction, make sure it is rated for the purpose. The most common misuse I've seen is lack of FT4 rating.. I'm not going to list every type of suitable wire because it would be rather long and time consuming, especially if you're willing to run conduit.

For LVDC voltage controlled LEDs, I'm personally partial to Securex cable (Commonly used as fire alarm, doorbell or security wire). From experience, always check similar types and the cost of the next size or two up as sometimes a more common wire type of the same size or more common size of the same type is cheaper. Securex is excessive to the ratings you actually need, but it's very common so it's cheap for what you get. If the hardware store doesn't have a suitable FT4 rated, preferably stranded cable, call around to the electrical wholesalers in the area. Some types of extension cord wire can be suitable as well.

Low Voltage DC Lighting is particularly sensitive to voltage drop because of the high current per Watt, so it's best to actually calculate your voltage drop as it's rather easy. EE Stack Exchange has numerous questions regarding use of these LED strips by the way and you might want to read the canonical choosing a power supply question. Find the resistance per meter/foot for your wire size, multiply by the length to find resistance, and multiply the resistance by your anticipated current to get voltage drop. Try to keep it to only 1-2% of your 12V.

If you don't know how to calculate anticipated current, take the Watt/meter rating of your strip and multiply that by strip length to find wattage. Divide wattage by voltage to find current.

The conductors built into these strips are rather small, so for best results, you should feed positive to one end and negative to the other end of the strip. This shares the voltage drop evenly between the LEDs instead of having a high current at only one end of the strip. For long strips, instead plan to run a wire in parallel and tap it in every 3 to 4 feet.

If a phone call doesn't bother you, don't be afraid to call a few electrical wholesalers. They like selling things and they're used to doing price checks on the phone so it's not like a big box hardware store where you have to wait for the guy to walk a block to the phone. Variance in price can be huge so it can be worth calling around and pricing things out. Lastly, if you are using any significant amount of wire, check the price of a whole roll!. If you need more than the largest roll from the big box hardware store, call the wholesalers and check the price of a larger roll!. For common 14/2 NMD90, where I live it's 70 currency for 30m or 95-110 currency for 75m. A potential cost difference of 84%! It's also worth checking kijiji or whatever local buy and sell boards you have for people getting rid of leftover construction supplies, and if you can find sufficient quantity of an acceptable cable, this is usually cheapest but you have to be diligent about checking the cable type and uses. Just read the jacket of the cable and look up its ratings.

One final piece of advice, if you can't get stranded cable, it is not impossible to use solid for the bulk of the wiring, but it may result in some extra precautions like bending a spiral spring into the wire where you solder to a strip so that the solid wire can't pull with significant force on the contacts, or using insulated butt splices to switch to a short length of stranded wire before connecting to the LED strip. This may allow you to get a better wire size at the same cost.

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  • The cheap stuff I've been using says FT2 on it. So looking for FT4 is the kind of info I was after. Thanks – Tim Apr 15 at 9:54
  • The small connector wires that come with the LED strip say FT1. So presumably my surface wires are better, but still not good enough for in-wall – Tim Apr 15 at 10:01
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To prevent a fire (caused by current overheating), I like to know how much current must flow through the wire and ensure that wiring provide plenty of current capacity. You can install a fuse to ensure that the a short or similar will not cause the wire to overheat and start a fire.

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  • From my amateur calculations the current looks like about 1A, definitely well below 2A at max and I won't use anything below #20 which I think can take it easily. – Tim Apr 15 at 9:50

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