Wire thickness needed

When hooking up LED strip it can be hard to figure out what kind of wires you need to use. For each of my dimmer boards I’ve listed how to connect all the wires, but what thickness should these wires be?

First off, let’s set the general rule we are using copper cables and not something else like CCA speaker wire.

Designing for worst case scenario

All calculations made are designed for the worst case scenario which is full brightness. Now I realize you won’t be running your LED strips set to full brightness most of the time (or ever really with very high power versions), that’s why you’re building a dimmer! Still, I tend to design all my setups in such a way that if I do need full brightness or something goes wrong, the whole setup (power supply + cabling + dimmer + cooling) can handle the amount of power that CAN be output to the LED strip, that way a fire is a lot less likely to occur!

With that said, keep reading until you reach the “Are you insane?” section!

Thickness calculation method

To calculate the thickness needed first we need to know how long the cable needs to be. As a general rule of thumb a loss of about 5% (voltage drop) is acceptable for most DC connections. The amount of loss a cable will give is directly dependant and the length of the cable. An AWG22 cable might be fine for 20cm but if you need a much longer distance like say 5m for example, you are going to need a much thicker cables.

The second important factor is how many amps need to travel over the cable. Voltage doesn’t play a direct factor in determining cable thickness but does determine the amount of wattage that can travel over the cable in the end and the amount of loss that will occur.

So Amperage + Length determines cable thickness. Take a look at the following table. This table is in mm2 not wire gauge!:

Table borrowed from 24volt.co.uk

This table makes it very easy to see the thickness of cable you should aim for when using 24v volt. Since this chart is in Amperage and not wattage, the same values should apply to 5v and 12v too, only the percentage drop will change but you should still be in the safe margin.

As an example, let’s say you have a 5m (~16.6 feet) LED strip which uses 100 watts of power at maximum brightness. The cable you want to use needs to be 5 meters, using 12v this is 8,33Amps but using 24v this is only 4,16Amps! To transfer ~8A safely you need a 1.5mm2 cable switching that up to a 24v LED strip and power supply you now only need to transfer the 4,16Amps and thus a 0.75mm2 cable (basically half the thickness) will do just fine. To translate mm2 to gauge see the following table:

Going by what this table says for 12v 8Amps you need a 14 gauge cable. If you where to buy everything 24v you’d only need to transport ~4Amps of power and thus only need a 22 to 20 gauge cable. Basically, this is for the same reasons as explained in my “12v vs 24v” article, using a higher DC voltage allows you to use less copper and thus save in cost! You’ll also run into less problems with the LED strip fading at the far end.

For hooking up analog white LED strip the + and – wire need to be the same thickness.

Examples

  • 5m, 12v, warm white LED strip using 16/m
    • 5m * 16w =80w | 80w / 12v ~ 7 Amps
      • Leads from dimmer to LED strip are 2m
        • To transport 7 Amps over 2m you need a minimal wire thickness of 1.5mm2 or between 16 and 14 gauge
  • 5m, 24v, warm white LED strip using 14.4W/m
    • 5m * 14.4w = 72w | 72w / 24v = 3 Amps
      • Leads from dimmer to LED strip are 2m
        • To transport 3 Amps over 2m you need a minimal wire thickness of 0.75mm2 or between 22 and 20 gauge
      • Same scenario but now distance to LED strip is 10m from dimmer to LED strip
        • To transport 3 Amps over 10m you need a minimal wire thickness of 1.5mm2 or between 16 and 14 gauge
  • 5m, 5v, 60LEDs/m, WS2812b RGB strip using 60mA per LED
    • 60LEDs/m * 5v = 300 | 300LEDs * 0.06A = 18 Amps
      • Leads from the dimmer to LED strip are 5m
        • To transport 18 Amps over 5m you need a minimal wire thickness of 2.5mm2 or 10 gauge

Are you insane?

According to the above calculations you need some thick cables to connect you LED strips to your boards! Most LED strips come with some short leads which have a fraction of the thickness, so how do the above calculations make sense?

Cable thickness scales directly with distance. For a 10cm lead you aren’t going to need 2.5mm2 or 10 gauge wire. Something like 0.5mm2 or 24 gauge (or even less) will work just fine. Personally I use a spool of 0.75mm2 or 20 gauge wire for my short leads which don’t exceed 1 meter. So if the dimmer is close to the LED strip, you don’t have too much to worry about. It’s when the dimmer or power supply is a few meters or 10’s of feet away that you need to pay close attention to cable thickness!

To purchase cable, see the Tools and Equipment article I have listed several different types there which can be used for power or signal wires (signal wires can be a lot thinner!).

Additional information

Sometimes there are special cases you need to take into account when calculating wire thickness.

Double feeding a LED strip

If you are, for instance, single feeding a 100w LED strip which runs at 24v and needs 5 meters of cable this requires 4,16A of power and thus a wire thickness of 0.75mm2 to transfer it over those 5 meters. If you however double feed the cable (from both ends) the requirement per cable is only ~2A so thinner cables can be used!

*Power distribution is never 100% equal and it’s good practice making sure both ends can handle the full load, maybe use 2/3rd of the thickness instead of half for instance

Analog RGB(W)

When using RGB(W) strip you have 4 negative wires but only a single positive wire. To be able to handle the same amount of current all the negative wires can handle, the positive wire should in theory be 4 times thicker than the negative wires. In reality that would make for a very thick (and thus expensive) cable so generally twice the size cable is recommended. If each LED strip color can handle say 1Amps using 24v, make sure the positive + cable can handle at least 2Amps but preferably more.

Digital RGB

Digital RGB has its own set of rules. If we’re talking about APA102 there is a positive, negative, and separate data and clock wires. For WS2812b there is a positive, negative and only a single data wire. The thickness of the data wire mostly isn’t that important, even a dupont wire could do just fine. The thickness of the positive and negative wires are important though! Because most of these strips only uses 5v it means you are dealing with much more amperage than with 12v or 24v LEDs.  Any decent length Digital RGB strip can easily pull more than 10 Amps so cable thickness is important! Check the above table to calculate what you would require. An example, 10Amps will need 4mm2 or 6 gauge for 10 meters of cable length, so it’s strongly advised to try and keep wire length after the power supply as short as possible!

Alternate ways

For instance in this QuinLED-Quad article I have diagrams of how it can be hooked up optimally. There are however different ways that sometimes surface on the internet, I mostly don’t recommend these but they are:

2 sided single feed

If you want to make sure all LEDs within a strip are evenly lit you can connect positive on one end and the negative current on the other side of the LED strip. This way power always needs to travel the same amount of distance through the strip and in theory voltage drop will thus also always be the same for each LED. Although this is a viable way of doing it, especially in larger LED installations this can be confusing to hook up. This also doesn’t solve the problem of voltage drop within the LED strip but basically works around it by using the effect instead of solving it. The result, although evenly lit will still result in dimmer LEDs and also still cause a lot of extra heat because of all the current traveling through the LED strip.

Only double feeding positive +

When using RGBW strip, each color (Red, Green, Blue and White) have their own negative line going to the strip. The positive line/rail is shared among them. In my opinion you need to make sure that the positive rail is thicker and uses thicker cables so to be able to match the 4 negative rails on full brightness (RGB displaying white + white). In reality the cables connected to the LED strips are all the same thickness so the positive cable needs to conduct a lot more current then the other cables. A way to fix this is to only run a positive cable to the other side of the strip and only double feed the positive rail. Since the current running through the negative wires is a lot less, it’s voltage should drop off less and sometimes you can get away with only double feeding the positive rails that way.

Personally I’d advise, if you are planning this, to plan for double feeding all the rails (positive and negative) or to middle feed to prevent an imbalance in the strip. This will also make sure you get the actual intended maximum brightness out of the strip and don’t cause a very high heat build-up at the side where all the negative wires are connected. With that said, for some projects only double feeding the positive current might be enough and workable.

Here is an example how to hook this up using the QuinLED-Quad: