Power Injection

I have been experimenting with various ways to build power injection cables for long runs of LEDs that will be outdoors in suboptimal conditions. Here’s what I came up with, all using parts easily procured from Amazon.

This is the power supply I chose. I like it because it is already reasonably weatherproof. I have also heard very good things about Meanwell power supplies, like the LRS-350-12, but that needs to be put in a box and you would need to wire up your own AC cable.

I found this cool tool for removing the outer jackets. If you’re following along with me, strip 5/8″ of the outer jacket.

Then strip the wires to 1/4″:

Then I crimped on these cute things. I think they are called ferules? “Insulated Bootlace Ferules,” I am told. Anyway, they make it safe to connect the stranded cable to a screw terminal.

Next, get these outdoor “junction boxes.” They come in 2 way and 3 way versions. They have cable glands on both ends which make a watertight seal as long as you use cable with a circular cross-section.

Here’s a 2 way connector, exploded:

Stick the wire through…

Technically these things have three internal connectors. I only use two for power injection. But if you are also sending WS2812 data, the third post is available.

Now you need to choose what kind of cable you are going to use for your power injection cable.

Use an online voltage drop calculator to figure out what gauge you need. This depends on whether your LEDs are 5v or 12v. If you are already building power injection cables, it sounds like you are planning long runs of power. In that case you will be much happier with 12v LEDs like ws2815.

In my case, and with a lot of testing, I decided 14awg was enough. I bought this speaker cable, but be warned: because this cable has a “slip sleeve” instead of a perfectly circular moulding, it will not make a watertight seal with the cable glands! That is OK for my application but if you want something watertight, find a circular cable.


The junction boxes are available as T’s, which is what I used at each power injection point. This is a female two-conductor “Ray Wu Connector” which powers a single LED strip that came from the factory with a male two-conductor connector.

Ferrules! Cute as a button!

Here ‘s the whole thing before screwing together?

Here are two complete assemblies.

In my situation each power supply powers 4 five-meter strips; each strip has 300 pixels at 12v.