Due to the low-current nature of most LED light systems, most of the wire you find lying around should do the job. There are, however, a few considerations you should make to ensure what you’ve got will fit the bill.
Solid Core vs. Stranded Wire
Wire comes in a couple flavors: solid core and stranded. Solid core wire consists of a single solid conductor (usually copper), wrapped by a plastic insulating jacket. Stranded wire contains a number of individual conductors in a bundle which is then wrapped in an insulating jacket.
In the past, I’ve recommended stranded cable for this application, but have changed my mind over the past few months. While stranded is much more flexible, it’s also more difficult to work with and sometimes requires a little bit of solder to stiffen it up enough to jam in a connector. For this reason, I’ve since changed my recommendation to solid core wire for LED applications. It’s definitely flexible enough to do the job and it’s much easier to make connections with.
Selecting Proper Gauge
It’s important to select the right gauge of wire for your system. Bigger wire is nearly always better (the main problem with big wire is its flexibility and difficulty of termination) but most LED grow lights don’t draw a whole lot of current and will not require large wires. When it comes to choosing wire, you’ll see that the wire has an AWG (American Wire Gauge) designation. AWG ratings for wire work in a funny way – the larger the number, the smaller the wire. For example, the diameter of a 16-gauge wire is physically larger than that of an 18-gauge wire.
There are 2 things to consider when selecting the size of wire for your system: voltage drop and ampacity of the wire.
Although it’s an excellent conductor, copper does have inherent resistance. The longer your run of cable, the more resistance (measured in ohms) you’re going to see on your circuit – just due to the cable itself. Also, as your wire gets smaller, resistance increases, since there is a smaller area for electrons to flow through. So why does this matter? Well, due to Ohm’s law, as resistance increases, voltage will decrease. If your wire is too small and the run too long, you may find that the 36V your driver is putting out is actually only 35V by the time it’s traveled the length of the wire. This voltage drop could cause problems in a constant voltage system where small changes in voltage can produce large changes in current.
Try punching in a few numbers on an online voltage drop calculator to see what type of voltage drop you can expect with varying currents, wire sizes, and run lengths.
Most importantly, you’ll need to make sure the wire you choose is large enough to handle the current you’re sending through it. If your wire is too small, it can heat up due to resistance, and this can be dangerous. If the wire heats up too much, you can melt the jacket on the wire, and, in the worst case scenario, start a fire. Another spec to take into consideration is the voltage rating of your wire. Often, smaller wire is rated for 300V, so don’t exceed this on your circuit. Usually, the connectors in the circuit are rated for less than this – most are 250V – so it’s a good idea to keep the voltage low anyway.
Realistically, since the majority of DIY LED setups have relatively short wire runs and are connected in series with a low amount of current flowing through each chip or board (often 700mA – 3A at most), you can get away with some very small wire. However, if you happen to be driving a large number of lights hard in parallel, you could end up with enough current to make you think twice about the wire you use. Have a look at the chart below for the current handling ability of different wire gauges (the numbers are pulled from the Wikipedia entry on American Wire Gauge).
Now, I personally use a solid core 18 gauge wire for all my lights and would recommend you do the same. The cost difference between it and smaller cable is essentially negligible, and 18 gauge is about as big as you can go if you still want to be able to fit it into most COB holders or terminals. A larger cable like this reduces voltage drop and don’t have to worry too much about overloading it (unless you’re running a crazy amount of power on a single cable) since it’s capable of handling much more than the average COB system will be using.