- What is the amount of current required for the lights?
- What are the conditions the wire will be used in or with? (water, UV exposure, temperature range, how much flex will it be exposed to)
- Cost - not only for the wire itself but also the connectors used with it.
- Easy of use (soldering, crimping, etc)
First, lets start off with the most important function of any wire - it's ability to carry power. The primary method of expressing power carrying ability of a wire is in amps. But...you need to look at the voltage also. For example, a wire rated to carry 1 amp of power (it doesn't matter is the power is DC or AC):
- 1 amp at 5 volts is 5 watts (Current or amps * Voltage = Watts)
- 1 amp at 12 volts is 12 watts
- 1 amp at 120 volts 120 watts
So, how to do you know how much current (or amps) a wire can handle? Well, it's complicated and at the end of this article we will show you the "real world" method to determine what wire you need to use. There are a number of factors that go into the calculation - including material type (tin, aluminum, copper), design (stranded vs solid wire), the diameter of the wire (gauge or in the US, AWG), the temperature the wire is exposed to, how many wires are bundled together and the insulating material. You can start with charts, such as this one that give you a rough idea of how much a SINGLE wire can carry - remember that there are always two wires required for AC and DC wiring systems. When you look at a chart you want to find the AWG (American Wire Gauge) or gauge. How do you know what gauge the cable is? Well, it's complicated also for the following reasons:
- Some vendors lie about the gauge of cable - this is very common for wiring sourced from China. This is most common with wiring used in RGB lights.
- The charts most often assume you are using solid copper - the best possible (short of gold and silver) conductor of power but often due to cost reasons, you may have tin wire plated in copper or aluminum wire plated in copper or some other variation, which renders the tables invalid.
Conditions The Wire is Used In
There is no one perfect wire because the conditions that each project it is used in vary. For example, one person may be permanently installing lighting onto their house and does not have intentions to remove it. In that case, issues of UV exposure (which breaks down the insulation on the cable) and temperature exposure become important factors. In this case you might also consider using a solid wire as opposed to a stranded wire as there will not be much future movement (and thus breakage) of the wire. For installations in very cold regions, the insulation material is an important consideration as common insulation's are made from vinyl which doesn't function well in low temperatures.
So, when selecting cable, consider how the cable will be used and select a cable that meets those specific environmental issues.
Of course a big factor in cable selection is cost. The major cost in any cable is the wire, which is most often copper. You don't want to select a cable that has conductors that are too thin and thus unable to carry sufficient current but you don't want to have overkill as this results in higher costs, heavier cable and often less flexibility. Also keep in mind that cable cost is also a function of the quality of the insulation, so if you cheap out on a cable that doesn't have UV resistance and the cable has to be replaced after two seasons (along with all the associated soldering and connections), you may not have saved that much in the long term.
There is always a "right" cable for every need out there in the market, though often those "special" cables are so expensive that the "right" cable can't be used. So after determining what gauge and insulation that is required, see what vendors carry that cable. Often moving to a more "standard" cable, such as in the case of CAT5, results in many more vendors, greater competition and as a result, lower costs and higher availability. So, don't rule out a cable that is close to the specs you need.
Ease of Use
This is one of the least considered factors in cable selection. Easy of use includes a variety of issues, such as:
- Can the cable be purchased with pre-attached and tested connectors? This is common with CAT5 and SPT cables which are standardized in wiring, color and design.
- How easy is it to attach connectors? Some wire can be very hard to work with due to the small gauge, multiple layers of insulation, strain reliefs or other factors. Having to attach connectors to each cable, correctly (to prevent possible mis-wiring related damage) can often take a considerable period of time depending on the number of cables you need.
- What types of connectors can be used and do they meet your needs? CAT5, for example, is ubiquitous and has many types of splitters / combiners, connectors (female / male, etc), waterproof and non-waterproof and more. If your design calls for direct attached cable, such as screw terminals, is the wire strong enough to handle multiple screw downs on it?
- Connector costs is one of the biggest factors. Usually in most systems you will have a connector based system for hooking up elements as they are, in the Holiday Lighting world, temporary in nature. So, while a spool of cable might be cheap up front, if it requires expensive connectors, the overall cost of that connection method goes up and the connectors could be more expensive than the cable itself. Be sure to think end-to-end on what you need from your connector - does it need to be waterproof or just water resistant? Does it matter if the connection is water resistant at all (such as the case with SPT cord.) Don't spend money on waterproofing connections that don't benefit from it.
So, I've discussed a variety of the issues you should consider on how to select a wire or more specifically, a wiring "system" - how does this work in the real world?
Let's say that you want to hookup four flood lights to a single controller. We will be using 100ft of cable between the power supply and each flood, resulting in a total of 500ft of cable between the start (power supply/controller) and the last flood. What cable do you need and what factors would you consider? They are: