Consider the carrying capacity and the quantity of current the wire must carry when determining the gauge wire you want (measured in amperage or amps). The wire gauge is proportional to the number of amps that must be passed through it. The gauge of wire required can also be influenced by the distance the wire must travel. Larger wires are needed for longer distances.
The actual sizing of the wire depends on how it will be used. Most wiring jobs include support cables to distribute current along parallel paths in case one section fails. The more circuits you need, the larger the cable needs to be. If you plan to run your cable into confined spaces, like up walls or under floors, you will need smaller wires. Wires that small can be difficult to work with so they are usually only used for temporary work like testing equipment or mock-ups.
The first thing you should do is determine what kind of load you will be putting on the circuit. This will help you choose the correct size wire. Do not forget about voltage drops when choosing the right size wire. A 14 AWG copper wire can handle up to 140 amps before it starts to get hot. That's a lot of juice! A better choice would be to use 12 AWG wire if you can afford it. It will last longer and pose less risk of burning someone if there's a power surge.
Next, measure the length of the cable you want to use.
The wire gauge should be able to handle the maximum load current plus a 10% safety buffer. Positive and negative conductors should both be at least that gauge. It is OK for either to grow in size, but it will come at a higher expense. Don't become any smaller. A common mistake is to use only half the required number of wires to save money. If you're only using three-quarters of a circuit's normal load, then why not use four quarters instead? The answer is simple: power circuits need to be designed for the worst case scenario so they can handle the average load. If your house goes dark every time it rains, you'd better buy more wiring than you think you'll need.
The voltage drop across resistance is equal to IR. So, if you have a resistor between ground and line voltage, then V=IR. In other words, the higher the current, the hotter it gets. That means that as wires get longer, they also get hotter. And since heat always moves toward lower temperatures, that means that shorter wires are preferable if you want your cables to stay within safe operating parameters.
Cables are usually rated by their maximum load capacity before they must be replaced. This allows enough wire to be used so that it won't break under normal conditions. When installing cable, therefore, allow for high usage without replacement, as this avoids sudden costs upon installation of new cable.
Conversion of Wire Gauge
|Wire Number (Gauge)||A.W.G. or B&S (Inches)||A.W.G. Metric (MM)|
14-, 12-, 10-, 8-, 6-, and 2-gauge wire are common diameters. The amount of current that may safely run through the wire is determined by the wire's size. The ampacity of electrical current is tested, and each wire gauge has a maximum safe carrying capacity. For example, 12-gauge wire can carry up to 4 amps of current, while 14-gauge wire can carry up to 7 amps.
The best way to be sure you have the correct size wire for any project is to take the time to measure it first. Use string or tape to make sure the distance between markers on the wire equals or exceeds the height required by the application. If not, go down a size until you find one that will work. It's better to use too much wire than not enough!
When working with electricity, safety is paramount. Don't try to be a superhero and cut corners by using lower-quality wire or ignoring ampacity limits. An accident waiting to happen will most likely happen anyway if you're not paying attention. Do yourself and others around you a favor by using proper wiring practices every step of the way.