When choosing the correct electrical wire, it's important to consider what the wire is feeding, the wire gauge and the wire capacity, states About.com. In general, smaller gauge wires have higher ampacity, which is the maximum amount of electrical current the wire can handle without sustaining damage.
The most commonly used wire gauges are 10, 12 and 14, according to Home Depot. Ten-gauge wire carries a maximum of 30 amps, with a maximum wattage load of 2,880 to 5,760 watts. It is commonly used to feed large appliances, such as a dryer or a window air conditioner. Primarily used in residential applications, 12-gauge wire can carry up to 20 amps and is used to feed light fixtures, receptacles and small appliances, such as microwaves. Fourteen-gauge wire is capable of carrying up to 15 amps and is usually used to carry electricity to lighting and receptacles.
Larger wire sizes, which have a smaller wire gauge, are used to supply power to large appliances, furnaces, service panels and sub panels, states About.com. Before beginning a wiring project, consulting a building inspector and obtaining the appropriate permits is recommended, states Home Depot. After the work is finished, it's best to have it inspected for safety and compliance with local codes.