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Knowing the basic wire types is essential to almost any electrical project around the house. When you're installing new wiring, for example, choosing the right wire or cable is half the battle. And when you’re examining existing wiring in your home, identifying the wire type can tell you a lot about the circuit the wiring belongs to—for example, when you open a junction box and need to determine which wires go where. Wiring for modern homes is quite standard, and most homes built after the mid-1960s have similar types of wiring. Any new electrical installation requires new wiring that conforms to local building codes.
Before you take on your next home wiring project, arm yourself with basic information about the electrical cable and wiring that you’re likely to see.
Here are some common types of home electrical wire.
Cable vs. Wire
People often use these terms interchangeably, but there’s a difference:

Cable is an assembly of two or more wires in a single jacket.
Wires are the individual insulated or bare conductors inside the jacket.
Wire Gauge
Wires come in different sizes/gauges to work with the amperage of the circuit in which they’re used. It’s counterintuitive, but the larger the number, the smaller the wire.

The most common sizes you’ll find in residential work are 14-gauge and 12-gauge. Larger appliances such as electric stoves, electric water heaters, electric dryers and central air units will often use 10-, 8- or even 6-gauge wire.
Cable by the Numbers
An electrical cable is classified by two numbers separated by a hyphen, such as 14-2. The first number denotes the conductor’s gauge; the second denotes the number of conductors inside the cable.

For instance, 14-2 has two 14-gauge conductors: a hot and a neutral. This cable also contains a bare copper wire as the ground. Individual conductors are also color-coded, which tells you their purpose in the circuit.
Outer Sheath Color Coding
The color of a cable’s outer sheath tells you the gauge of the wire inside the sheath as well as the amperage rating for the circuit.

WHITE = 14-gauge wire, 15-amp circuit

YELLOW = 12-gauge wire, 20-amp circuit

ORANGE = 10-gauge wire, 30-amp circuit

BLACK = 8- or 6-gauge wire, 45- or 60-amp circuits. Check sheath labeling for gauge and circuit specifics.

GRAY = Underground cable. Since all UF (underground feeder) cable is gray, check the sheath labeling for gauge and circuit specifics.
NM-B – Nonmetallic Cable
This is the most common type of electrical cable in homes built since the mid-’60s. “Nonmetallic” simply means that the outer jacket is not metal. It’s often referred to as Romex, which is a brand name. Typically, NM-B cable has either two conductors and a ground, or three conductors and a ground. The conductors are individually insulated, wrapped in paper and sheathed in plastic. Ground wires are either bare copper or insulated in green.

14-2 Used for general lighting and receptacle circuits. 15-amp circuit maximum.

14-3 Used for three-way switches and split receptacle circuits. 15-amp circuit maximum.

12-2 Used for 20-amp kitchen, bathroom, laundry and garage receptacles; 230-volt heating circuits up to 3,700 watts; and 115-volt circuits up to 1,800 watts. Can be used anywhere in place of 14-2.

12-3 Same uses as 12-2, with the addition of three-way switches and split receptacle circuits.