In nonmetallic sheathed cable (NM) now purchased used for residential and commercial wiring, the outer sheathing color indicates the wire gauge or size and amperage rating of the wire within. However, older installed cable may not have this color coding.
Before about 2001, most NM cable had a white outer jacket, but since 2001, most NM-B cable has been jacketed with a vinyl outer insulation that is colored to identify it for both consumers and inspectors. This color coding of the wire sheath is strictly voluntary, but most manufacturers have now followed suit in adhering to the color scheme.
01 of 07
02 of 07
03 of 07
04 of 07
Black-sheathed cable is used for both 6- and 8-gauge wire. 8-gauge wire is rated for 45-amp circuits, while 6-gauge wire is capable of handling 60-amp circuits. The 6-gauge wire is better for a feeding a sub panel, an electric range, or a double oven, depending on the amperage rating listed on the appliance.
If you need black cable, make sure to read the sheathing and packaging carefully to determine if you are buying 6-or 8-gauge wire.Continue to 5 of 7 below.
05 of 07
Gray-colored sheathing is used to designate cable intended for underground installation. It has excellent water resistance and may also be rated for resistance to oil and sunlight. In this cable, the conductors are embedded in solid vinyl rather than running loosely inside the jacket.
Because the gray coding does not indicate wire size, read the packaging and jacket printing to make sure you are buying cable with the right wire gauge.
06 of 07
Outer Jacket Labeling
With all nonmetallic sheathed cable, the outer jacket is labeled with letters that show how many insulated wires are concealed within the sheathing. This wire count does not, however, include the uninsulated bare copper wire that is used as a grounding wire. For instance, if the cable lists 12-2 WG, it means there are two insulated 12-gauge wires (a black and a white wire), plus a ground wire. If the label says 12-3, this is a three-conductor (red, black, and white), 12-gauge cable with a bare copper ground wire included.
07 of 07
Color Coding on Individual Conductors
The wires inside a sheathed cable will also have plastic insulation that is color-coded for easy recognition. All cables will have a white insulated wire and a black insulated wire; these identify the neutral and the hot wires, respectively.
The bare copper wire in the cable is the ground wire. (In rare instances, you might find cable in which the ground wire is covered with green insulation—green is the color designated for ground wires.)
In a three-wire cable, there will be a red wire in addition to the white and black wires. Red is also designated as a hot color.