The Rome Wire Company developed an insulated electrical building wire called Romex in 1922. In 1927, General Cable acquired the Rome Wire Company and the Romex brand until Southwire purchased General Cable's building wire division in 2001.
Romex wire is available in several configurations to suit specific residential and light commercial electrical building applications. The 10, 12, and 14 gauge wire (10 gauge being the thickest) in two and three conductor configurations are standard.
The 12 and 14 gauge Romex is used in the majority of home and and commercial electrical applications, while 10 gauge is used primarily for heavier commercial and light industrial electrical loads, such as those required for commercial-grade appliances and machinery. The number of conductor wires does not include the ground wire.
Heavier gauge Romex is used in high voltage industrial and commercial applications.
External Wire Identification
Romex wire can be identified by the Romex brand name, gauge, and number of internal conductor wires stamped on the outer insulation. For standard Romex used in residential and commercial projects, color-coded exterior insulation will assist in determining the cable type.
White is used to identify 14 gauge 2 and 3 conductor wire (14/2 or 14/3), yellow is used for 12 gauge 2 and 3 conductor wire (12/2 or 12/3), and orange is used for 10 gauge 2 and 3 conductor wire (10/2 or 10/3). Gray outer insulation is used to identify 2, 4, 6 and 8 gauge industrial-grade Romex.
Internal Wire Identification
National Electrical Codes determine the insulation color of electrical building wire. Ground wires are bare, and have no insulation.
Positive "hot" wires are either black or red, and the neutral wire is white. The two "hot" wire insulation colors (black and red) are used for 3 conductor cable, when two positive wires are required for certain electrical connections.
For 2 conductor cable, black is the standard identification color for the positive wire.
Romex brand cable is intended for indoor applications in dry areas only, and is not suitable for outdoor or underground use. Most electrical wiring jobs must be done in accordance with local, state, and national laws and published standards (codes).
Although some electrical wiring projects are easy, it is necessary to check with your local building inspector to determine which jobs are legal to perform without employing a licensed electrician. Aside from the dangers of electrocution, improper wiring can cause house fires or damage to electrical appliances and fixtures.