Every Wire Tells You What It Is
The printing stamped along an electrical cable is a complete spec sheet, and learning to read it tells you exactly what wire you are holding. Whether you are checking what is already in a wall or confirming a new roll, the legend on the jacket answers the key questions: what size, how many conductors, what type, and what it is rated for.
The Gauge and Conductor Count
The most prominent marking is a pair of numbers such as 12-2 or 14-3. The first number is the wire gauge in AWG, and the second is the count of insulated current-carrying conductors. So 12-2 is two insulated 12 AWG conductors, and 14-3 is three insulated 14 AWG conductors. The word WITH GROUND, or simply the letter G, means a bare equipment ground is also included, which is standard on residential cable.
The Cable Type
Next is the cable type, which tells you where it can be used. NM-B is standard dry-location Romex, UF-B is direct burial, THHN and THWN-2 are individual conductors for conduit, and SER is service entrance cable. Matching the type to the location is just as important as the gauge.
Voltage, Temperature, and Metal
The legend also shows the voltage rating, commonly 600V for building wire, and the temperature rating of the insulation, such as 90 degrees Celsius. It will indicate the conductor metal, with CU for copper or AL for aluminum. A UL listing mark confirms the cable was tested to safety standards.
Footage Markers
Most modern cable is printed with sequential footage markers every two feet. By reading the numbers at each end of what remains on a roll, you can tell how much wire you have used or have left without measuring it by hand. This is a handy way to track material on a job.
Jacket Color
For NM-B Romex, the jacket color is a quick gauge check: white for 14 AWG, yellow for 12 AWG, and orange for 10 AWG. This is an industry convention used by major brands, not a substitute for reading the printed gauge, but it speeds up identification on the job.
IB Lighting carries clearly marked Southwire and CerroMax by Cerrowire cable in our electrical wire and cable collection, with free freight plus free freight insurance on every order. Call (800) 674-9019 if you need help identifying the right wire for your project.