The circuit sizes of Romex® cable are all broken down into colored jackets based on their size. The 14 AWG cables are gray, the 12 AWG cables are yellow and the 10 AWG cables are orange. The balance of larger sizes come in a black outer jacket only.
The yellow jacket helps contractors, installers and electricians understand the gauge size before having to take the connection apart. The size and conductor count is printed on the jacket when it’s manufactured but often times the writing will start to fade making it difficult to see the AWG size. That’s why it makes it easier on installers to be able to see what size of Romex® they will need to complete a job.
The yellow 12 AWG Romex® cables come in a 2 or 3 conductor only. Each of those cables will come with an additional ground wire. The colors of the conductor will be either: black and white or black, white and red. The ground wire is additional and comes without insulation in a solid copper strand.
Romex® cables come in a round version which commonly gets confused with UFB cables. UFB is an underground feeder cable that’s an upgrade to NMB cable and it’s flat due to how it’s manufactured. Instead of the PVC jacket wrapping around all of the conductors it wraps around each individual conductor for added protection. The extra protection allows the cable to be used outdoors and directly underground without conduit.
The underground cables aren’t color coded like Romex® because they will be underground anyways. There isn’t a need to have the jacket colored. The conductors are color coded the same as NMB cable with black, white and red THHN wires. THHN can be used on its own if you want to run 2 or 3 individual wires rather than a bundled cable. It’s all up to the installer’s preferences. Sometimes you’ll find a better deal on 3 individual wires compared to buying the full cable with a jacket. Just remember to buy a green THHN wire for the ground instead of a bare copper wire because THHN can be used outdoors and in conduit where bare copper cannot.
Speak with your supplier about your application so they can find the cheapest option for you. They will make sure it has all of the approvals needed for your particular situation and make sure that you’re not buying more than you need.
WesBell Electronics is a wire and cable distributor that stocks Romex® and all types of hook up wire. Romex® 12 3 wire is a common item that we have in our inventory in 2 or 3 conductor with an additional ground wire included.