12/3 wire for new construction

Question

My friend gave me two spools of 12/3 wire which are considered flexible (it has a round black coating that has -40 C to 90 C rating printed on the wire). I was wondering if I can use this wire for a new construction or if I should use the flat yellow coated 12/3 wire which is most commonly used.

Answer

No!

Since you are obviously not an electrician, I will endeavor to explain so that you and other persons at your skill level will perhaps realize that electrical wiring is not something you take up on a whim without extensive study and training. If you were to look into previous answers to some questions, you will discover that I have a personal nemesis, "Handy Jack."

"Handy Jack" is my less than affectionate moniker for the representative of that class of the great unwashed who think that they have "discovered" a newer simpler solution to an electrical condition that is so much more reasonable than the process followed by the literally millions of obvious idiots working in the electrical trades, including construction, engineering, design and manufacturing and possessing the combined knowledge derived from tens, if not hundreds, of BILLIONS [I am an electrician, not a mathematician. There are roughly 600,000 electricians who clock 2,000 to 3,000 working hours each year and have, in increasing numbers, for the past 100 years!] of hours of exposure to, and contemplation of, the safe and useful application of electrical energy as we understand it. Jack, of course, can see clearly where we have all overlooked the apparent, simple solution....

Btw, Handy Jack also does plumbing, carpentry, roofing and siding, replacement window installation, auto repairs and brain surgery.

All equipment suitable for use in electrical installations has a definitive design purpose and is inspected by third party organizations, like Underwriters Laboratories. What they do is test materials to determine if it is manufactured according to the listing and labeling it carries. In that listing and labeling, the manufacturer identifies what the material may be used for and how it is to be installed or used. The materials for uses are defined by standards institutes like ANSI and their characteristics are identified in other standards like the National Electrical Code.

Now to YOUR question! The flat yellow "12/3" wire you describe is actually 12/2 non-metallic sheathed cable [NEC Article 334] with ground. It is actually considered a 2 conductor cable, because the bare wire can only be used for grounding purposes. It is suitable for certain types of construction under limited conditions. The round black cable you describe is flexible cord [NEC Article 400]. According to the NEC, there are very clear allowed uses of flexible cord [NEC Article 400.7] and very clearly delineated uses not permitted [NEC Article 400.8]. Use of flexible cord as a wiring method instead of non-metallic sheathed cable or other suitable means is strictly forbidden.

Lack of this minimal knowledge mandates that I recommend that you hire an electrician for your project.