With high quality displays and surround sound speaker systems becoming more and more affordable, it’s more common for people to run cable in the wall. It’s much cleaner and more attractive than running surface mounts or dangling the cable our in the open. However, in-wall installations can become complicated. For one thing, you have to consider where you are going to put your cable. Different installations by law require different ratings on the cable insulation. You need to make sure you buy wire with the correct insulation, without paying for more expensive insulation than you really need.

Most jurisdictions with have an electrical code use the NEC (National Electric Code), which was published by the National Fire Protection Association. Like most legal documents, the NEC is very large and confusing. We’re talking over 600 pages of legal text outlining every conceivable electrical installation their code requirements.

While it is long and confusing, the NEC is an important document that helps prevent hazards to human health and safety. They look at a few different categories including: tendency to start or perpetuate a fire, production of toxic fumes when exposed to fire, and electric shock.

Basically each rating classification designates the type of cable and where it can be used based on it's insulation jacket.

Riser and Plenum Spaces

Before we get into ratings there are two terms we should go over: riser and plenum. Riser refers to the space between one floor of a building and another. Plenum is a compartment to which one or more air ducts are connected that forms part of an air ventilation system. Cables usually require a special rating to be installed in these spaces, designated by the letters R (for riser) and P (for plenum). To learn more about plenum spaces check out this article.

NEC Cable Ratings

There are a bunch of different ratings under the NEC. Usually you can see the rating stamped on the cable jacket. Most of these ratings are suitable for in-wall installations in a residential home; however certain installations require a specific rating.