Understanding The Terminology: Listing, Recognition, And Classification

Interpreting the meaning of the National Electrical Code (NEC) can confound even the seasoned electrician from time to time. In studying the NEC, everyone should start with Article 100 – Definitions. Today I want to take a closer look at a couple of those definitions-"Labeled," and "Listed." In straightforward language what, these two definitions tell us is that anything we use when installing an electrical system must be approved by an organization that is acceptable to the authority having jurisdiction in your area. In the United States, the accepted organization is the Underwriters Laboratories (UL) but the UL adds to the confusion by classifying equipment and materials by using three different terms-"Listed," "Recognition," and "Classification." These three terms have distinctly different meanings.

Listing, Recognition, And Classification -Are Not Interchangeable
The Underwriters Laboratory requires that equipment and materials meet certain standards for each of these categories. Understanding how these UL standards differ and what they mean to you as an electrician is a vital part of every electrician’s education. Being able to identify them by the symbols used by the UL is essential to installing an electrical system that will pass the inspection by the Authority Having Jurisdiction (AHJ).

Underwriters Listed
Everyone is familiar with the symbols indicating that a product is UL Listed, the familiar trademark, the encircled "UL." This trademark appears on complete products that are safe to use right out of the box. It appears on everything from a portable electric drill to a complete computer system. Products like computer system may or may not be UL Listed because "Listing" is voluntary. The manufacturer can submit his product for testing and UL Listing. This is to the manufacturer’s advantage because it lifts the responsibility for the safety of his product off him. A builder of custom computers does not have to have his designs listed. Products do not have to be listed as long as they are assembled using UL Recognized components.

Underwriter Laboratory Recognized Components
The UL tests and recognizes components like light switches, duplex receptacles, circuit breakers, and computer power supplies. "Recognized" components are safe in and of themselves, but that does not mean that they cannot be used in such a way that they cannot become unsafe. A computer power supply that is UL Recognized as being safe can become a potential fire hazard when installed in an overcrowded computer case. Underwrite Laboratory’s Recognized components are indicated by a special symbol, a slanted "U" and a slanted, reversed "R" used together. Because of the potential dangers of the misapplication of UL Recognized components, it behooves the manufacturer of products to apply for an UL Listing, and it behooves to the consumer to buy only products that carry a UL Listing.

Underwriters Laboratory Classification
This term is used by the UL mostly in relationship to industrial and commercial equipment and materials. Industrial and commercial equipment that carries UL "Classification" has no symbol as UL Listed and Recognized products have but they carry the Underwriters Laboratory’s name and a brief statement attesting to its "Classification."