Finish Ratings of Gypsum Wallboards

The term finish rating is used in NFPA 70, National Electrical Code (NEC)¹ to describe the required performance of finish materials installed as thermal barriers for electrical nonmetallic tubing. Finish rating data is most commonly associated with assemblies containing combustible wood framing, although the definition has also been extended to assemblies with noncombustible metal framing. To date, however, very little finish rating data has been available for common finish materials installed over metal framing. To supplement the available information, finish rating tests were conducted on identical wall sections finished with standard 1/2 gypsum wallboard from five different manufacturers, constructed with metal and wood stud framing. All 10 assemblies tested demonstrated finish ratings of 15 minutes or more.