Hermetically Sealed or Factory Sealed

The 2014 edition of the National Electrical Code (NEC) [Sec. 500.7(J)] describes "hermetically sealed" as one of the protection techniques allowed in classified areas. In Sec. 500.2, the term "hermetically sealed" is defined as: "Equipment sealed against the entrance of external atmosphere where the seal is made by fusion, for example, soldering, brazing, welding, or the fusion of glass to metal." This definition is important because it specifically states how the containment of the equipment, such as contacts, is achieved.

...