Why do SPD manufacturers no longer describe their products as TVSS?

TVSS devices have always belonged to a larger family of surge suppression devices known as SPDs (Surge Protective Devices). Beginning with UL 1449 3rd Edition and the 2008 National Electrical Code, the term “SPD” has formally replaced the terms “TVSS” and “Secondary Surge Arrester”. SPDs are now classified as Type 1, Type 2, Type 3 or Type 4 and are selected based on application and the location where they are to be used. With the recent changes in terminology by UL and the NEC, there are no longer any standards organizations that use the term TVSS, as IEEE®, IEC® and NEMAhave been using the term “SPD” for many years.