what is spds
What Are SPDs. A surge protective device (SPD) is a protective device for limiting transient voltages by diverting or limiting surge current and is capable of repeating these functions as specified. SPDs were previously known as Transient Voltage Surge Suppressors (TVSS) or secondary surge arrestors (SSA). Secondary surge arrestor is a legacy term (often used by utilities) and is used most commonly for a device that has not been certified to ANSI/UL 1449. In 2009, after the adoption of ANSI/UL 1449 (3rd Edition), the term Transient Voltage Surge Suppressor was replaced by Surge Protective Device.