Surge Protective Device (SPD) : A device composed of any combination of linear or nonlinear circuit elements intended for limiting surge voltages on equipment by diverting or limiting surge current
NFPA 780 Standard for the Installation of Lightning Protection Systems, 2008 ed. http://www.uscg.mil/Petaluma/TPF/ET_SMS/Manuals/NF PA_780.pdf, (Std: Instll of Lightning Prot Sys - Amer) {347 NFC}