Structure, Metal-Framed : A structure with electrically continuous structural members of sufficient size to provide an electrical path equivalent to that of lightning conductors
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}