THHN500BK500 THHN 500 STR Black 500. Copper Conductors Are Primarily Used In Conduit and Cable Trays For Services, Feeders and Branch Circuits In Commercial or Industrial Applications As Specified In The National Electrical Code. Voltage For All Applications Is 600 Volts. Simpull THHN® Copper Conductors Are Designed to Be Installed Without Application Of A Pulling Lubricant.