These supports shall have maximum center-to-center spacing of 36 inches for horizontal bus, and 18 inches for vertical bus. Insulating supports shall be fabricated from injection molded glass reinforced polymer. These are practical values, often higher than the IEC minimums, and depend. If you can place bare conductors 1/2" apart and meet the test requirements for 15kV equipment, that is fine. And before you conclude that I'm being ridiculous, remember that we do this every day in vacuum interrupters. This document supersedes the following documents, all copies of which should be destroyed. 0-inch. This article is for manufacturing, testing of non-segregated Bus Bars and Bus Ducts rated 600 V to 35 kV as per international standard ANSI C37.