Conductors of ac and dc circuits, rated 600 volts, nominal, or less, shall be permitted to occupy the same equipment wiring enclosure if ___.
a. all conductors within the enclosure have an insulation rating equal to at least 600 volts
b. all conductors operating at different voltage levels within the enclosure are separated by a permanent barrier
c. all conductors have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure
d. each conductor has an ampacity equal to at least the maximum circuit current carried by each individual conductor within the enclosure