The installation of service entrance conductors exceeding 1,000 volts ac, 1,500 volts dc, nominal, within a building or structure must be limited to the following methods: Galvanized rigid metal conduit, galvanized intermediate metal conduit, schedule 80 polyvinyl chloride conduit, metal-clad cable that is exposed for its entire length, cablebus, or busways. Exception: Wiring methods per NEC 235.402(B) shall be permitted for service conductors within a building or structure when customer owned overcurrent protection in accordance with NEC requirements is provided outside the building.