The requirements cover nonmetallic raceways and fittings. These products are for use as surface wiring systems in accordance with the National Electrical Code (NEC), NFPA 70. Raceways of the following thicknesses are to be considered as being intended to enclose circuitsoperating at potentials not exceeding 600 volts between conductors: All-nonmetallic raceways of any thickness and Raceways consisting of metal covers at least 0.040 inch (1.02 mm) thick nominal on nonmetallic bases. Raceways consisting of nonmetallic bases with thinner metal covers are to be considered as being intended for circuits operating at potentials lower than 300 volts between conductors.