SOUND-RECORDING AND SIMILAR EQUIPMENT 70-669

Exception No. 1: Special permission may be granted for the installation of two 2-conductor lead-covered cables in ³/₄-inch conduit or tubing, provided the cross-sectional area of each cable does not exceed 11 square inch (70.97 mm 2 ). Exception No. 2: Special permission may be granted for the installation of two 2-conductor No. 19 lead-covered cables in ¹/₂-inch conduit or tubing, provided the sum of the cross-sectional areas of the cables does not exceed 32 percent of the internal cross-sectional area of the conduit or tubing. 640-4. Wireways and Auxiliary Gutters. Wireways shall comply with the requirements of Article 362, and auxiliary gutters shall comply with the requirements of Article 374. Exception: Where used for sound-recording and reproduction, the following shall be complied with: a. Conductors in wireways or gutters shall not fill the raceway to more than 75 percent of its depth. b. Where the cover of auxiliary gutters is flush with the flooring and is subject to the moving of heavy objects, it shall be of steel at least ¹/₄ inch (6.35 mm) in thickness; where not subject to moving of heavy objects, as in the rear of patch or other equipment panels, the cover shall be at least No. 10 MSG. c. Wireways shall be permitted in concealed places, provided they are run in a straight line between outlets or junction boxes. Covers of boxes shall be accessible. Edges of metal shall be rounded at outlet or junction boxes and all rough projections smoothed to prevent abrasion of insulation or conductors. d. Wireways and auxiliary gutters shall be grounded and bonded in accordance with the requirements of Article 250. Where the wireway or auxiliary gutter does not contain power-supply wires, the equipment grounding conductor shall not be required to be larger than No. 14 copper or its equivalent. Where the wireway or auxiliary gutter contains powersupply wires, the equipment grounding conductor shall not be smaller than specified in Section 250-95. 640-5. Conductors. Amplifier output circuits carrying audio-program signals of 70 volts or less and whose open-circuit voltage will not exceed 100 volts shall be permitted to employ Class 2 or Class 3 wiring as covered in