FIXED ELECTRIC SPACE HEATING EQUIPMENT 70-367

Exception: Cables identified to be secured at intervals not to exceed 6 feet (1.83 m). (g) Dry Board Installations. In dry board installations, the entire ceiling below the heating cable shall be covered with gypsum board not exceeding ½ inch (12.7 mm) thickness. The void between the upper layer of gypsum board, plaster lath, or other fire-resistant material and the surface layer of gypsum board shall be completely filled with thermally conductive, nonshrinking plaster or other approved material or equivalent thermal conductivity. (h) Free from Contact with Conductive Surfaces. Cables shall be kept free from contact with metal or other electrically conductive surfaces. (i) Joists. In dry board applications, cable shall be installed parallel to the joist, leaving a clear space centered under the joist of 2½ inches (64 mm) (width) between centers of adjacent runs of cable. A surface 1 layer of gypsum board shall be mounted so that the nails or other fasteners do not pierce the heating cable. (j) Crossing Joists. Cables shall cross joists only at the ends of the room. Exception: Where the cable is required to cross joists elsewhere in order to satisfy the manufacturer's instructions that the installer avoid placing the cable too close to ceiling penetrations and light fixtures. 424-42. Finished Ceilings. Finished ceilings shall not be covered with decorative panels or beams constructed of materials that have thermal insulating properties, such as wood, fiber, or plastic. Finished ceilings shall be permitted to be covered with paint, wallpaper, or other approved surface finishes. 424-43. Installation of Nonheating Leads of Cables. (a) Free Nonheating Leads. Free nonheating leads of cables shall be installed in accordance with approved wiring methods from the junction box to a location within the ceiling. Such installations shall be permitted to be single conductors in approved raceways, single or multiconductor Type UF, Type NMC, Type MI, or other approved conductors. (b) Leads in Junction Box. Not less than 6 inches (152 mm) of free nonheating lead shall be within the junction box. The marking of the leads shall be visible in the junction box. (c) Excess Leads. Excess leads of heating cables shall not be cut but shall be secured to the underside of the ceiling and embedded in plaster or other approved material, leaving only a length sufficient to reach the junction box with not less than 6 inches (152 mm) of free lead within the box. 424-44. Installation of Cables in Concrete or Poured Masonry Floors. (a) Watts per Linear Foot. Heating cables shall not exceed 16½ watts per linear foot (305 mm) of cable. (b) Spacing Between Adjacent Runs. The spacing between adjacent runs of cable shall not be less than 1 inch (25.4 mm) on centers. 70-368 NATIONAL ELECTRICAL CODE (c) Secured in Place. Cables shall be secured in place by nonmetallic frames or spreaders or other approved means while the concrete or other finish is applied. Cables shall not be installed where they bridge expansion joints unless protected from expansion and contraction. (d) Spacings Between Heating Cable and Metal Embedded in the Floor. Spacings shall be maintained between the heating cable and metal embedded in the floor. Exception: Grounded metal-clad cable shall be permitted to be in contact with metal embedded in the floor. (e) Leads Protected. Leads shall be protected where they leave the floor by rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, electrical metallic tubing, or by other approved means. (f) Bushings or Approved Fittings. Bushings or approved fittings shall be used where the leads emerge within the floor slab. 424-45. Inspection and Tests. Cable installations shall be made with due care to prevent damage to the cable assembly and shall be inspected and approved before cables are covered or concealed. F. Duct Heaters 424-57. General. Part F shall apply to any heater mounted in the air stream of a forced-air system where the air-moving unit is not provided as an integral part of the equipment. 424-58. Identification. Heaters installed in an air duct shall be identified as suitable for the installation. 424-59. Airflow. Means shall be provided to assure uniform and adequate airflow over the face of the heater in accordance with the manufacturer's instructions. (FPN): Heaters installed within 4 feet (1.22 m) of the outlet of an air-moving device, heat pump, air conditioner, elbows, baffle plates, or other obstructions in duct work may require turning vanes, pressure plates, or other devices on the inlet side of the duct heater to assure an even distribution of air over the face of the heater. 424-60. Elevated Inlet Temperature. Duct heaters intended for use with elevated inlet air temperature shall be identified as suitable for use at the elevated temperatures. 424-61. Installation of Duct Heaters with Heat Pumps and Air Conditioners. Heat pumps and air conditioners having duct heaters closer than 4 feet (1.22 m) to the heat pump or air conditioner shall have both the duct heater and heat pump or air conditioner identified as suitable for such installation and so marked. 424-62. Condensation. Duct heaters used with air conditioners or other air-cooling equipment that may result in condensation of moisture shall be identified as suitable for use with air conditioners.