I. General
according to Article 422.
426.4 Continuous Load. Fixed outdoor electric deicing and snow-melting equipment shall be considered as a continuous load.
II. Installation
426.10 General. Equipment for outdoor electric deicing and snow melting shall be identified as being suitable for the following:
426.1 Scope. The requirements of this article shall apply to electrically energized heating systems and the installation of these systems.
(A) Embedded. Embedded in driveways, walks, steps, and other areas.
(B) Exposed. Exposed on drainage systems, bridge structures, roofs, and other structures.
426.2 Definitions.
Heating System. A complete system consisting of components such as heating elements, fastening devices, nonheating circuit wiring, leads, temperature controllers, safety signs, junction boxes, raceways, and fittings.
Impedance Heating System. A system in which heat is generated in a pipe or rod, or combination of pipes and rods, by causing current to flow through the pipe or rod by direct connection to an ac voltage source from a dual-winding transformer. The pipe or rod shall be permitted to be embedded in the surface to be heated, or constitute the exposed components to be heated.
Resistance Heating Element. A specific separate element to generate heat that is embedded in or fastened to the surface to be heated.
FPN: Tubular heaters, strip heaters, heating cable, heating tape, and heating panels are examples of resistance heaters.
Skin-Effect Heating System. A system in which heat is generated on the inner surface of a ferromagnetic envelope embedded in or fastened to the surface to be heated.
FPN: Typically, an electrically insulated conductor is routed through and connected to the envelope at the other end. The envelope and the electrically insulated conductor are connected to an ac voltage source from a dual-winding transformer.
426.3 Application of Other Articles. Cord-and-plug- connected fixed outdoor electric deicing and snow- melting equipment intended for specific use and identified as suitable for this use shall be installed
(1) The chemical, thermal, and physical environment
(2) Installation in accordance with the manufacturer's drawings and instructions
426.11 Use. Electric heating equipment shall be installed in such a manner as to be afforded protection from physical damage.
426.12 Thermal Protection. External surfaces of outdoor electric deicing and snow-melting equipment that operate at temperatures exceeding 60°C (140°F) shall be physically guarded, isolated, or thermally insulated to protect against contact by personnel in the area.
426.13 Identification. The presence of outdoor electric de-icing and snow-melting equipment shall be evident by the posting of appropriate caution signs or markings where clearly visible.
426.14 Special Permission. Fixed outdoor deicing and snow-melting equipment employing methods of construction or installation other than covered by this article shall be permitted only by special permission.
III. Resistance Heating Elements
426.20 Embedded Deicing and Snow-Melting Equipment
(A) Watt Density. Panels or units shall not exceed 1300 watts/m 2 (120 watts/ft 2) of heated area.
(B) Spacing. The spacing between adjacent cable runs is dependent upon the rating of the cable and shall be not less than 25 mm (1 in.) on centers.
(C) Cover. Units, panels, or cables shall be installed as follows:
(1) On a