Article 426

Fixed Outdoor Electric Deicing and Snow- Melting Equipment

Part I. General

1. Scope. The requirements of this article shall apply to electrically energized heating systems and the installation of these systems.
   1. Embedded. Embedded in driveways, walks, steps, and other areas.
   2. Exposed. Exposed on drainage systems, bridge structures, roofs, and other structures.
   
   Informational Note: For further information, see ANSI/IEEE515.1-2012, Standard for the Testing, Design, Installation and Mainte‐ nance of Electrical Resistance Trace Heating for Commercial Applica‐ tions.
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 gener‐ ated 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 an isolating trans‐ former. The pipe or rod shall be permitted to be embedded in the surface to be heated, or constitute the exposed compo‐ nents 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.Informational Note: Tubular heaters, strip heaters, heating cable, heating tape, and heating panels are examples of resist‐ ance heaters.Skin-Effect Heating System. A system in which heat is gener‐ ated on the inner surface of a ferromagnetic envelope embed‐ ded in or fastened to the surface to be heated.Informational Note: Typically, an electrically insulated conduc‐ tor is routed through and connected to the envelope at the other end. The envelope and the electrically insulated conduc‐ tor are connected to an ac voltage source from an isolating transformer.
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 according to Article 422.
4. Continuous Load. Fixed outdoor electric deicing and snow-melting equipment shall be considered a continuous load.

Part II. Installation

1. General. Equipment for outdoor electric deicing and snow melting shall be identified as being suitable for the follow‐ ing:
   1. The chemical, thermal, and physical environment
   2. Installation in accordance with the manufacturer’s draw‐ ings and instructions
2. Use. Electric heating equipment shall be installed in such a manner as to be afforded protection from physical damage.
3. 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.
4. Identification. The presence of outdoor electric deic‐ ing and snow-melting equipment shall be evident by the post‐ ing of appropriate caution signs or markings where clearly visible.
5. 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.

Part III. Resistance Heating Elements

1. Embedded Deicing and Snow-Melting Equipment.
   1. Watt Density. Panels or units shall not exceed 1300 watts/m2 (120 watts/ft2) of heated area.
   2. 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.
   3. Cover. Units, panels, or cables shall be installed as follows:
      1. On a substantial asphalt or masonry base at least 50 mm (2 in.) thick and have at least 38 mm (11∕2 in.) of asphalt or masonry applied over the units, panels, or cables; or
      2. They shall be permitted to be installed over other approved bases and embedded within 90 mm (31∕2 in.) of masonry or asphalt but not less than 38 mm (11∕2 in.) from the top surface; or
      3. Equipment that has been listed for other forms of instal‐ lation shall be installed only in the manner for which it has been identified.
   4. Secured. Cables, units, and panels shall be secured in place by frames or spreaders or other approved means while the masonry or asphalt finish is applied.
   5. Expansion and Contraction. Cables, units, and panels shall not be installed where they bridge expansion joints unless provision is made for expansion and contraction.
   ARTICLE 426 — FIXED OUTDOOR ELECTRIC DEICING AND SNOW-MELTING EQUIPMENT 426.43
2. Exposed Deicing and Snow-Melting Equipment.
   1. Secured. Heating element assemblies shall be secured to the surface being heated by approved means.
   2. Overtemperature. Where the heating element is not in direct contact with the surface being heated, the design of the heater assembly shall be such that its temperature limitations shall not be exceeded.
   3. Expansion and Contraction. Heating elements and assem‐ blies shall not be installed where they bridge expansion joints unless provision is made for expansion and contraction.
   4. Flexural Capability. Where installed on flexible struc‐ tures, the heating elements and assemblies shall have a flexural capability that is compatible with the structure.
3. Installation of Nonheating Leads for Embedded Equip‐ ment.
   1. Grounding Sheath or Braid. Nonheating leads having a grounding sheath or braid shall be permitted to be embedded in the masonry or asphalt in the same manner as the heating cable without additional physical protection.
   2. Raceways. All but 25 mm to 150 mm (1 in. to 6 in.) of nonheating leads not having a grounding sheath shall be enclosed in a rigid metal conduit, electrical metallic tubing, intermediate metal conduit, or other raceways within asphalt or masonry. The distance from the factory splice to raceway shall not be less than 25 mm (1 in.) or more than 150 mm (6 in.).
   3. Bushings. Insulating bushings shall be used in the asphalt or masonry where leads enter conduit or tubing.
   4. Expansion and Contraction. Leads shall be protected in expansion joints and where they emerge from masonry or asphalt by rigid conduit, electrical metallic tubing, intermedi‐ ate metal conduit, other raceways, or other approved means.
   5. Leads in Junction Boxes. Not less than 150 mm (6 in.) of free nonheating lead shall be within the junction box.
4. Installation of Nonheating Leads for Exposed Equip‐ ment.
   1. Nonheating Leads. Power supply nonheating leads (cold leads) for resistance elements shall be identified for the temperature encountered. Not less than 150 mm (6 in.) of nonheating leads shall be provided within the junction box. Preassembled factory-supplied and field-assembled nonheating leads on approved heaters shall be permitted to be shortened if the markings specified in 426.25 are retained.
   2. Protection. Nonheating power supply leads shall be enclosed in a rigid conduit, intermediate metal conduit, electri‐ cal metallic tubing, or other approved means.
5. Electrical Connection.
   1. Heating Element Connections. Electrical connections, other than factory connections of heating elements to nonheat‐ ing elements embedded in masonry or asphalt or on exposed surfaces, shall be made with insulated connectors identified for the use.
   2. Circuit Connections. Splices and terminations at the end of the nonheating leads, other than the heating element end, shall be installed in a box or fitting in accordance with 110.14 and 300.15.
6. Marking. Each factory-assembled heating unit shall be legibly marked within 75 mm (3 in.) of each end of the nonheating leads with the permanent identification symbol, catalog number, and ratings in volts and watts or in volts and amperes.
7. Corrosion Protection. Ferrous and nonferrous metal raceways, cable armor, cable sheaths, boxes, fittings, supports, and support hardware shall be permitted to be installed in concrete or in direct contact with the earth, or in areas subject to severe corrosive influences, where made of material suitable for the condition, or where provided with corrosion protection identified as suitable for the condition.
8. Grounding Braid or Sheath. Grounding means, such as copper braid, metal sheath, or other approved means, shall be provided as part of the heated section of the cable, panel, or unit.
9. Ground-Fault Protection of Equipment. Ground-fault protection of equipment shall be provided for fixed outdoor electric deicing and snow-melting equipment.

Part IV. Impedance Heating

1. Personnel Protection. Exposed elements of impe‐ dance heating systems shall be physically guarded, isolated, or thermally insulated with a weatherproof jacket to protect against contact by personnel in the area.
2. Isolation Transformer. An isolation transformer with a grounded shield between the primary and secondary windings shall be used to isolate the distribution system from the heating system.
3. Voltage Limitations. The secondary winding of the isolation transformer connected to the impedance heating elements shall not have an output voltage greater than 30 volts ac.
4. Induced Currents. All current-carrying components shall be installed in accordance with 300.20.
5. Grounding. An impedance heating system that is oper‐ ating at a voltage greater than 30 but not more than 80 shall be grounded at a designated point(s).

Part V. Skin-Effect Heating

1. Conductor Ampacity. The current through the electri‐ cally insulated conductor inside the ferromagnetic envelope shall be permitted to exceed the ampacity values shown in Arti‐ cle 310, provided it is identified as suitable for this use.
2. Pull Boxes. Where pull boxes are used, they shall be accessible without excavation by location in suitable vaults or abovegrade. Outdoor pull boxes shall be of watertight construction.
3. Single Conductor in Enclosure. The provisions of

300.20 shall not apply to the installation of a single conductor in a ferromagnetic envelope (metal enclosure).

1. Corrosion Protection. Ferromagnetic envelopes, ferrous or nonferrous metal raceways, boxes, fittings, supports, and support hardware shall be permitted to be installed in concrete or in direct contact with the earth, or in areas subjec‐
   ted to severe corrosive influences, where made of material suit‐ able for the condition, or where provided with corrosion protection identified as suitable for the condition. Corrosion protection shall maintain the original wall thickness of the ferromagnetic envelope.
2. Grounding. The ferromagnetic envelope shall be connected to an equipment grounding conductor at both ends; and, in addition, it shall be permitted to be connected to an equipment grounding conductor at intermediate points as required by its design.

The provisions of 250.30 shall not apply to the installation of skin-effect heating systems.

Informational Note: For grounding methods, see Article 250.

Part VI. Control and Protection

1. Disconnecting Means.
   1. Disconnection. All fixed outdoor deicing and snow- melting equipment shall be provided with a means for simulta‐ neous disconnection from all ungrounded conductors. Where readily accessible to the user of the equipment, the branch- circuit switch or circuit breaker shall be permitted to serve as the disconnecting means. The disconnecting means shall be of the indicating type and be capable of being locked in the open (off) position.
   2. Cord-and-Plug-Connected Equipment. The factory- installed attachment plug of cord-and-plug-connected equip‐ ment rated 20 amperes or less and 150 volts or less to ground shall be permitted to be the disconnecting means.
2. Controllers.

1. Temperature Controller with “Off” Position. Tempera‐ ture controlled switching devices that indicate an “off” position and that interrupt line current shall open all ungrounded conductors when the control device is in the “off” position. These devices shall not be permitted to serve as the disconnect‐ ing means unless they are lockable in accordance with 110.25.
2. Temperature Controller Without “Off” Position. Temper‐ ature controlled switching devices that do not have an “off” position shall not be required to open all ungrounded conduc‐ tors and shall not be permitted to serve as the disconnecting means.
3. Remote Temperature Controller. Remote controlled temperature-actuated devices shall not be required to meet the requirements of 426.51(A). These devices shall not be permit‐ ted to serve as the disconnecting means.
4. Combined Switching Devices. Switching devices consist‐ ing of combined temperature-actuated devices and manually controlled switches that serve both as the controller and the disconnecting means shall comply with all of the following conditions:

1. Open all ungrounded conductors when manually placed in the “off” position
2. Be so designed that the circuit cannot be energized auto‐ matically if the device has been manually placed in the “off” position
3. Be lockable in accordance with 110.25

426.54 Cord-and-Plug-Connected Deicing and Snow-Melting Equipment. Cord-and-plug-connected deicing and snow- melting equipment shall be listed.