10.5 Deicing, Snow Melting, Pipeline and Vessel Heating

Why These Two Articles Matter in Alaska

Few jurisdictions apply Articles 426 and 427 as heavily as Alaska does. Roof and gutter deicing, ramp and walkway snow melting, freeze protection on water and fire-protection piping, and process heat tracing on fuel and glycol lines are routine work. Both articles share a structure and both hinge on ground-fault protection of equipment.

Article 426 — Deicing and Snow Melting

426.4 Continuous Load. Fixed outdoor electric deicing and snow-melting equipment shall be considered a continuous load. Branch-circuit conductors and the overcurrent device are therefore sized at 125 percent of the load under 210.19(A)(1) and 210.20(A).

426.10 General. Equipment for outdoor electric deicing and snow melting shall be identified as being suitable for the following: the chemical, thermal, and physical environment; and installation in accordance with the manufacturer's drawings and instructions.

426.11 Use. Equipment shall be installed in such a manner that it will be protected from physical damage.

426.12 Thermal Protection. External surfaces of outdoor electric deicing and snow-melting equipment that operate at temperatures exceeding 60 degrees C (140 degrees F) shall be physically guarded, isolated, or thermally insulated to protect against contact by personnel in the area.

426.13 Identification. The presence of electric deicing and snow-melting equipment shall be evident by the posting of appropriate caution signs or markings where clearly visible.

426.14 Special Permission. Fixed electric deicing and snow-melting equipment for other than these described uses shall be permitted only by special permission.

426.20 Embedded Deicing and Snow-Melting Equipment. (A) Heating element assemblies shall be installed on a substantial asphalt or masonry base at least 2 inches (50 mm) thick and have at least 1.5 inches of asphalt or masonry applied over the units; or they shall be permitted to be installed over the top of existing asphalt or masonry, provided they are covered with at least 1.5 inches of asphalt or masonry. (B) Units shall be secured in place while the masonry or asphalt finish is applied. (C) Where installed in concrete, cinder fill, or other permanent forms of construction, the units shall not be subject to physical damage. (D) Units shall be installed to provide effective heat transfer to the area to be heated. (E) Cables shall be spaced not closer than 1 inch (25 mm) on centers, providing not more than 120 watts per square foot of heated area. (F) Cables shall not cross over themselves.

426.21 Heating Cable Installation. Cables shall be installed in accordance with the manufacturer's instructions and 426.20 through 426.24.

426.22 Resistance Heating Elements and 426.23 Nonheating Leads cover terminations and lead installation. 426.24 Electrical Connection requires nonheating leads to be attached to the cable using a factory-assembled splice.

The Key Rule — 426.28

426.28 Ground-Fault Protection of Equipment. Ground-fault protection of equipment shall be provided for fixed outdoor electric deicing and snow-melting equipment, other than equipment that employs mineral-insulated, metal-sheathed cable embedded in a noncombustible medium.

Read this precisely. It requires ground-fault protection of equipment (GFPE) — not a Class A GFCI. GFPE devices are typically listed at a 30-milliampere trip level for heating applications, which is far above the 4-to-6-milliampere Class A range but far below a conventional overcurrent device. The distinction is deliberate: a long heat-trace circuit inherently leaks more than 6 milliamperes, and requiring a Class A device would produce constant nuisance tripping while a GFPE device still catches the sheath damage that starts fires.

The exception is narrow: mineral-insulated metal-sheathed cable embedded in a noncombustible medium.

210.8(A)(3) Exception ties back to this: the outdoor GFCI requirement for dwelling receptacles has an exception for receptacles supplying only snow-melting or deicing equipment on a dedicated branch circuit installed in accordance with Part III of Article 426. That exception is specific — it does not exempt general-purpose outdoor receptacles, and it does not exempt engine block heater outlets.

426.50 Disconnecting Means. All fixed outdoor deicing and snow-melting equipment shall be provided with a means for simultaneous 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 provided with a positive lockout in the off position.

426.51 requires controllers and thermostats to be either rated for the load or have a horsepower rating, and to be marked.

Article 427 — Pipeline and Vessel Heating

427.4 Continuous Load. Fixed electric heating equipment for pipelines and vessels shall be considered a continuous load.

427.10 General. Equipment shall be identified as suitable for the chemical, thermal, and physical environment, and installed in accordance with the manufacturer's drawings and instructions.

427.12 Thermal Protection. External surfaces that operate at temperatures exceeding 60 degrees C (140 degrees F) shall be physically guarded, isolated, or thermally insulated to protect against contact by personnel in the area.

427.13 Identification. The presence of electrically heated pipelines, vessels, or both, shall be evident by the posting of appropriate caution signs or markings at intervals not exceeding 6 m (20 ft) along the pipeline or vessel and on or adjacent to equipment in the piping system that requires periodic servicing.

The 20-foot interval is a specific, tested number.

427.14 Corrosion Protection. Ferrous and nonferrous metal raceways, cable armor, cable sheath, boxes, cable trays, cabinets, elbows, couplings, nipples, 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 judged suitable for the condition, or where provided with corrosion protection approved for the condition.

427.15 Not Permitted in Hoistways. Pipeline and vessel heating equipment shall not be installed in hoistways.

427.16 Equipment Grounding. All fixed electric heating equipment for pipelines and vessels shall be grounded as required by Article 250.

Part IV — Impedance Heating

427.25 Personnel Protection. All accessible external surfaces of the pipeline or vessel being heated shall be physically guarded, isolated, or thermally insulated with a weatherproof jacket to protect against contact by personnel.

427.26 Isolation Transformer. A dual-winding transformer with a grounded shield between the primary and secondary windings shall be used to isolate the distribution system from the heating system.

427.28 Voltage Limitations. The secondary winding of the isolation transformer connected to the pipeline being heated shall not have an output voltage greater than 30 volts AC. Where the voltage exceeds 30 volts, ground-fault protection of equipment shall be provided.

The Key Rule — 427.22

427.22 Equipment Protection. Ground-fault protection of equipment shall be provided for electric heating equipment. Exception: In industrial establishments where there is alternating current equipment ground-fault protection and continued circuit operation is necessary for safe operation of equipment or processes, and where only qualified persons will service the installed systems, and continuous circuit operation is necessary for safe operation of equipment or processes.

Again, GFPE — not a Class A GFCI.

427.55 Disconnecting Means. All fixed electric pipeline or vessel heating equipment shall be provided with a means for disconnection from all ungrounded conductors. Where readily accessible to the user, the branch-circuit switch or circuit breaker shall be permitted. The disconnecting means shall be of the indicating type and be provided with a positive lockout in the off position.

427.57 Controllers. Each heating system shall be provided with an approved means for setting the maintenance temperature.

Practical Alaska Considerations

Nuisance tripping. Heat trace failures usually appear first as increasing leakage current. A GFPE device that trips intermittently is reporting a real problem, most often moisture ingress at a splice, a cold-lead termination, or a cable crushed by insulation cladding. Replacing the GFPE device with a plain breaker to "solve" the tripping is both a Code violation and a fire cause.

Cold-start inrush. Self-regulating heating cable draws several times its steady-state current at low temperature because the conductive polymer core's resistance falls as temperature falls. Manufacturers publish start-up current curves; the branch-circuit device must accommodate the start-up current without nuisance tripping while still satisfying 426.4 and 427.4 continuous-load sizing at 125 percent of steady-state load. This is a design calculation that comes from the manufacturer's data, made enforceable through 110.3(B).

Roof and gutter cable. Article 426 applies. The equipment must be identified as suitable for the environment (426.10), guarded or insulated where surfaces exceed 60 degrees C (426.12), marked with caution signs (426.13), supplied at 125 percent (426.4), and protected by GFPE (426.28), with a lockable, indicating disconnect (426.50).

Buried ramp heating. Article 426 Part II applies: an asphalt or masonry base at least 2 inches thick, 1.5 inches of cover, cables secured while the finish is applied, spacing not closer than 1 inch on centers, not more than 120 watts per square foot, and no crossing of cables.