12.5 Snow-Melting & De-Icing Equipment (Article 426) and Pipeline & Vessel Heating (Article 427)

12.5 Snow-Melting & De-Icing Equipment (Article 426) and Pipeline & Vessel Heating (Article 427)

The PSI outline lists space-heating, snow-melting, and pipe-heating circuits as a single sub-topic, but the Code splits that work across three articles. Knowing which article to open is half the question:

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1. Article 426 — Fixed Outdoor Electric Deicing and Snow-Melting Equipment

Article 426 applies to embedded or exposed heating equipment installed outdoors in driveways, walkways, steps, ramps, roofs, gutters, downspouts, and similar areas. Three concepts carry the article.

Installation types

• Embedded (Part II). Heating cable, panels, or units are cast into concrete, masonry, or asphalt. The Code addresses spacing between adjacent runs so heating elements do not overheat each other, prohibits panels or units from bridging expansion joints unless protection against expansion and contraction is provided, requires that cable ends be terminated and insulated before the pour, and requires that the installation be inspected and tested before the covering material is applied.
• Exposed (Part III). Cable installed on roofs, in gutters, and on downspouts must be secured with means that will not damage the sheath and must be arranged so that ice and snow loading cannot pull the cable loose.
• Skin-effect heating (Part IV). A ferromagnetic tube with an insulated conductor inside carries current that returns on the inner surface of the tube; the tube itself is not a raceway in the ordinary sense but is treated as an enclosure for the internal conductor.

Ground-fault protection of equipment (426.28)

NEC 426.28 requires ground-fault protection of equipment for fixed outdoor electric deicing and snow-melting equipment. This is not a Class A GFCI:

The protection may be built into the branch-circuit breaker (a GFPE-rated breaker) or supplied as an integral device that is part of the listed deicing or snow-melting equipment.

Identification, use, and control

• 426.13 requires that the presence of deicing or snow-melting equipment be made evident by posted caution signs or permanent markings on fixed pedestals and equipment, so someone drilling an anchor into a heated slab has been warned.
• 426.11 requires the equipment to be identified as suitable for the chemical, thermal, and physical environment in which it is installed.
• 426.4 treats the fixed outdoor electric deicing and snow-melting load as a continuous load, which means the branch-circuit conductors and overcurrent device are sized at 125 percent of the load.
• 426.14 permits certain installations only with special permission from the authority having jurisdiction.
• Part V covers controllers and disconnecting means: the equipment must have a means of disconnect, and where the heating equipment is supplied by a remote panel, the disconnecting means must be capable of being locked in the open position.

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2. Article 427 — Fixed Electric Heating Equipment for Pipelines and Vessels

Article 427 covers electrically energized heating systems and their controls applied to pipelines and vessels — freeze protection on a fire-suppression standpipe, viscosity maintenance on a fuel-oil line, and process temperature maintenance in a refinery are all Article 427 work.

The five heating technologies

1. Resistance heating elements — self-regulating or constant-wattage heat trace cable spiraled or straight-traced along the pipe under insulation.
2. Impedance heating — current is passed through the pipe itself, with the pipe acting as the resistive element; the voltage is limited and the pipe must be effectively grounded.
3. Induction heating — an isolated coil around the pipe induces current in the pipe wall.
4. Skin-effect heating — an insulated conductor inside a ferromagnetic tube welded to the pipe.
5. Heating panels and jackets applied to vessels.

The three rules the exam asks for

• 427.13 Identification. The presence of electrically heated pipelines or vessels must be evident by caution signs or markings at intervals not exceeding 20 feet (6.0 m) along the pipeline or vessel and on or adjacent to the equipment. A welder cutting into an unmarked traced line is exactly the hazard this rule addresses.
• 427.22 Equipment protection. Ground-fault protection of equipment is required for electric heat tracing and heating panels. The single exception is for industrial establishments where there is alarm indication of ground faults and where conditions of maintenance and supervision ensure that only qualified persons service the installed systems — a plant may then trade automatic disconnection for monitored operation, because losing freeze protection can itself be a hazard.
• Disconnecting means. Means must be provided to disconnect all ungrounded conductors of each heating application, and where the heating equipment is remote from its supply, the disconnect must be lockable in the open position.

Installation practice that shows up as a scenario

• Heat trace is installed under the thermal insulation, and the insulation must be kept dry — wet insulation destroys both the heating performance and the cable.
• The thermostat or controller sensing bulb must be located on the pipe, not in the ambient air, unless the system is designed for ambient sensing.
• Heating cable may not be installed through walls where it will be concealed unless the specific installation is permitted by the article, and cable ends must be terminated with listed kits.
• Heating loads are continuous loads — size branch-circuit conductors and the overcurrent device at 125 percent of the total heating load.