system that requires periodic servicing.
III. Resistance Heating Elements
427.14 Secured. Heating element assemblies shall be secured to the surface being heated by means other than the thermal insulation.
427.15 Not in Direct Contact. Where the heating element is not in direct contact with the pipeline or vessel being heated, means shall be provided to prevent overtemperature of the heating element unless the design of the heater assembly is such that its temperature limitations will not be exceeded.
427.16 Expansion and Contraction. Heating elements and assemblies shall not be installed where they bridge expansion joints unless provisions are made for expansion and contraction.
427.17 Flexural Capability. Where installed on flexible pipelines, the heating elements and assemblies shall have a flexural capability that is compatible with the pipeline.
427.18 Power Supply Leads.
(A) Nonheating Leads. Power supply nonheating leads (cold leads) for resistance elements shall be suitable 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 427.20 are retained.
(B) Power Supply Leads Protection. Nonheating power supply leads shall be protected where they emerge from electrically heated pipeline or vessel heating units by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, or other raceways identified as suitable for the application.
(C) Interconnecting Leads. Interconnecting nonheating leads connecting portions of the heating system shall be permitted to be covered by thermal insulation in the same manner as the heaters.
427.19 Electrical Connections.
(A) Nonheating Interconnections. Nonheating interconnections, where required under thermal insulation, shall be made with insulated connectors identified as suitable for this use.
(B) Circuit Connections. Splices and terminations outsjde the thermal insulation shall be installed in a box or fitting in accordance with 110.14 and 300.15.
427.20 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.
427.22 Equipment Protection. Ground-fault protection of equipment shall be provided for electric heat tracing and heating panels. This requirement shall not apply in industrial establishments where there is alarm indication of ground faults and the following conditions apply:
(1) Conditions of maintenance and supervision ensure
that only qualified persons service the installed systems.
(2) Continued circuit operation is necessary for safe operation of equipment or processes.
427.23 Grounded Conductive Covering. Electric heating equipment shall be listed and have a grounded conductive
covering in accordance with 427.23(A) or (B). The conduc
tive covering shall provide an effective ground path for equipment protection.
(A) Heating Wires or Cables. Heating wires or cables shall have a grounded conductive covering that surrounds the heating element and bus wires, if any, and their electrical insulation.
(B) Heating Panels. Heating panels shall have a grounded conductive covering over the heating element and its electrical insulation on the side opposite the side attached to the surface to be heated.