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National Electrical Code Articles and Information

National Electrical Code Top Ten Tips:
Article 427 -- Fixed Electric Heating Equipment for Pipelines and Vessels

by Mark Lamendola

Based on the 2020 NEC

Please note, we do quote from copyrighted material. While the NFPA does allow such quotes, it does so only for the purposes of education regarding the National Electrical Code. This article is not a substitute for the NEC.

These are the 10 NEC Article 427 items we deem most important, based on the pervasiveness of confusion and the potential costs of same.

  1. Know the difference between Impedance, Inductance, Integrated, Resistance, Skin-effect and heating systems [427.2]. Each has its own installation requirements.
  2. Fixed heating systems for pipelines and vessels are always continuous loads [427.4]. Normally, when you are using one you are using them all. It's not like the situation where you have mixed use loads that aren't normally run at max capacity at the same time--for example, 24 receptacles in an office area.
  3. Not all equipment that might be used for this purpose can be used for this purpose. Ensure that it's identified for the chemical, thermal, and physical environment [427.10]. If in doubt, contact the manufacturer.
  4. Equipment identified for this purpose must be installed in a manner that doesn't violate its suitability for the purpose. Consult and follow the manufacturer's instructions [427.10].
  5. The requirements for resistance heating elements are not obvious, so you must consult Part III to know what they are. For example, do you know what to do when the heating element is not in direct contact with the pipeline or vessel being heated?
  6. The requirements for impedance heating elements are not obvious, so you must consult Part IV to know what they are. For example, do you know what an isolation transformer is used for in this application?
  7. The requirements for inductive heating elements are not obvious, so you must consult Part V to know what they are. For example, do you know the requirement that applies when the induction coils operate or may operate at greater than 30V?
  8. The requirements for skin-effect heating elements are not obvious, so you must consult Part VI to know what they are. For example, do you know what requirement you must meet if you want to bury a pullbox under the insulation?
  9. The rules for the disconnecting means changed with the adoption of the 2002 NEC. A controller can serve as the disconnect, if it conforms to 427.55 and 427.56(D).
  10. Article 427 does not provide separate requirements for overcurrent protection. You protect the heating equipment against overcurrent when you supply it by a branch circuit as specified in 210.20 and 210.24 (prior to the 2020 revision, it was 210.18 and 210.23).


How the NEC is arranged

  1. The first four Chapters of the NEC apply to all installations.
  2. Article 90 precedes Chapter One, and establishes the authority of the NEC.
  3. Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
  4. Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
  5. Chapter 8 provides the requirements for communications systems.
  6. Chapter 9 provides tables.
  7. The appendices provide mostly reference information.
  8. Appendix D contains examples that every NEC user should study.

Try your NEC moxy:

  • Do you know the difference between bonding and grounding? Hint: Look in the NEC, Article 100.
  • Does the NEC refer to grounding incorrectly in any of its articles? Yes! So be careful to apply the Article 100 definitions. Don't ground where you should bond.
  • When doing motor load calculations, which Article covers hermetic motors? Answer: While Article 440 covers the application of hermetic motors, it does so only by amending Article 430 because hermetic motors are a special case of motors. For motor load calculations, refer to Article 430.
  • Does the NEC provide a voltage drop requirement? Yes! It does so in a special case, which is Article 648 Sensitive Electronic Equipment. But for general applications, it does not provide a requirement; it merely provides a recommendation in a couple of FPNs.
  • Take our Code Quizzes.

Remember other applicable codes, rules, standards, and references:

  • OSHA's electrical worker safety rules.
  • IEEE standards.
  • NETA standards.
  • NFPA standards.
  • International Codes (if applicable to the installation).
  • State Codes (if the state has them).
  • Local ordinances and permit requirements.
  • Local fire codes.
  • Manufacturer requirements or guidelines.
  • Customer security requirements.
  • Industry standards.
  • Your company's own internal standards, practices, and procedures.
  • Engineering drawing notes.


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