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National Electrical Code: Grounding and Bonding Case History

by Mark Lamendola

A Master Electrician relates this true story:

The electrical services firm I work for sent me to a plant that had all kinds of power quality problems. The "geniuses" there decided to "isolate" the equipment so it wouldn't "pick up noise from ground." So the whole place floated. It took me about three hours to understand how they had configured their system (no drawings, naturally). They had an ungrounded 480Y277 system. They had even removed the bonding jumpers inside the transformer housings at every drop on the 480V system, which also blew my mind. So they didn't understand grounding OR bonding.

We did manage to get them to approve bonding the equipment, but they told us we could NOT tie the service to any ground rods. I said we MUST tie the service entrance ground to earth via an electrode system of some sort and they said absolutely not.

At that point, I called the frickin' utility and had them send a couple guys out to explain why ground was needed. The breaker operation argument didn't work, because the customer had been told you don't need ground for a breaker to operate. The lightning protection argument didn't work, but--even though they had aerials on their roof--I did not understand why (they had just one insulated downconductor--"isolated" from building steel--running way out to an electrode at the edge of their property, and it wasn't tied to the service ground). The "we will shut your power off if you donít do it" argument did work--imagine that.

This was originally a thermography job, and it quickly morphed into a battle with a customer--in this case, it was a public safety issue and we couldn't just walk away from it. Half the crew walked off the job when they found out there was NO grounding, further complicating this project. They said they'd come back to fix that if the utility would shut the power off (which they did!). Our guys were afraid of being electrocuted from touching a raceway feeding the 277V loads.

That was the most screwed up place I had ever seen. I told my boss they must have a collective IQ of about 40, and he told me to quit flattering them.

 

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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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