National Electrical Code ExplanationsBased on the 2014 NEC
National Electrical Code Tips: Article 800, Communications Circuits, Part 4
- Article 800, Part IV is titled, "Grounding Methods." And this is where the confusion starts. To correctly understand and implement Par IV, go to Article 100 and read the definitions of grounding and bonding. For communications circuits, you must do both. But you cannot substitute one for the other.
- The title of 800.100(A) is Bonding Conductor or Grounding Electrode Conductor. What's the difference? The bonding conductor is what connects all the metallic parts and puts them at the same potential; don't be surprised to find several seperate conductors forming the bonding system. The grounding electrode conductor connects the bonding conductor (usually through a single connection to one actual conductor in the bonding system) to (usually a single) grounding electrode.
- Note that this grounding electrode must be connected to the grounding electrode(s) of any other system [250.94].
- Use a bonding conductor and/or grounding conductor that's compatible with the material your grounding electrode(s) is made of. In any case, it must be a corrosion-resistant conductive material [800.100(A)(2)]. The bonding and grounding conductors are typically copper. And it doesn't matter if they are solid or stranded; choose this based on what's best for the particular application.
- How big must your bonding conductor be? What about your grounding conductor? These have to be at least 14AWG. That doesn't mean you can just use 14AWG, however. They must also have a current carrying capacity that's not less than that of the grounded metallic sheath member(s) and protected conductor(s) of the communications cable. But the limit there is 6AWG; these don't have to be larger than 6AWG [800.100(A)(3)]. That said, nothing stops you from using 4AWG either. Doing so results in a system that will be immune to damage from string trimmers.
- How long must your bonding conductor be? What about your grounding conductor? The NEC says, "As short as practicable." [800.100.(A).4]. This doesn't mean as short as possible. Apply good workmanship so that you route these conductors out of harm's way, include no sharp bends, and ensure they are properly supported. This means the length of your installation will be considerably more than "shortest possible."
- There is an Exception to this shortness rule. It's kind of detailed and applies to one- and two-family dwellings.
- One key to getting these conductors as "short as practicable" is you run them in as straight a line as is practicable [800.100.(A).5]. Yet here again, the goal is constrained by good workmanship. Sure, you could run the grounding conductor in a perfectly straight line across the diagonal of the triangle formed between your bonding conductor, the ground, and the grounding electrode. But a correct installation means you run down the vertical line of that triangle and then horizontally under the soil and then up again to connect to the grounding electrode clamp (this last assumes the grounding electrode sticks up, which is typical).
- All that shortness and straightness is further constrained by the need to ensure protection against physical damage [800.100.(A).6]
- You also don't want a difference of potential between one of these conductors and the metal raceway you run them in (if you do run them in such). Ensure you bond each end of the raceway to the contained conductor or to the same terminal or electrode to which the conductor is connected [800.100.(A).6].
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Learn more about:
How the NEC is arranged
- The first four Chapters of the NEC apply to all installations.
- Article 90 precedes Chapter One, and establishes the authority of the NEC.
- Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
- Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
- Chapter 8 provides the requirements for communications systems.
- Chapter 9 provides tables.
- The appendices provide mostly reference information.
- 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.