National Electrical Code ExplanationsBased on the 2014 NEC
National Electrical Code Tips: Article 840, Premises-Powered Broadband Systems
- Article 840 is the last Article in the NEC (as of the 2017 Code). It is not the last place to find valuable information. Past this point in the NEC you'll find useful tables an annexes.
- The Scope of Article 840 was expanded with the 2015 NEC. For example, it now covers twisted pair wiring [840.1].
- At the end of Part I are four subsections that reiterate principles/requirements that are found elsewhere in the NEC repeatedly: 1. Don't block access behind panels [840.21]; 2. Mechanical execution of work needs to be neat and workmanlike [840.24] except in this case you're referred to three other places for additional details; Abandoned cables have to be labeled as such [840.25] except in this case you go elsewhere to actually read that; and 4. You can't substantially increase the spread of fire [840.25] and again you are directed elsewhere.
- Part II is titled "Cables Outside and Entering Buildings". Most of the text provides requirements for overhead optical cables [840.44] (all about clearances) and underground wires and cable [840.47].
- 840.45 and 840.46 simply say that 840.44 applies to overhead communications wires and cables and to overhead coaxial cables.
- Part III provides "protection" requirements. It does so in a verbose and convoluted way. Basically, you must either ground (bond to the equipment grounding jumper) these incoming cables or install an interrupting device on them.
- Part IV contains the grounding requirements. Much of this is done by referring to other requirements. That makes sense for consistency of application, but following all these text jumps can be confusing. If you're going to do a project covered by Article 840, look up all of the "grounding" (it's typically bonding, instead) requirements and write them down in one place. Alternatively, you can just note that if it's metallic it needs to be bonded to the equipment bonding jumper and that includes any driven ground rods. Do not drive a ground rod for this system and let it float relative to other ground rods; that creates a dangerous difference of potential.
- Grounding and bonding requirements for mobile homes get special mention in their own section [840.106].
- Part V provides requirements for installation methods within buildings. The actual text will be in 770.110, 800.110, or 820.110 depending upon the type of cable (optical fiber, multipair, or coaxial, respectively).
- The communications cables can carry power wiring, too. But if the power exceeds 60W, then additional requirements apply [840.160].
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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.