National Electrical Code ExplanationsBased on the 2014 NEC
National Electrical Code Tips: Article 820, Community Antenna Television and Radio Distribution Systems
- Because Article 820 covers cable distribution of radio frequency signals typically employed in community antenna (CATV) systems [820.1], it is increasingly less applicable. Those systems are pretty much from a bygone era.
- Many of the requirements in Part I are found elsewhere in the Code or just derive from the intent of the Code and common sense. An example are the requirements for mechanical execution of work [820.24]. Another example is what you do with abandoned cables [820.25].
- When outside cables enter buildings, they must meet the requirements of Part II [820.44 - 820.49].
- When outside cables enter buildings are in metallic conduit (RMC or IMC), the conduit must be connected by a bonding conductor or grounding electrode conductor to a grounding electrode [820.49]. This rule exists for lightning protection. Now, understand that where you have utilities entering near the same point and each has its own ground rod you must bond these rods together to prevent differences of potential. So for Article 820, you can simply bond that conduit to an existing rod or to an existing bonding jumper that runs between the rods. You don't have to drive a separate ground rod, but if you do then it must be bonded anyhow. If the cable entrance is on one side of the building all by itself, there's no danger of flashover to the other ground rods that simply are not there. So you drive one ground rod for that conduit. You don't have to run a bonding jumper all the way around the other side of the building to correct for a flashover problem that does not exist.
- Part III is titled "Protection" and this is really about the same thing that 820.49 is about: eliminating dangerous differences of potential.
- Part IV provides bonding and grounding requirements. These requirements are similar in many ways to those for lightning protection systems (e.g., take the shortest route possible but run in as straight a line as possible), for the same underlying reasons.
- The NEC lets you rely upon the cable sheild for equipment bonding [820.103]. However, good engineering practice means running dedicated bonding jumpers. If, for example, the coaxial cable is disconnected for repairs, maintenance, or replacement what do you think happens to your bonding connection? It goes away.
- Part V provides the requirements for installation methods within buildings. Most of this has to do which types of cables are allowed where. It's a lot to wade through, but the good news for the bulk of it is you just need to find the applicable application in 820.113(A) through (K).
- Two useful tables are in Part V: Table 820.154(a) Applications of Listed Cables in Buildings and Table 820.154(b) Coaxial Cable Uses and Permitted Substiutions.
- Part VI provides the listing requirements. It is a good idea to be thoroughly familiar with these.
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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.
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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.