National Electrical Code ExplanationsBased on the 2014 NEC
National Electrical Code Tips: Article 770, Optical Fiber Cables and Raceways, Part 3
Understanding the listing requirements of fire alarm circuit cables can help you make sense of the cable alphabet soup. Here are some highlights from Part IV of Article 770.
- The requirements for installing these cables within buildings are in Part V. It dominates Article 770 relative to the other requirments, taking up slightly more than four pages. A full page is devoted to table that outlines the applications of listed optical fiber cables within buildings.
- You can install these cables in any raceway that complies with Chapter 3 [770.110(A)]. Alternatively, you can use listed: plenum communication raceways, riser communications raceways, and/or general-purpose raceways [770.110(A)].
- What about the raceway fill for these cables? That depends upon whether the cables include currenty-carrying conductors or not. If they do, then the raceway fill requirements of Chapters 3 and 9 apply [770.110(B)(2)]. Otherwise, they don't [770.110(B)(1)]. In the latter case, that doesn't mean you jam those raceways as full as possible. There are other considerations (which the NEC does not address) that come under the purvey of good design practices, realistic expectations for not damaging the cables during installation, maintenance issues, and workmanship.
- With the 2014 NEC, a new subsection was added to 770.110. That is subsection C. It provides the requirements for cable routing assemblies. It may be worth noting that all of the previous 770.110 was added with the 2011 NEC. That particular revision was loaded with extensive changes.
- Section 770.113 was all new with the 2011 NEC. It provides the installation requirements for optical fiber cables. At first glance, it seems mind-boggling because it's full of cable type abbreviations and stretches from subsection (A) through subsection (J). But don't worry, that structure allows you to quickly locate the applicable requirements.
- To quickly navigate through 770.113, first look for your application. For example, you are installing in plenums. That would bring you to 770.113(C). Installing in a fireproof shaft? You work per 770.113(F).
- Lots of new stuff came into Article 770 in 2011. Section 770.114 is yet another example. For the 2014 revision, it remains unchanged. Basically, this extends the Article 250, Part V requirements to the non-currenty-carrying conductive members of optical fiber cables. But don't make the mistake of parsing out Code requirements just to meet the minimums. Even where the NEC does not explicitly require doing so, you want to bond all metallic components (other than current-carrying) of your system.
- As noted in Part 2 of this series, Article 770 leaves plenty of room for expansion. We leap from Section 114 to Section 133 (in the 2014 NEC). Here, you'll find the requirements for installing optical fibers and electrical conductors. Recall that 770.113 provided the requirements for installnig optical fibers. So 113 if just the fiber cables, but 133 if anything else is included in that run (namely, electrical conductors, communications cables, and/or other circuits).
- Earlier, we mentioned that big table of applications. It's Table 770.154(a). This table shows three groupings of cable types across the top and four types of installations going down the left side. So you can go to your type of installation (e.g., "In risers") and see what cable type(s) are permitted. The type of installation is broken down into variations, so make sure you are looking at the correct variation. For example, you can use Type OFC cable in risers in metal raceways; but not in vertical runs (there are other exclusions, too).
- The final Table in Part V is Table 770.154(b). If you are thinking about cable substitutions, you need to reference this Table.
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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.