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 a table that outlines the applications of listed optical fiber cables within buildings [770.154(A).
- 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). Fortunately, the CMP saw fit not to juggle these around for the 2014, 2017, and 2020 revisions.
- Lots of new stuff came into Article 770 in 2011. Section 770.114 is yet another example. For the 2014, 2017, and 2020 revisions, 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 leapt from Section 114 to Section 133 in the 2014 NEC and nothing was inserted between them in 2017 or 2020. In Section 133, you'll find the requirements for installing optical fibers and electrical conductors. Recall that 770.113 provided the requirements for installing optical fibers. So Section 113 is for just the fiber cables, but Section 133 is for anything else 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.
A similar (not identical) table appears in Article 760, and is also 154(b).