Your questions answered: Electrical: Data and communications cabling and pathways

The June 22, 2017, “Electrical: Data and communications cabling and pathways” webcast presenters addressed questions not covered during the live event.


The June 22, 2017, “Electrical: Data and communications cabling and pathways” webcast presenters addressed questions not covered during the live event. Courtesy: TEECOMData and communications cabling distributes information from one place to another. The concept is simple enough. However, it quickly becomes more complex. NFPA 70: National Electrical Code (NEC) and other codes and standards provide guidelines—and impose limitations—regarding the distances, support, and composition of the cables that distribute information throughout buildings.

Adding to this complexity is getting the cabling from one place to another. System design also includes supporting and protecting the cables throughout the campus or facility from physical damage and/or fire or power systems via conduit, cable trays, raceways, and cable routing assemblies. When designing network distribution systems, engineers must consider where cables, and the systems that support and protect them will be used; the types and quantity of cables to be supported; and applicable codes and standards.

Other issues include distance limitations, selecting cables to support new technologies, cable insulation, and firestopping.

  • Tim Kuhlman, PE, RCDD, CDT, Associate Principal, TEECOM, Portland, Ore.
  • David Wells, RCDD, Director of Telecommunications, NV5, Las Vegas

The June 22, 2017, “Electrical: Data and communications cabling and pathways” webcast presenters addressed questions not covered during the live event.

Question: In cable tray fill, do you calculate to 50% fill or are you permitted to do more of the cross-sectional area?

Tim Kuhlman, PE, RCDD, CDT, Associate Principal, TEECOM, Portland, Ore.David Wells, RCDD, Director of Telecommunications, NV5, Las VegasTim Kuhlman: Yes, I calculate at 50% fill for ladder or ventilated type cable trays. The requirements to calculate fill depends on the circuit type. For a “communication circuit” (as defined by NEC 800.2), there are no fill requirements per Article 800. Because Article 800 does not reference the fill requirements for trays in Chapter 3, the fill requirements don’t apply because 800 stands alone unless it specifically references an article in Chapters 1 through 7 (see Figure 90.3 Code Arrangement). Therefore, for a communication circuit, I would fall back on the Standard TIA-569-D for tray fill. Paragraph states the maximum fill for a tray is to be 50% and that a 50% calculated fill will appear to be 100% full to the top of the tray. For the same cable but for a data circuit, I would look at the fill requirements under NEC Article 725. Per 725.3 and 725.133, 725.136(G), and Table 392.10 (A), cable trays are allowed to be used for Class 2 and 3 cables. There are no limitations for fill in Article 725. Therefore, the general requirements in Chapters 1 through 4 apply. Article 392.22 (A) (2) addresses the number of conductors in a tray for multiconductor signal cables. For a ladder or ventilated tray, it says 50%. So, for a communication circuit or a data circuit, 50% fill is the number.

Q: Please discuss design considerations to prevent electromagnetic interference (EMI). Any national/international color standards to differentiate between fire alarm, security, lighting, and HVAC controls, data, etc. cabling?

David Wells: Refer to the TIA-569 pathways and spaces standard for EMI consideration and refer to the TIA-606 standard for coloring standards for different cabling types.

Q: Due to cost and the efficient use of space, what is the pathway type used for main pathway routings?

Kuhlman: I would recommend cable tray as the most efficient use of space, the least amount of cost, and best protection for the cable. If you still have access to the presentation slides, refer to slide 23 with the cable support methods comparison chart.

Q: Is it permissible to attach to sprinkler pipe or sprinkler hangers?

Wells: It is NOT permissible. Please refer to NFPA 13 section 9.1

Q: What type of listing is required for cables between buildings and exposed to outdoor weather?

Kuhlman: There is no outdoor or wet-rated NEC listing for a data, communications, or fiber cable by the NEC, and the NEC does not require this listing. However, the NEC does state for data circuits, the cable placed in wet or damp environments is to be rated for the environment. See Article 725.3 (L). Article 725 does not have a specific NEC designation for a wet-rated cable, such as what NEC Chapter 3 has for power conductors. For cables extending beyond a building, Article 725.141 refers you to Chapter 8. The only place I see in Article 800 that addresses a wet rating is in Article 800.47 where it states “the requirements of Article 310.10(C) shall not apply to communications cabling and wiring. Article 310.10(C) provides wet location cable designations. To meet the code requirement, the cable needs to be intended for outdoor or wet environments by the manufacturer.

Q: What is best? CAT-6?

Wells: Selection of the type of category cabling depends on the job requirements. CAT-3, CAT-5E, CAT-6, CAT-6A, and CAT-8 are all recognized by the TIA standards. Most installations today are using either CAT-6 or CAT-6a.

Q: Can you discuss Class 1, 2, and 3 cables in more detail?

Kuhlman: This is a very broad question. NEC Article 725 is where this is defined by the code. I can’t speak to Class 1 circuits, but for Class 2 and 3 circuits, this is defined by the load side of the power supply and the designation of the component for one of the five criteria listed in Article 725.121 (A).

Q: Please discuss structured cable issues, and local area network (LAN) room issues.

Wells: Please refer to TIA-569 for pathways and spaces and TIA-568 for cabling issues.

Q: NEC Article 645 applies to a computer room? Is this true?

Kuhlman: This is true. The NEC does not provide a good definition for Information Technology Equipment. The definition in 645.2 states: “Information Technology Equipment Room. A room within the information technology area that contains the information technology equipment. [75:3.3.9]” The key here is to look at the cited reference for NFPA 75. NFPA 75 also is the very first piece of text referenced in an information note at the start of this section, right below the title. So, to get a good definition, I would look at NFPA 75 The Protection of Information Equipment. In the heart of NFPA 75, you still get the same circular logic definition that the NEC provided. The key is to look at NFPA 75 Origins and Development on the 4th page and in the third paragraph. It states “In editions of this standard prior to 2003, the terms “electronic computer/data processing equipment” and “electronic computer system” were used where the current terms “information technology equipment” and “information technology equipment system,” respectively, are used. Similarly, the terms “computer room” and “computer area” were replaced by “information technology equipment room” and “information technology equipment area,” respectively.

Q: Please discuss requirements to transition from OSP to inside building cable.

Wells: Please refer to NEC 820.48. Measured from point of entrance, cabling cannot extend past 50 feet into the building without being installed in conduit.

Q: What is the current status of CI cable and the UL problems it had with not meeting the 2-hour rating?

Kuhlman: I have talked to five manufactures of fiber and CAT-6 cabling in the past 6 months and none of them are making cable to meet the 2-hour rating circuit integrity cable requirements. There are some cables out there that will meet the flame requirement, but they are manufactured for us on ships and don’t have an NEC-recognized listing to all them to install in buildings.

Q: Please discuss CAT-6 wiring conduit fill capacity.

Wells: Conduit fill is determined by the outer diameter (O.D.) of the cable. Each manufacture has slightly different O.D. for its CAT-6 cable. After the O.D. is determined, you should be able to use a conduit fill calculator to determine the fill capacity.

Q: When my cable TV company installs a cable in my house, is the installer expected to know the standards and codes?

Kuhlman: Yes. Each state, county, or city has accepted some form the electrical code. However, it varies from jurisdiction to jurisdiction whether they explicitly require it or enforce it. The NEC does not apply to a “utility” (NEC 90.2 (B)(5)(b) but that only applies for facilities that are under complete control of the utility. Your house is under your control and whether you hire an electrician or a CATV company to install cable in or on your building, it needs to meet the requirements of the building code for your jurisdiction.

Q: Discuss cable types (CAT-5E/CAT-6a, G-PON Fiber).

Wells: CAT-3, CAT-5E, CAT-6, CAT-6A, and CAT-8 are all recognized by the TIA standards. Most installations today are using either CAT-6 or CAT-6a. When GPON is deployed, it is a passive optical network using fiber optical passive splitters enabling a single fiber to serve multiple outlets.

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