By Stanley Kaufman, PhD, CableSafe Inc.
The National Electrical Code (NEC) is published by the National Fire Protection Association (NFPA; www.nfpa.org) with revisions on a three-year schedule. The 2017 NEC, which replaces the 2014 NEC, was released by the NFPA in August 2016.
This article, sponsored by SPI: The Plastics Industry Association (formerly known as The Society of the Plastics Industry), is intended to provide the reader with a guide to the key changes in the 2017 National Electrical Code that are of interest to manufacturers, installers, distributors and users of data/comm cables.
NFPA 70, NFPA, National Fire Protection Association, National Electrical Code and NEC are registered trademarks of the National Fire Protection Association.
Data/comm cables
Although widely used in the industry, the term data/comm cable does not appear in the NEC. The term data/comm cable, as used in this article, encompasses six families of cable types in the NEC, described in the table.
Note that cable types CMX, CL2X, CL3X and CATVX are not included in the table of data/comm cables because of the very limited applications of these cables.
Temperature limits of data/comm cables
The concept of temperature limits on electrical conductors is a fundamental safety requirement in the National Electrical Code. Section 310.15(A)(3) in Article 310, Conductors for General Wiring, in the 2014 and 2017 editions of the NEC requires that electrical conductors be installed and operated so they do not exceed their temperature limits. This long-standing requirement is in Section 310-9 in the 1978 NEC, which happens to be the oldest code book in this author’s library.
This fundamental requirement in the 2014 NEC applies to cables used for Class 2, Class 3 and power-limited fire alarm circuits; including, of course Class 2, Class 3 and power-limited fire alarm cables. This requirement also includes communications cables that are used as substitutes for Class 2, Class 3 and power-limited fire alarm cables.
Section 90.3, Code Arrangement, states that “Chapter 8 is not subject to the requirements of Chapter 1 through 7 except where the requirements are specifically referenced in Chapter 8.” Since there are no references to Section 310.15(A)(3) in Chapter 8 in the 2014 NEC, there are no requirements in the 2014 NEC that communications cables and CATV coaxial cables should be operated so as not to exceed their temperature ratings.
In the 2014 NEC, the applicability of Section 310.15(A)(3) to Class 2, Class 3 and power-limited fire alarm cables is tenuous because there are no temperature limitations in the listing requirements for Class 2, Class 3 and power-limited fire alarm cables in Sections 725.179 and 760.179; the temperature limits are in the listing documents, UL 13, Standard for Power-Limited Circuit Cables, and UL 1424, Standard for Cables for Power-Limited Fire-Alarm Circuits. Since the listing documents require that the temperature limit be marked on a cable only if it exceed 60 degrees Celsius (140 degrees Fahrenheit), an electrical inspector would have difficulty determining the temperature limit of an unmarked cable.
The applicability of Section 310.15(A)(3) to optical fiber cables is also tenuous, since this section applies to current-carrying conductors and there are no current-carrying conductors in optical fiber cables. Recall that Section 770.3(C) requires that cables containing optical fibers and electrical conductors (composite cables) be classified according to the type of electrical conductor.
The 2017 NEC addressed these ambiguities in the applicability of temperature limitation requirements by requiring that all data/comm cables have a temperature rating of at least 60 degrees C (140 degrees F) and have the temperature rating marked on the cable if it exceeds 60 degrees C. New Section 800.3(H) requires that cables used in communications circuit installations comply with Section 310.15(A)(3). The only cables permitted to be used for communications circuits are communications cables, i.e. Types CMP, CMR, CMG, CM and CMX.
Powering over data/comm cables
While data/comm cables are widely used for simultaneously powering and communicating/signaling with equipment, the 2014 NEC does not explicitly address the issue that cables that were designed for transmission of data are now carrying sufficient power that the cables may overheat, i.e. exceed their temperature ratings. The 2017 NEC addresses this issue; it has a new section, 725.144 Transmission of Power and Data, in Article 725, Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits.
Anyone familiar with the NEC knows that the code deals with conductor heating issues through the use of ampacity tables. Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. While power conductors have “conductor” temperature ratings, in the case of data/comm cables, the “cables” have the temperature ratings. The temperature ratings of the data/comm cables apply to the conductors in the data/comm cables.
While the National Electrical Code has many ampacity tables, virtually all deal with the large conductors used in power wiring. The smallest conductor in the ampacity tables in Article 310 is 18 AWG. An ampacity table for 4-pair, 22, 23, 24 and 26 AWG cables was introduced in the 2017 NEC based on an extensive fact-finding investigation conducted by Underwriters Laboratories (UL). As indicated in the title, Fact Finding Report on Power over Local Area Network Type Cables (4-Pair Data/Communications Cables), the study was carried out on LAN cables. The ampacity table includes cables rated for 60, 75 and 90 degrees Celsius, and accounts for cable bundling, up to a bundle size of 192 cables. For bundle sizes over 192 cables and conductor sizes smaller than 26 AWG, ampacities are permitted to be determined by qualified personnel under engineering supervision.
The listing requirements for Class 2 and Class 3 cables are in Section 725.179. This section provides the listing requirements for Types CL3P, CL2P, CL3R, CL2R, CL3 and CL2 cables. The 2014 NEC includes an additional classification, circuit integrity cables. Circuit integrity cables are marked CL3P-CI, CL2P-CI, CL3R-CI, CL2R-CI, CL3-CI and CL2-CI. The 2017 NEC introduces another additional classification, limited power (LP) cables, which are listed as suitable for carrying power and data circuits up to a specified current limit for each conductor without exceeding the temperature rating of the cable.
Limited power cables are marked with the suffix “-LP” and their ampere limit, for example, Type CL2P-LP (0.6A), 22 AWG.
Section 725.144 permits “-LP” cables to be installed in bundles, raceways, cable trays, and cable routing assemblies without any limit on the amount of cables. Since the “-LP” listing is an add-on to the basic cable listing, “-LP” cables are permitted to be used in any application the base cable is permitted to be used. For example, a 75-degree C rated Type CL2P-LP (0.6A), 22 AWG cable is permitted to be used anywhere a 75-degree C rated Type CL2P, 22 AWG cable is permitted to be used. While a 75-degree C rated Type CL2P-LP (0.6A), 22 AWG cable is permitted to carry up to 0.6 ampere per conductor when the cable is installed in a cable tray with hundreds of cables, the simplified ampacity table (which only includes 75-degree C rated cables) shows that a 75-degree C rated Type CL2P, 22 AWG cable is permitted to carry up to 1.2 amperes in a 19-cable bundle.
The NECStyle Manual notes that the term “ampacity” refers to the current-carrying capacity of conductors only. It does not include, for example, the current limit of connectors used with LAN cables. New Section 725.144 has a requirement that the current in a power circuit not exceed the current limitation of the connectors. The 8P8C (8-position 8-contact) connector, which is often referred to as the RJ45 connector, is typically rated for 1.3 amperes per contact. Consequently, the maximum current permitted to be carried by each conductor in a LAN cable will often be determined by the current limits of the connector rather than the ampacity of the conductor.
New Section 725.144 provides three compliance options for installing a typical 4-pair LAN cable with 22, 23, 24 or 26 AWG conductors.
- Option one: Comply with the current and bundle size limits of the ampacity table (Table 725.144) for the gauge (AWG size) and temperature rating of the cable. The largest bundle size in Table 725.144 is 192 cables.
- Option two: If the bundles or groupings of cables are large, more than 192 cables, use “-LP” cables and comply with the current limits of the “-LP” cables. Note that this current limit of a “-LP” cable will often be less than the ampacity permitted by the ampacity table (Table 725.144) for small bundle sizes of the same cable.
- Option three: If the bundles or groupings of cables are large, over 192 cables, or conductor sizes are smaller than 26 AWG, a qualified person under engineering supervision is permitted to determine the ampacity.
The scope of Article 840, Premises-Powered Broadband Communications Systems, has been broadened. In the 2014 NEC, the scope only included services provided through an optical fiber cable. In the 2017 NEC, that limitation has been removed to permit any input, thereby recognizing systems based on ubiquitous multipair communications cables and CATV type coaxial cables. Article 840 has a new Part VI, Premises Powering of Communications Equipment over Communications Cables. New Section 840.160, Powering Circuits deals with the issues of powering communications equipment over communications cables. Section 840.160 requires compliance with Section 725.144 when the power supplied to a communications circuit over a communications cable is over 60 watts, except that Section 840.160 requires communications cables to be used rather than Class 2 or Class 3 cables permitted in Section 725.144.
Requiring use of a communications cable rather than a Class 2 or Class 3 cable is not a significant restriction because communications cables are widely used for communications as well as Class 2 and Class 3 applications. Typically, LAN cables are listed as communications cables because communications cables are permitted to substitute for Class 2, Class 3 and non-power-limited fire alarm cables. Listed communications cables, because of the permitted substitutions, are effectively universal cables for all data/comm applications.
Painting of cables
In the construction of office buildings, cables are often installed before construction is completed. Consequently, communications cables may be inadvertently spray-painted or coated with foreign substances. Painting the cables can change the cable performance properties in unknown ways. This is especially true of plenum cables, which are designed to have excellent fire resistance properties. Painting of plenum cables will likely compromise their excellent fire-safety properties.
In order to alert users to this issue, Informational Notes have been added to Article 770, Optical Fiber Cables, Article 800, Communications Circuits, and Article 820, Community Antenna Television and Radio Distribution Systems. The notes warn that paint, plaster, cleaners, abrasives, corrosive residues, or other contaminants may result in an undetermined alteration of the cable properties.
Plenum-grade cable routing assemblies
The 2017 NEC has new listing requirements for plenum-grade cable routing assemblies. The new requirements correlate with those that are specified in the 2015 edition of NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems. In the 2014 NEC, plenum-grade cable routing assemblies were listed to a less-rigorous test and they were not permitted to be installed in plenums. In the 2017 NEC, plenum-grade cable routing assemblies are permitted to be installed in plenums. Only listed plenum cables, Types CL2P, CL3P, FPLP, CMP, CATVP and BLP are permitted to be installed in plenum cable routing assemblies that are installed in plenums.
Acknowledgements: I am a consultant to SPI: The Plastics Industry Trade Association; I thank SPI for supporting the writing of this paper. Special thanks to Dan Kennefick of Daikin America; Gerald Dorna of Belden Inc. and a member of CMP-16; and Fred Dawson of Chemours, a member of CMP-16, for insightful advice and comments.
This information is offered in good faith and is believed to be accurate at the time of its preparation, but is offered without warranty of any kind, either express or implied as to merchantability, fitness for a particular purpose, or any other matter. SPI accepts no responsibility for any loss or damage arising from its use. SPI strongly recommends that you seek separate counsel for guidance to the accuracy and appropriateness of the information contained.
Stanley Kaufman, Ph.D. is president of CableSafe Inc. He is a member of NEC Code-Making Panels 12 and 16. He is also a member of the NFPA Technical Committee on Electronic Computer Systems, which is responsible for NFPA 75, Standard for the Fire Protection of Information Technology Equipment; and the NFPA Technical Committee on Telecommunications, which is responsible for NFPA 76, Standard for the Fire Protection of Telecommunications Facilities.