Practical considerations for complying with the 2017 NEC requirement for power over communications cable

Jan. 1, 2017
Designers, installers and users must balance codes and standards for the next generation of ICT infrastructure.

By Rick Foster, RCDD, TLT; Innovative Engineering Services LLC

Now that we have the new 2017 National Electrical Code (NEC) NFPA-70, the challenge for owners, designers, and installers is to figure out how to successfully apply this code in the field for power over communications cable (PoCC) applications.

While the NEC’s primary focus is on installation and safety, the first order of business is to establish cable performance requirements. For the purpose of this article, we define performance as the cable’s electrical characteristics (Categories), and subsequent ability to transmit data reliably and efficiently.

Until recently the information and communications technology (ICT) industry’s primary focus on the performance of communications cabling and connectivity was essentially how it supported the current and future data transmission capability of the IT infrastructure. Today, PoCC adds a new dimension. Now, the challenge for designers, users, and contractors is: “How do we balance traditional ICT performance attributes of data transmission and bandwidth, with the capability to carry power and still comply with the new 2017 NEC?”

Certainly, every project is different but a common thread in the initial design phase for today’s greenfield and retrofit projects is, “I don’t want to keep installing new cable in my facility as bandwidth demands increase and more powered networked devices are added.” In other words, “How can I ‘futureproof’ the cabling infrastructure for both higher-speed applications and the next generation of powered devices on the network?”

Several characteristics, listed here, contribute to the generation of heat within a cable bundle. In the design phase of a cable-installation project, steps that can reduce heat within the completed cabling run include specifying cables that will handle higher power limits, designing support structures and pathways that provide greater airflow, and requiring lower fill ratios for conduits. During installation, loosely grouping cables together to avoid tight bundles, evenly separating cables in trays, and considering smaller bundle sizes can be effective techniques.

So how does one respond to that? Typically we start by providing design options based on current and anticipated performance needs. Should I put in 10G copper cables? Are shielded cables a better option? Zone distribution? Run fiber to the desk? Hybrid composite fiber/copper cables? Passive optical LANs (POLs)? Category 8? What about manufacturers’ warranties? The list goes on …

After presenting potential design options, their tradeoffs and narrowing down to hard choices comes the big question: What is the cost to “futureproof”? The final decision on the “right” design option for futureproofing the project is often a judgment call based on price-versus-performance. With performance in focus, we now need to apply code requirements. Enter the 2017 NEC.

The September 29, 2016 Cabling Installation & Maintenance webcast “The 2017 NEC and Its Effects on Cabling Infrastructure for PoE” is another excellent treatise on what you need to know about the new NEC and cable performance defined by standards organizations. The October issue of Cabling Installation & Maintenance presented the article “Data/Comm Cables: What’s New in the 2017 NEC” authored by Dr. Stanley Kaufman. The article gave a thorough and detailed review of the significant changes and additions for simultaneously powering and sending data over small-gauge communications cables. At the conclusion of Dr. Kaufman’s piece, he states, “The 2017 NEC has taken a major step toward addressing the potential hazards of using data/comm cables for powering devices.”

In essence what the 2017 NEC did was put the ICT industry on notice that we now have to consider both the safe application of power and performance together as they relate to the cabling and IT infrastructure. Without oversimplifying the relevant sections of the new code, what follows is my distillation of a lot of information on key code-related topics that have been talked about over the last year and more.

The following perspectives on the 2017 NEC, presented in question-and-answer format, are for installers, designers, and users to consider. Hopefully they are useful insights to assist you in making better decisions for your next ICT cabling project.

Q1) What are the key sections in the 2017 NEC to consider for PoCC?

A1) The best place to start is with the Introduction to the NEC in Article 90-specifically, Article 90.1. It reads: “90.1 Purpose (A) Practical Safeguarding. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. This Code is not intended as a design specification or an instruction manual for untrained persons.”

Most of us would recognize the statement in this section about practical safeguarding but we often overlook the fact that the NEC is not intended as a design specification or training manual.

The following excerpt from the NFPA website, nfpa.org, added further clarification to its purpose: “The NEC addresses the installation of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways in commercial, residential, and industrial occupancies.”

So, what is a fundamental element of the NEC we must consider around practical safeguarding? Installation practices.

Q2) Why does this revision of the NEC address PoCC and not previous editions?

A2) In past editions of the NEC, applying low levels of power over communications cabling did not present a safety concern. Today, with new powered devices and technologies such as Power over Ethernet (PoE), low-voltage LED lighting and suspended-ceiling power distribution, higher levels of power are applied over smaller wire gauges typical of LAN communications cables. This should not be a revelation to anyone in our industry.

A UL fact-finding report was commissioned to examine the impact of power levels and resultant heat that was generated over small-gauge communications cables never designed for power at these new levels. The 2017 NEC now defines the thresholds at which power and its attendant heat generation must be considered in cables from the point of view of safeguarding persons and property.

Additionally, setting limits on heating of cable conductors is not new to the NEC. The benchmark used to set such limits is called ampacity. The following is the NEC definition. “Ampacity. The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.”

Q3) Where can I find pertinent information in the 2017 NEC?

A3) In Chapter 8 Communications, installation guidelines are based on a power level ceiling. In Section 840.160 Powering Circuits, communications cables using 60 watts or less have no installation or bundle size restrictions. Over 60 watts, a threshold is crossed and the new table in Article 725 is referenced.

In Chapter 7 Special Conditions, Article 725 - Class 1, Class 2 & Class 3-Remote Control, Signaling & Power Limited Circuits, a new ampacity table has been added to Section 725.144.

The ampacity table establishes safety parameters associated with the smaller wire (26-22 AWG) gauge conductors for Class 2 and Class 3 4-pair UTP cables. The table takes into consideration cable temperature rating, wire gauge size, and ambient air, and sets limits on the permissible number of energized conductors.

Applying the table provides installation guidelines based on the maximum number of cables in a bundle above which overheating will occur.

It is important to remember that these critical thresholds were established by actual laboratory testing based on volts, amps and watts. Furthermore, testing was done under a reasonable worst-case bundle size of 192 cables. This condition could easily represent the “first 50 feet” of a typical telecommunications room (TR) rack supporting four, 48-port patch panels. Of course, as the cable bundle is distributed downstream cable counts are reduced in many instances.

Q4) Why is the NEC, and it seems everyone else, concerned about cable bundles?

A4) Cables that are bundled together cannot dissipate heat efficiently and will heat up faster than cables not bundled.

No surprise here. Rather than debate what a bundle is, because surely we will get multiple answers, let’s focus on how heat can be mitigated in a cable bundle. There are multiple options.

What can I do in the design phase? Some recommendations are to: specify cables that will handle higher power limits; design support structures and pathways that provide greater airflow; require lower fill ratios for conduits while managing code compliance.

What installation means and methods should be considered? Loosely group cables together and avoid tight bundles. Evenly separate cables in trays and consider smaller bundle sizes. Check the cable manufacturer’s installation guidelines for recommendations and limitations.

All the above are conventional techniques for reducing heat load, particularly above 60 watts. It should also be obvious that the new ampacity table requires close attention to bundle sizes. So is there a way to avoid “counting cables” or the added costs of closely supervising that bundle sizes remain compliant throughout the installation process?

Two options are presented in the 2017 NEC. First, the table gives derating guidance by allowing bundles to exceed the maximum cable count limit of 192, if necessary, under engineering supervision. Depending on the jurisdiction this may require approval by the authority having jurisdiction (AHJ). Good practice is to always engage the AHJ early in any instances where exceptions are permitted to be implemented.

Second, in Section 725.144(B) the 2017 NEC offers an optional cable design that is not a requirement but is quickly recognizable in simplifying installations by transcending bundle size and counting cables. That option is known as “LP” or limited power marked cable.

“LP” is an optional designation and mark that may be added to listed cable to attest that the cable fully complies with the NEC and has been further tested to not exceed rated temperature at the maximum current capacity of each conductor. The resultant “LP” suffix is shown on the cable. Example: CL2P-LP (0.5A), 23 AWG. In this example “LP” cable will meet safety requirements at 100 watts by not exceeding its temperature rating when installed under reasonable worst-case installation conditions mentioned above.

Like the previously mentioned option of engineering supervision, cable identified by, and marked with, the “LP” designation, permits installers and designers the option to simplify installation without restrictive bundle size, counting cables and cable separation schemes. Some contractors and designers see “LP” cables as the “easy button” to remedy these complexities.

Q5) Will the 2017 NEC require a licensed electrician to install these new types of high-power LAN cables?

A5) The NEC does not define what is required for an electrical license or who may obtain one. What the NEC does define is who is a qualified person.

In the 2017 NEC Article 100 Definitions, “Qualified Person” is defined as follows: “One who has the skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training to recognize and avoid hazards involved.”

There are three key points in this definition: skills, knowledge, and safety training.

A license is a legal credential. Electrical licensing or trade licensing is generally established by a government agency, normally at the state level. However, in some instances qualifications can be set or modified by local jurisdictions.

Licensing qualifications, requirements and testing criteria usually require the individual to prove work experience and competency. Recently safety training has been added to license requirements. Experience and knowledge can be in the form of apprentice programs, trade schools and hours of field work (OJT-on the job training).

Always check with local or state jurisdictions what the appropriate license or another legal credential is required before starting work.

Choosing any installer or installation company should be based on competency, experience and education.

Q6) Will the electrical building inspector fail installations if they believe future technologies or systems are not considered?

A6) It is unrealistic to expect an AHJ has that “crystal ball” of what future equipment or technologies will be put in place. So what is the AHJ role?

Let’s again refer to NEC Article 90 Introduction. Section 90.4 Enforcement gives the responsibility of interpretation and enforcement to the AHJ. Article 100 Definitions (page 70-31) defines: “Authority Having Jurisdiction (AHJ). An organization, office or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure.”

It is important to note that it could be an organization, office, or individual. In some projects, it could be more than one of those entities. There is also distinction between inspection and enforcement. Essentially one is a process, i.e. inspection; the other is a result, i.e. enforcement.

We previously established that at the core, the NEC is about installation means and methods. When an inspector or AHJ comes on site they are evaluating what has been permitted, what is in place and generally will examine and report on installation deficiencies.

If these are a result of improper design in their opinion, they will often engage with the engineer of record or permitee to resolve or clarify. The AHJ may also question products or devices that are new or unfamiliar to them. Although it may seem obvious, find out who the AHJ is for the project and engage with them prior to installation to see if they have any questions or concerns.

Q7) Does the 2017 NEC comment on the existing cable? Will the cable be “grandfathered” if I install new high-powered devices after initial installation?

A7) The NEC does not have the word “grandfathered” in its text. Responsibility for safety generally rests with all the building stakeholders-owners, tenants, engineers, contractors and installers. Our industry often deploys and changes out new equipment well past the initial installation, sometimes years later. What guidance did the NEC provide, if any, post-installation?

A new section was added: Section 725.121(C) Marking. This will require the maximum current and voltage output for each connection to be labeled. The effective date for this implementation is January 1, 2018 so that equipment manufacturers and testing agencies, as needed, can work together to define a workable solution without compromising equipment reliability.

What follows is a verbatim statement from the NEC Panel 3 Committee for that section.

Committee Statement on Section 725.121(C).This new section addresses the labeling of limited power circuit output connection points on listed IT equipment and listed industrial control panels and equipment. Bundling of large numbers of Class 2 conductors from IT servers and other similar IT and industrial equipment can create safety issues with very small current levels so having the output ports identified with the current and voltage rating is critical so the installer can connect the proper cable types. Labeling the output connections will permit the installer to have ready access to the current and voltage levels at the point of connection at the equipment, rather than internally within the equipment. The effective date was inserted to allow the manufacturers to comply with this requirement.

This new section takes into consideration that easily identifying those new levels will allow installers and owners to at least know what the equipment is outputting in the field on “Day 2.” With this information, it can be determined if the thresholds of the existing cable plant will handle the new equipment by at least reading the cable jacket and observing the installed conditions.

In summary

The combination of power and data transmission on the ICT infrastructure and its related components will continue to create new technologies and innovative products for our industry to help drive the installation of new IoT devices in the enterprise.

Engagement with the local AHJ early in the project to understand local requirements and to inform them if exceptions are to be implemented for approvals will avoid last-minute complications.

Means and methods to mitigate overheating of cables must be considered during the design phase and final installation practices of the ICT infrastructure.

“Futureproofing” the ICT infrastructure is no longer just about performance. To support these new IoT devices, next generation of systems and applications, we will need to understand how to balance both performance defined by standards and power defined by codes.

Rick Foster, RCDD, TLT, is director of IT infrastructure and commissioning services at Innovative Engineering Services, LLC (www.iesllc.biz). He has been in the structured cabling and IT infrastructure market since 1979 an dhas managed a distribution company, a design/build installation company, and a network integration firm. Rick holds a CT low-voltage electrical contractor’s license (C-5) and design license (TLT), and has served on various professional organization committees and panels, including NFPA, BICSI and the State of Connecticut.

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