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Archives
 November 1999 Issue
Features
NEC '99 Eclipses Previous Electrical Codes
By Jonathon Kramer
Just a few short years ago, the thought of measuring 90 V on a subscriber's drop would send chills down the spine of any field technician. A first thought might likely be, "Okay, how did the sub's tap fail?" Today, the same tech might say, "Cool! A telephony sub!" How times change.
While the technical platforms that drive our cable systems have rapidly evolved to support telephony and data services, the National Electrical Code (NEC) rules governing subscriber installations in most U.S. communities have been slower to keep pace with our technical developments. Moreover, once new rules are added to the NEC, the adoption of those new rules at the local government level often proceeds at little more than glacial speed. Many governments are just now getting around to adopting the 1996 NEC.
For the past 30-plus years, cable TV system drops and in-building cable system wiring have been governed by the ever-expanding NEC Article 820, titled, "Community Antenna Television and Radio Distribution Systems." In the newest edition of the NEC, the code authors have added an entirely new section, Article 830, titled, "Network-Powered Broadband Communications Systems."
Let's explore some of the similarities and key differences between our old friend, Article 820, and the new kid on the block, Article 830. We'll presume that your local government has adopted the 1999 NEC as its electrical code. (But beware. Your local government may be using an older version-see "But the Code Says I Can!" Part 1.)
Some new terms
When dinosaurs roamed the earth (that is, before the release of the 1999 NEC), we didn't have NEC definitions to describe the key elements of modern broadband networks. Section 830-2 of the new code offers some helpful definitions of the brave new world we've entered:
"Network Interface Unit (NIU). A device that converts a broadband signal into component voice, audio, video, data and interactive services signals. The NIU provides isolation between the network power and the premises signal circuits. The NIU may also contain primary and secondary protectors."
"Network-Powered Broadband Communications Circuit. The circuit extending from the communications utility's serving terminal or tap up to and including the NIU."
The first definition certainly seems to cover just about everything we could conceivably want to carry to and from our subscribers. As for the second definition, if you don't mind, I'll continue to call it "a drop" rather than a "network-powered broadband communications circuit."
Good news-you know most of it
Here, the "it" is Article 830. That's because the new article is based on (and in many cases copied directly from) Article 820. Most of the extensions that differentiate Article 830 from Article 820 flow from the logical outgrowth of sending more than 60 V at an appreciable current level down a drop and into a subscriber's structure.
The same basic on-building installation techniques apply under both articles. Likewise, the requirement that you must use listed drop cables is found in both articles. A limited exception to the listing requirement in Article 830-5 permits the use of some unlisted coaxial cables that were installed before January 1, 2000. Thereafter, you'll have to ensure that you use drop cables specifically listed for use on network-powered broadband communications circuits.
You'll also find in both articles requirements that you use special fire-resistant jacketed cables when you install them in air plenums and firebreak areas.
The drop grounding requirements of both codes are nearly identical, but in an interesting twist under Article 820-40(a)(3), the ground wire must be no smaller than 14 gauge, with no limitation of the maximum wire size. Under Article 830-40(a)(3), the minimum wire size remains 14 gauge, but the maximum wire size need not exceed 6 gauge, regardless of the maximum shield current that might be encountered.
Better news-you get to learn more
Under Article 830, the in-building wiring after the NIU must comply with NEC Article 800, which "... covers telephone, telegraph (except radio), outside wiring for fire alarm and burglar alarm, and similar central station systems; and telephone systems not connected to a central station system but using similar types of equipment, methods of installation, and maintenance."
In case this seems a bit too straightforward, the NEC Handbook explanation of Article 800 says, in part:
"Although information technology equipment systems are often used for or with communications systems, Article 800 does not cover wiring of this equipment. Article 645 provides wiring requirements for wiring contained solely within an information technology equipment (computer) room. See Section 645-2 for the definition of information technology equipment room. Article 725 provides wiring requirements for wiring that extends beyond a computer room.
"In some cases, the telephone system wiring is also used for data transmission; this use is covered by Article 800."
The bottom line is that once you install an NIU at a subscriber's structure, the body of NEC rules you must follow expands dramatically.
Let's move on to the some of the other key differences between Articles 820 and 830.
Who's calling, please?
Section 820-4, titled "Power Limitations," says that you can use coaxial cable to "... deliver low-energy power to equipment that is directly associated with the radio frequency distribution system if the voltage is not over 60 volts and if the current supply is from a transformer or other device that has energy-limiting characteristics." This isn't going to help you if you intend to power an NIU at a subscriber's structure.
Compare Section 820-4 with new Section 830-4, also titled "Power Limitations," which deletes the reference to coaxial cable and permits you to send up to 150 V to the subscriber's NIU. These changes make sense, especially when you're using coaxial drop cable with embedded twisted-pair telephone wires. If you intend to ring your subscribers' telephones using your cable system power, plan on living under Article 830.
Subs will be subs
In a telephony environment where we're sending some serious voltage and current to the subscriber's NIU, an important consideration is, "How do we protect subscribers from themselves?" Specifically, how do we protect them from receiving a nasty little electrical surprise when they're holding a can of beer in one hand, standing barefoot in a puddle of water, and using a dull old pair of rusty pliers to saw through the drop so they can install their own splitters to add yet another outlet? Article 830-10, euphemistically titled "Protection from Damage," tells us at Section 830-10(i)(4) that for overhead drops:
"Network-powered broadband communications cables attached to buildings and located within 8 ft. (2.44 m) of finished grade shall be protected by enclosures, raceways or other approved means. Exception: A low power network-powered broadband communications circuit that is equipped with a listed fault protection
device, appropriate to the network-powered broadband communications cable used, and located on the network side of the network-powered broadband communications cable being protected."
Either we can protect voltage-carrying drops in suitable enclosures, or we can use a fault protection device at the tap end of the drop to cut off the voltage in the event of "an unfortunate subscriber experience." Hey, this section might even save the necks of some of our own installers.
How high is high? How deep is deep?
We have relatively few drop height rules under Article 820 and virtually no drop depth rules. Most of the rules that that control cable TV drop installations before the drop reaches the subscriber's structure are found in the National Electrical Safety Code (NESC) or in state-level codes often set by state public utility commissions (PUCs).
Article 830-10 ("Aerial Cables") adopts the NESC cable standards for drops. Generally, drops must be no less than 15.5 feet over roadways, at least 11.5 feet over driveways where trucks don't venture and no less than 9.5 feet over pedestrian-only areas. The same article also sets a general climbing space requirement on the pole of no less than 24 inches.
As for direct-buried drops, under Article 830-11, most will have to be buried at least 18 inches below grade, with a few exceptions that will permit 12-inch depths.
Why did the code-writers adopt formal spacing and burial rules? The NEC's "Fine Print Note" for Article 830-10 says it all: "Network-powered broadband communications systems contain sufficient energy to shock and kill. For that reason, they are subjected to requirements similar to those for other high-powered circuits."
Wrapping up loose ends
A question sure to be raised is, "How do I know whether to apply NEC 820 or NEC 830 rules?" The simple answer is that if you (a) just use your plant to send broadband video or over-the-cable Internet services, and (b) you don't send more than 60 V down the drop, you're going to fall under the rules of Article 820. Once you send more than 60 V down a drop or install an NIU, you've moving up to the world of Article 830 (and Article 800, and maybe Articles 645 and 725).
A follow-up question: "Can my system fall under both Articles 820 and 830?" It's more than likely. Most of your subs (at least for now) won't subscribe to drop-powered telephony services that require you to install an NIU, so you'll install your cable TV and cable Internet subscribers under Article 820. Only those subs that take telephony services through an NIU will be installed following NEC 830 rules. Only in rare cases, such as when you're only installing Internet-over-cable to and through a computer room, will your system also fall under Articles 645 and 725.
Finally, "How do I get a copy of the NEC code?" First, ask your local electrical inspector what NEC code year your community has adopted or if some other code applies. I strongly recommend purchasing the NEC Handbook on CD-ROM for ease of searching and printing. The Handbook, whether purchased in book form or on CD-ROM, contains the entire text of the 1999 NEC, along with all of the notes and a tremendous amount of explanatory commentary not found in just the NEC. Many technical and most construction trades bookstores carry or can order the current NEC code book, Handbook, or Handbook CD-ROM. You also may purchase NEC materials directly from the National Fire Protection Association by calling or if you're outside the United States.
When it comes to knowing and applying the NEC to your system, it's not who you know, but what you know (and what you can show to your local inspector). It pays to know your code!
How are NEC Rules Made?
The 1999 National Electrical Code (NEC) traces its roots back to 1897 when the first national electrical code was published by the National Board of Fire Underwriters. Today, the National Fire Protection Association, a private nonprofit open-membership organization, oversees the development of the NEC. Based on public input from its members, including governments, manufacturers, installers and users, the code-making panels of the NEC recommend new or changed rules to the full membership of the NEC (typically once every three years). Once the NEC rules are adopted by a vote of the NFPA membership, they are published and made available for local, state and federal government agencies to adopt as their own electrical code. Governments in other countries also look to the NEC to provide the rational basis for those foreign government electrical codes.
"But the Code Says I Can!" Part 1
I frequently point out to system operators that they may be violating a provision of the locally-adopted electrical code, based on the National Electrical Code (NEC), for one reason or another. The most common retort I hear is, "Yes, but under the newly-issued NEC rules, we're allowed to ...."
The NEC is crafted and issued by a private organization and may sometime later be adopted by the local government agency responsible for electrical code enforcement. The key words here are "may" and "sometime later."
Most governments do not automatically adopt the most current NEC version upon publication. In fact, it's common to see a local government adopt the NEC from two cycles back (six years!). This might well mean that although you can get your hands on the 1999 NEC today, your local government might just now be getting around to adopting the 1993 code.
If you're relying on using Article 830 for the installation of telephony services, you might be in for a "severe shock" when the local electrical inspector says, "Hey, stop it! You're not permitted to send 90 V down a drop!"
So, what NEC code year has your government adopted?
"But the Code Says I Can!" Part 2
Even if your local government has adopted the 1999 National Electrical Code (NEC), one sure-fire way to instantly lose a code argument with a local inspector is to say, "Our company's NEC consultant says that the rules clearly require you to allow us to .&" The 1999 NEC code contains the following language (only slightly changed over the past 30-plus years):
"This Code is intended to be suitable for mandatory application by governmental bodies that exercise legal jurisdiction over electrical installations and for use by insurance inspectors. The authority having jurisdiction for enforcement of the Code will have the responsibility for making interpretations of the rules, for deciding on the approval of equipment and materials, and for granting the special permission contemplated in a number of the rules."
In essence, this rule (found in the 1999 NEC at Section 90.4) makes it clear that the intent is that the code be locally interpreted by the adopting government agency (usually the city or county government) and that final authority for approval of equipment and materials, and the granting of special permissions, rests with that authority. Although the NEC has many "Fine Print Notes" to explain the code, those explanations are only advisory, rather than binding upon the local government adopting the code.
That's why it's always best to educate your local code inspectors and officials regarding important elements of the code. The local inspector already is your judge and jury-don't let him become your executioner.
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Bottom Line: NEC '99 Changes
Cable's evolution from a simple delivery conduit for entertainment video into a sophisticated "fat pipe" for video, data and telephony generated pressure to update the primary regulatory safety code that governs cable subscriber installations.
We've learned that the 1999 National Electrical Code (NEC), which will be adopted by a majority of local governments over the next few years, will change and upgrade the techniques we employ to install subscriber drops, network interface units (NIUs) and associated equipment. We've also visited some of the more common ways a cable operator can run afoul of the new rules.
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Jonathan Kramer is a senior member of the Society of Cable Telecommunications Engineers, a member of the International Association of Electrical Inspectors, and a director of the National Association of Telecommunications Officers and Advisors. His Web site is www.cabletv.com.
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