October 1, 2008
Review and Preview
By Steven C. Johnson, Johnson Telecom
Cable operators have two electrical codes to comply with: the National Electrical Safety Code (NESC) and the National Electrical Code (NEC). The NESC covers procedures for installing cables in easements while the NEC deals with premises wiring. The NESC goes through a 5-year review cycle, while the NEC uses a 3-year cycle.
Every three years, NEC committees meet and discuss proposed rule changes. The next such meeting is scheduled in January 2009, to begin work on the 2011 NEC. The meetings are part of a public process that can be followed on the National Fire Protection Association (the parent organization to the NEC) Web site, www.NFPA.org.
The most recent edition of the NEC is the 2008 version. Every three years when the new versions come out, local jurisdictions generally adopt the new version and apply it to all types of electrical installations. Therefore, it is prudent to know what the changes are in new versions of the code in order that the operator complies with new provisions.
An article of a few pages can only begin to summarize even the applicable portions of the NEC. For further information or details on anything discussed here, refer to the code or the handbook, which has additional interpretive information.
Preview and process
Before jumping into the code changes for 2008, let's look at how the process is structured. Work on the 2011 code is beginning, so we can examine that schedule. The 2011 schedule is listed in Table 1.
TABLE 1: NEC revision cycle 2011 edition
Any interested party can file a proposal for the committee to review. Proposal forms are available in the back of the NEC 2008, electronically at the NFPA Web site, or on my Web site (www.JohnsonTelecom.com). The committee reviews and acts on the proposal at the Report on Proposals (ROP) meeting, and the proposal is accepted, rejected or accepted with modifications. After the committee meeting, a report is published.
Interested parties can file comments after reading the report, and these comments are addressed at the Report on Comments (ROC) meeting. The committee and NFPA staff make the final edits, and the NEC document is discussed and voted on by the NFPA at its annual meeting. The approved document is then published.
The NEC is divided up into 20 panels and a Technical Correlating Committee (TCC). The names of the members of each panel and the TCC are listed in the front of the NEC book. Each panel has specific articles of the code, which they oversee. Panel 16 has jurisdiction over the articles that are related to several cable and telecommunications industries. (See Table 2.)
TABLE 2: NEC articles and related industries
Chapter 8 (Articles 800, 810, 820, and 830) stands alone in the code. Other portions of the code do not apply unless specifically referenced within Chapter 8. The chapter does have numerous references to other sections such as definitions, scope, grounding practices, workmanship, etc. This aids the user working in these areas in finding the requirements that apply to these disciplines.
Article 770 on Optical Fibers does not have this distinction, and electrical requirements in all other articles of the code apply to fiber-optic installations, where appropriate. Generally, one would not be carrying high voltage, for example, on a fiber cable; thus, many requirements would not apply because of the characteristics of the services carried.
NEC 2008 changes
Panel 16 had a major project in 2005 to renumber the applicable sections of the code between the articles to improve consistency and to have the numbering consistent from article to article. The major project for NEC 2008 was getting consistency in the wording of similar requirements among the various articles.
Most of the changes in the 2008 code are in the category of edits and clarifications. In order to be consistent, for instance, the word "coaxial" globally was added to "cable" in Article 820 for clarification. A definition of "coaxial cable" was added to the General Section of Article 820: "Coaxial Cable. A cylindrical assembly composed of a conductor centered inside a metallic tube or shield, separated by a dielectric material, and usually covered by an insulating jacket."
Other changes include the following.
Power blocking: An addition was made to Article 820.15 Power Limitations to state that "power shall be blocked from premises devices on the network that are not intended to be powered via the coaxial cable." In other words, don't run power down a drop cable to a subscriber's TV set. The TV set won't like it, and neither will the subscriber.
Abandoned cables: Abandoned cables are defined in Article 820.2 Definitions as those not terminated at equipment, other than a connector, and not identified for future use with a tag. No specifics are given on the tag other than that it should be durable. A simple tag with an apartment unit number would be sufficient to designate an unused cable as reserved for future use to feed that apartment. In the interest of eliminating fire hazards, Article 820.25 requires "accessible portions of abandoned cables" to be removed.
Spread of fire: Article 820.26 requires cable installations to be done in a manner to not substantially increase the spread of fire. Holes drilled through fire-resistant-rated walls, partitions, floors, or ceilings shall be sealed using approved methods to maintain the firestop ratings. Local building codes should provide assistance in meeting this requirement.
Unlisted cable entering buildings: For a number of years, the code has allowed bringing outside, unlisted cable into a building if you go no more than 15 meters (50 feet). In 2008, Article 820.48 adds an exception for using unlisted cables in plenums and risers. The 50-foot allowance is acceptable in other environments, but no longer allowed plenums and risers.
Protection devices: Protection devices are now specifically allowed in Article 820.100(E) provided they do not interrupt the grounding system. Article 820.93(C) states that when protectors are used, they will be installed outside and as close as practicable (code-speak) to the point of entrance to the building. They are to be installed on either side or integral to the grounding block.
Intersystem bonding termination: Article 100 Definitions adds the concept of an "intersystem bonding termination" in 2008, which is defined as: "A device that provides a means for connecting communications system(s) grounding conductor(s) and bonding conductor(s) at the service equipment or at the disconnecting means for buildings or structures supplied by a feeder or branch circuit." The intent is to define a common grounding point that all users can connect to. Article 820.100(B)(1) requires the use of the intersystem bonding termination, when it is available.
For those installing cable to mobile homes, 2008 version should make the requirements more understandable. The intent of requirements did not change; they were just rewritten to be more readable.
2008: 820.106 Grounding and Bonding at Mobile Homes.
(A) Grounding. Grounding shall comply with 820.106(A)(1) and (A)(2).
(1) Where there is no mobile home service equipment located in sight from, and not more than within 9.0 m (30 ft) from, the exterior wall of the mobile home it serves or there is no mobile home disconnecting means grounded in accordance with 250.32 and located within sight from, and not more than 9.0 m (30 ft) from, the exterior wall of the mobile home it serves, the coaxial cable shield ground, or surge arrester ground, shall be in accordance with 820.100(B)(2).
(2) Where there is no mobile home disconnecting means grounded in accordance with 250.32 and located within 9.0 m (30 ft) from the exterior wall of the mobile home it serves, the coaxial cable shield ground, or surge arrester ground, shall be in accordance with 820.100(B)(2).
The italic "within sight from" provision was removed. It makes no difference on the cable side whether one can see the disconnect point. We are not concerned with quickly disconnecting the cable, which is a valid concern with power. Grounding within 30 feet seemed to be the key.
Additionally, we split up the long sentence (the underlined text) to make it more clear and readable. If there is no power equipment within 30 feet, ground it like you would a house. The intent is that if the service equipment or disconnect switch is less than 30 feet away from the mobile home, you bond at the service equipment or disconnect switch. If it is farther than 30 feet, you should ground at the mobile home either to the frame or to an acceptable grounding point from the list in Figure 1.
FIGURE 1: Acceptable grounding points (Courtesy of NCTI and SCTE)
Key legacy requirements
Support of cables: Since the 1996 NEC, aerial cable cannot be attached to electrical masts on homes per Article 820.44(C). The electrical mast can be used as one of the grounding options, but not to maintain clearance. Attachment of cables to an existing raceway is not permitted according to Article 820.133(2)(B).
Cable substitution table: The proper cable should be used for the application. It is, however, acceptable to use a higher rated cable in a lower rated application. With this in mind, Article 820.154(E) contains a table of permitted substitutions. (See Table 3.) The cable types are defined in Article 820.179.
TABLE 3: Article 820.154(E) coaxial cable uses and permitted substitutions
According to cable manufacturers, CATVX is no longer manufactured because of lack of demand. As the "Cable Guy" on Panel 16, I'm occasionally bombarded with jokes about CATVX being used to deliver X-rated content. (Who says code people don't have a sense of humor?)
Acceptable grounding methods: Article 820.100(B)(2) lists the following seven options for buildings with grounding means.
1. The building grounding electrode system (as described in 250.50)
2. The grounded interior metal water pipe within 5 feet of its point of entrance to the building (not recommended any more because of the proliferation of plastic water pipe)
3. The power service accessible grounding means, if any
4. The metallic power service raceway (acceptable for grounding attachment, but not for clearance attachment)
5. The service equipment enclosure
6. The grounding electrode conductor
7. The building grounding electrode
It is not acceptable to bond to any removable pieces such as enclosure lids. Do not interfere with another service's ground or bond.
If the building has no grounding means, driving an 8-foot ground rod is required. On a practical side, if the building has no grounding, consult with your supervisor as to whether it is safe to serve it.
Grounding conductor: Article 820.100(A) specifies the criteria for the grounding conductor. It must be insulated (although there is no requirement for the insulation to be green, as some believe), listed for the application, stranded or solid, and be copper or other corrosion-resistant conductive material. The size shall be 14 AWG or larger and be capable of carrying current equal to the capability of the outer conductor of the cable. The idea is that under a surge condition, the drop cable carrying the surge will burn up before the grounding conductor does. The conductor will not be required to be larger than 6 AWG, however.
Starting with the 1999 NEC, the maximum length allowed for the grounding conductor was 20 feet for single and two-family dwellings. The conductor must be run as straight as practicable and protected where exposed to physical damage. Grounding conductor characteristics:
3. Copper or other corrosive-resistant conductive material
4. Stranded or solid
5. Between 14 and 6 AWG
6. Current carrying equal to drop shield capability
7. Less than 20 feet in length
8. Run in a straight line
9. Physically protected, where necessary
What happens if the ground block is more than 20 feet from the building ground? If that is the case, the cable operator may drive an 8-foot ground rod within 20 feet of the ground block, but then is required to bond the ground rod to the building ground with 6 AWG (no length limit specified).
Grandfathering: Grandfathering is another issue that is often raised. As the code changes, there is no requirement to retrofit what is already existing. If it was installed according to code at the time, it is grandfathered until it is substantially changed. A drop disconnect/reconnect would not be considered a substantial change, but a drop replacement would be. At such time, the installation would be required to be brought into compliance to the most recent code. (See 20-foot grounding conductor rule.)
What lies ahead?
Each 3-year code cycle creates approximately 450 change proposals for the telecommunications articles.
This year, Panel 16 will have representation from the direct broadcast satellite (DBS) folks for the first time. Dish grounding falls under Article 810, and there are challenges to grounding properly, especially in high-rise apartment installations. How do you ground a dish installed on the balcony railing of a 10th floor apartment?
Got any suggestions for code changes? If you have ideas to improve the code or correct errors, please feel free to submit them or to contact me to discuss.
Steven C. Johnson is owner of Johnson Telecom. Reach him at Steve@JohnsonTelecom.com.
The best resources you can arm yourself with are the latest edition of the National Electrical Code or the National Electrical Code Handbook. The Handbook contains the code but adds commentary throughout to explain and interpret. Another resource that is near completion is the SCTE National Electrical Code Broadband Installation Compliance Guidelines.
Don't discard your older versions of the NEC, though. Not all municipalities use the latest (or even the same) version of the NEC. Municipal adoption of the latest NEC version often lags, sometimes by a year or more. Definitely check with the code enforcement folks in the municipalities in which you work to see which NEC version(s) they use. Those are the rules you have to follow, regardless of the existence of a newer version.