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This article originally appeared in Cabling Business Magazine--

NEC Chapter 8, Communications Systems-1


By David Herres


This is the first of a four-part series dealing with National Electrical Code (NEC) Chapter 8, Communications systems. Each piece will examine one of the four articles within that chapter: Article 800, Communications Circuits, Article 810, Radio and Television Equipment, Article 820, Community Antenna Television and Radio Distributions Systems, and Article 830, Network-Powered Broadband Communications Systems. Article 800, Communications Circuits, is the longest article in Chapter 8, and provides groundwork and an overview of the rest of the chapter.-

The National Electrical Code, currently revised and re-issued by the National Fire Protection Association (NFPA) every three years, has no legal standing on its own, but is made available to states, municipalities and countries so that they can enact it into law if they desire. It has acquired almost universal acceptance in the U.S. and increasing influence worldwide. Many professionals beloieve it is not applicable under certain voltage or power limitations, but that is not the case. Even non-composite optical fiber, which carries no eloectrical current, can present a fire hazard when installed improperly, as when firewalls are drilled and not sealed correctly or when the sheathing material adds to fire loading, propagation and smoke generation,

In regard to "Communications Systems," voltage and power levels tend to be lower than power and light wiring, but that is not always true. Radio and television transmitters, for example, can involve voltages over 350 between conductors. Article 800, Communications Circuits, begins like other NEC articles with a statement of scope followed by definitions specific to the article. These definitions are in addition to those found in NEC Article 100, which is applicable to the entire Code. As for scope, Article 800 covers communications circuits and equipment. It does not deal with internal wiring in factory-made equipment, such as a television set, nor does it cover utility-owned equipment upstream from a utility-designated point of connection.

Certain communications related aspects are covered outside this article. Installation requirements for information technology equipment and systems in a telecom room are in Article 645 which, where the installation qualifies, offers less stringent requirements.

Remote Control, Signaling and Power-Limited circuits are covered in Article 725. Some of these requirements are tighter, as in circuits whose failure could present a safety concern, and some are less stringent, as when lower voltage and power levels are involved. Also outside the Communications Circuits articles are Fire Alarm Systems, covered in Article 760, installation requirements for optical fiber and raceways, covered in Article 770 and Network-Powered Broadband Communication Circuits, covered in Article 830. Everything else that has to do with communications circuits and equipment will be found in this nine-page article and in the other Chapter 8 articles.

Eleven definitions constitute the rest of the prologue to this article, and the first of these opens up what is becoming an enormous issue in the lives of cabling professionals. Abandoned communications cable is defined as "installed communications cable that is not terminated at both ends at a connector or other equipment and not identified for future use with a tag." This definition seems innocuous, but later in the article, like the resolution of a theme in a classical symphony, comes the climactic element: The accessible portion of abandoned communications cables shall be removed.

The reason behind this enormously labor-intensive requirement is clear. Consider a commercial occupancy where there may be frequent tenant turnovers. Workstations with varying connectivity requirements are shifted in the course of remodeling and new Ethernet, telephone, video and other cabling is put in place. Fire loading increases to the point where even a small, quickly contained fire can generate huge amounts of toxic smoke. For this reason among others, it is crucial to remove abandoned communications cabling in a timely fashion.

Parallel requirements are in place for other types of abandoned low-voltage cabling such as optical fiber, fire alarm and coaxial cable. Interestingly, there is no such requirement for power and light wiring with certain limited exceptions, notably wiring in cellular metal floors, underfloor raceways, information technology equipment not in metal raceway and temporary wiring.

Notice that only accessible cabling has to be removed. If it is in raceway, it is not accessible and can stay. Cable within a raceway can be more easily removed and can, in fact, at a future upgrade be used as a pull rope to install UTP with a higher Category number or even optical fiber. The fact is, however, that much abandoned communications cable has been installed outside of raceway. The job of removing it can be costly, largely because it has to be traced and determined not to be active. The risk of taking down a working system is always present. In view of this Code requirement, cabling designers and installer need to ascertain the scope of the job when doing new work and come to an agreement with tenants and building owners in regard to who is going to finance this Code mandate.

Another important Article 800 installation issue is that firewall openings must be fire-stopped to maintain the fire resistance rating. Wall boxes on either side of a firewall must not be directly opposite. Local regulations will mandate a horizontal separation, typically 24 inches. Section II of Article 800 deals with outside wires and cables, including where they enter a building. Before engaging in this type of work, it is necessary to review the relevant Code sections so that the final installation is fully compliant. There are requirements regarding separation from power and lighting conductors, and provisions for climbing space and roof clearances which vary according to roof slope and other conditions.

Besides the National Electrical Code, ANSI-C-2-2007, National Electric Safety Code, contains safety rules for overhead lines. Similarly, there are Code mandates for underground work. Raceways, hand-hole enclosures and manholes containing power and light, Class 1 or non-power-limited fire alarm circuit conductors must be meticulously designed and constructed so that these higher voltage and power levels do not energize your low-voltage cabling.

Section III of Article 800 covers the large area of circuit protection, which is accomplished largely by means of primary and secondary protectors.

A listed primary protector mitigates two dangerous conditions: accidental contact with higher voltage and power levels of electric power and light wiring and exposure to lightning. (An actual strike is not the only hazard. Lightning activity some distance away can induce dangerous voltage transients in communications cabling). These dangers are largely countered by the installation of a primary protector. It should be located in, on or immediately adjacent to the building close to the point of entrance. It cannot be within a hazardous (classified) location or near easily ignited material.

Part IV of Article 800 deals with the important topic of grounding. The NEC has a lengthy Article (250) on grounding, which is complex but central to all installations. Cabling technicians should devote significant time in delving into this subject to the extent required by the type of work being contemplated. The section on grounding within the Communications Circuits articles is only about one page long, but it makes extensive reference to the 30-page Article 250 and presupposes knowledge of it.

What has to be grounded? The primary protector and any metallic members of the outer sheath, as in coaxial cable, must be grounded. It is the responsibility of the cabling technicians that this grounding occurs. Naturally any metallic raceways or enclosures must be grounded in accordance with general Code practice. AC-powered equipment in metal enclosures will be bonded back to the building's electrical service equipment by means of the equipment grounding conductor which is connected to the main bonding jumper at the service main disconnect, usually within the entrance panel.

The building electricians will have provided a fully compliant grounding system, which cabling technicians should verify. The most recent Code cycle enacted that at the time of electrical service construction, the electricians create an intersystem bonding termination so that other trades can connect their grounding conductors to it. This apparatus, which is not found in older buildings, can take various forms, such as a specialized terminal mounted on the outside of the building near where the service conductors enter, or a short copper wire emerging from the meter socket enclosure.

This introduces another key concept, which is that all ground systems must be interconnected and also bonded to any metallic water pipe and other large coductive non-current carrying bodies, which could become energized. This idea sometimes astonishes the homeowner who envisions lightning "spreading" to various parts of the building. Actually the interconnection functions to limit voltage differences and to effectively eliminate voltage rise and current flow where it is not wanted.

Accordingly, it is important that cabling installers, in grounding their work, do not create a "floating ground" which could initiate voltage potential difference, resulting in flashover and fire.

Certain other Article 800 grounding requirements are often not observed in the field. The grounding conductor must be insulated (not bare as permitted for a service grounding conductor), not smaller than 14 AWG and as short as practicable. In one- and two-family dwellings, it is not to exceed 20 feet. If the distance to the intersystem bonding terminal or other acceptable grounding point is more than 20 feet away, itr is necessary to drive a communication ground rod at the primary protector location, and then bond to the electrical service ground with 6 AWG copper, bare or insulated, solid or stranded.

Part V of Article 800 concerns Installation Methods Within Buildings. It is here and in Part VI that we find a number of requirements. It is important to comply with all of these from the point of view of safety and also to avoid rejection by an electrical inspector and subsequent costly rework. The good news is that these requirements are quite straightforward and confined to about four pages. A central concept in this area is cable hierarchy.

In the event of fire, a major cause of injury and loss of life is smoke inhalation. There are various environments within a building and some are more sensitive than others. The most sensitive, in regard to fire propagation and smoke generation, is the plenum, which includes ducts and other spaces for environmental air. Type CMP, communications plenum cable, is listed as suitable for use in these areas. It pertains to the composition of insulation and outer jacket. There are definite protocols governing how tests are to be performed by listing laboratories.

The second most sensitive application is riser, which is where the cable is listed as suitable for use in a vertical shaft or from floor to floor. Riser cable (CMR) has good fire propagation and smoke generation properties, but not as good as plenum cable. Riser cable is also considerably less expensive than plenum cable.

Plenum cable may be substituted for riser cable. There is a hierarchy of cable types with plenum at the top of the list and CMX, Limited-Use Communication cable, at the bottom, restricted to non-riser and non-plenum use in residential buildings only. Any given cable can be substituted for one that is lower on the list, but not for one that is higher.

If you were doing a very limited amount of cable installation, you could stock only plenum-rated communication cable and use it for all communications work. The complete hierarchy with permitted substitutions is found in Article 800 and other low-voltage aricles where parallel requirements are found.
--END--


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Books for electricians --

Here is a selection of the most significant electricians' books available online today, at the best prices around. Clicking on any logo provides access to reviews and ratings by electricians. A good place to start is with the 2008 NEC Handbook, which contains the complete text of the current code plus extensive commentary, diagrams and illustrations. Other books of interest for the electrician are available as well.

Low Voltage, Telecom, Fire Alarm Books --


HOME | Best Web Host | Question of the Week | Archived Questions | More Archived NEC Questions | Still More Archived Questions | Still More Archived Questions-2 | Still More Archived Questions-3 | Articles | Electrical Deficiencies | More Electrical Deficiencies | Electricians Tools | Online computers | Cybercorner | Electrician's License | Electronics Tutorials | Electricians' worksaving ideas | Electronic Theorems | Satellite Dish | Digital Cameras and Equipment | HTML Color Chart | Electronic Acronyms | Electronic Definitions | Electrician's Soldering Tutorial | Photovoltaic Power | Wind Power | Fire Alarm Basics | More Fire Alarm Info | Working with MC and EMT | Electricians' Color Code | Wiring Commercial Garages | Managing Your Emergency Lights | Lighting Design | Industrial Wiring | Wiring Ethernet | Residential Wiring | Low Voltage Wiring | PLC Overview | Electrical Troubleshooting Techniques | Using Loop Impedance Meter | Ten Common Grounding Errors |NEC and Low-Voltage Wiring | Raceway Protection and NEC | Working with Metal Raceway | Inductance and Characteristic Impedance | Understanding Capacitance | History of the Ethernet | Twisting Data Conductors | NEC Article 800, Communications Circuits | NEC Article 810, Radio and Television Equipment | NEC Article 820, Community Antenna and Radio Distribution Equipment | NEC Article 830, Network-Powered Broadband | Troubleshooting Submersible Well Pumps | Wiring Healthcare Facilities | First Edition National Electrical Code 1897 | Books for Electricians | Links

Next:The second part in this series will deal with Article 810, Radio and Television Equipment.

--END--

This site is created and conducted By David Herres, NH Master Electrician License #11335M

E-mail: electriciansparadise@hughes.net


HOME | Best Web Host | Question of the Week | Archived Questions | More Archived NEC Questions | Still More Archived Questions | Still More Archived Questions-2 | Still More Archived Questions-3 | Articles | Electrical Deficiencies | More Electrical Deficiencies | Electricians Tools | Online computers | Cybercorner | Electrician's License | Electronics Tutorials | Electricians' worksaving ideas | Electronic Theorems | Satellite Dish | Digital Cameras and Equipment | HTML Color Chart | Electronic Acronyms | Electronic Definitions | Electrician's Soldering Tutorial | Photovoltaic Power | Wind Power | Fire Alarm Basics | More Fire Alarm Info | Working with MC and EMT | Electricians' Color Code | Wiring Commercial Garages | Managing Your Emergency Lights | Lighting Design | Industrial Wiring | Wiring Ethernet | Residential Wiring | Low Voltage Wiring | PLC Overview | Electrical Troubleshooting Techniques | Using Loop Impedance Meter | Ten Common Grounding Errors |NEC and Low-Voltage Wiring | Raceway Protection and NEC | Working with Metal Raceway | Inductance and Characteristic Impedance | Understanding Capacitance | History of the Ethernet | Twisting Data Conductors | NEC Article 800, Communications Circuits | NEC Article 810, Radio and Television Equipment | NEC Article 820, Community Antenna and Radio Distribution Equipment | NEC Article 830, Network-Powered Broadband | Troubleshooting Submersible Well Pumps | Books for Electricians | Links


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