Communications systems and equipment installed in buildings must comply with the specific rules given in Chapter 8 of the NEC . Even though these systems typically operate at lower energy levels, improper grounding and bonding can result in severe consequences for equipment and property and present shock hazards. Article 770 and the Chapter 8 articles of the NEC provide unique and specific grounding and bonding requirements for communications system installations.
Grounding, in the simplest form, is the process of connecting an electrically conductive object to ground (the earth). Bonding is the process of connecting conductive objects together to establish continuity and conductivity. If a system or equipment is grounded, it is connected to the earth, and if objects are bonded, they are connected together to electrically become one potential, or as close to the same potential as possible. These two processes work in unison to provide safety for communications systems, equipment and property, as well as operational grounding and protective grounding functions.
There are important general grounding and bonding rules for the communications systems addressed in Chapter 8 articles of the Code . The rules are intended to protect people and property from electrical hazards in normal operation and minimize differences of potential during abnormal events, such as line surges or lightning. Lightning is an unpredictable force, so meeting the NEC requirements is the minimum plan against damage from natural and unpredictable events. A lightning protection system in accordance with NFPA 780 provides another degree of protection above the minimum grounding protection required by the NEC .
Communications system grounding electrode conductors must be electrically common to the grounding electrode used for the electrical power system for system, equipment and personnel safety. Article 800 (specifically Section 800.100) provides common rules specific to the grounding and bonding schemes for the communications systems covered in articles 770, 805, 810, 820, 830 and 840. These articles provide the specific minimum sizing requirements for grounding electrode conductors and bonding conductors installed for these systems. The minimum size conductors should be understood, along with specific rules that address bonding all grounding electrodes together to become one, electrically.
The reasons communications systems must be connected to the building power system grounding electrode are quite simple, yet such connections are not always made correctly. Using the same grounding electrode as the building electrical service keeps the conductive parts of communications equipment at or close to the same ground (the earth) potential in normal operation. In abnormal events, such as surges related to lightning strikes, the objective is to keep conductive parts of electrical power systems and limited-energy communications systems at the same potential as the potentials rise and fall. This minimizes the possibility of destructive flashover events within electronic equipment and between electrically conductive parts and equipment within buildings or structures. If the grounding conductors of a communications system are connected to an electrode separate from the building power service grounding electrode, a lightning event on or close to the building can cause conductive parts of equipment in the power system and the communications system to rise at different potentials, creating possible flashovers that can damage equipment or even cause a fire.
The 2020 NEC was revised with regard to the structure and usability of the communications articles. In previous editions, these articles included a very significant number of redundant requirements repeated within each article, including grounding and bonding rules. Article 800 now includes general requirements that apply to and are common between articles 805, 820, 830 and 840. Similar grounding and bonding rules are applicable to each article and address requirements such as sizing of grounding electrode conductors, installation of bonding jumpers, installation of grounding electrode conductors and more. Each of these articles provides reference to the grounding and bonding requirements set forth in either section 770.100 or 800.100, as applicable.
As a reminder, Section 250.94(A) contains a general requirement to install an intersystem bonding termination (IBT) at the service equipment of a building or structure served. An IBT is also required at each separate building or structure supplied by one or more feeders or branch circuits. It must be installed in a way that leaves it accessible for connection and inspection. Section 250.94(B) provides an alternative method for connecting grounding and bonding conductors of communications systems by use of a copper or aluminum busbar not less than ¼ inch wide by 2 inches thick and long enough to accommodate the required connections.
About The Author
JOHNSTON is NECA’s executive director of codes and standards. He is a member of the NEC Correlating Committee, NFPA Standards Council, IBEW, UL Electrical Council and NFPA’s Electrical Section. Reach him at [email protected].