Grounding and Bonding in the Telecommunications Industry
When it comes to grounding and bonding, opinions and perspectives number like stars in the sky. To understand these topics properly in the context of U.S. electrical systems and telecommunications cabling, it is important to separate fact from fiction and be familiar with associated codes, standards, and industry guidelines.
Grounding and Bonding Hierarchy
- National and local electrical codes provide standards for safe electrical wiring and equipment installation. Bonding and grounding recommendations communicated in other standards and guidelines do not supersede national or local electrical code requirements.
- Accredited standards cover electrical system and telecommunications cabling infrastructure requirements, including bonding and grounding design, basic principles, and components for buildings of differing designs and structures.
- De facto industry guidelines are adopted by many companies and local governments, with respect to grounding, bonding, and associated site design parameters.
Defining Grounding and Bonding
The referenced examples of standards and industry guidelines include definitions which help answer basic questions such as “What is a ground?” and “What is bonding?”
- A ground is “a conducting connection, whether intentional or accidental, between an electrical circuit (e.g., telecommunications) or equipment and the earth, or to some conducting body that serves in place of earth,” according to NFPA 70, National Electrical Code (NEC).
- The act of bonding is “the permanent joining of metallic parts to form an electrically conductive path . . .” (source).
- A bonding network is a set of interconnected conductive structures that provide a low impedance path for the associated telecommunications infrastructure.
The Basic Founding Principles of Bonding and Grounding
Three basic founding principles for communications grounding are Equalization, Diversion, and Coupling.
Equalization involves minimizing voltage potential differences to the extent possible when dealing with very large energy from lightning sources. Given the inductance of a certain length of wire, the induced voltage is increased when the length increases. At lightning voltages this can be significant, regardless of what size wire is used for bonding.
Good practice is to use larger gauge and shorter length bonding conductors in a direct path, decreasing susceptibility to higher voltages. An example of how equalization is implemented by American Products is the use of internal ground systems in shelter products. Typically shelters have a Master Ground Bar (MGB) implemented per Motorola R56, ANSI, and other industry standards. From this MGB circling the internal shelter perimeter, a ground ring system can be provided. This “halo” ground system includes H-tap hardware along the wall bonding conductive elements, such as HVAC vents, with the intent of equalizing elements to the same ground potential for safety.
Diversion involves the redirection of unwanted transient energy away from areas and conducting paths normally used for communications. Communications paths must be established for information payloads to enter/leave a site to access equipment and perform normal functions. However, these same paths also represent an exposure with regard to unwanted hostile energies.
By properly designing and locating bonding network elements and grounding systems, transient energy largely will be diverted away from communications paths. An example of implementing diversion by American Products is the use of external ground bars. A cabinet or shelter can have a ground bar added with a low impedance bond to the internal MGB. The external ground bar provides customers the opportunity for direct connection to external site grounding systems and the connection of grounding elements, such as cable shields coming from a nearby tower, to the ground system outside the enclosure. This helps divert transient energy away from the communications equipment inside.
Coupling should also be considered in communications systems protection because of the principle of induction. Two conductors are inductively coupled when they are configured in such a way that a change in current through one conductor induces a voltage across the other. The magnitude of this induction is directly proportional to the conductor spacing. Therefore, to the extent possible when designing sites, the proximity of communications and bonding/grounding conductors to each other should be completed to minimize undesirable coupling.
Safety of personnel and protection of sensitive electronic equipment from ground faults, lightning, ground potential rise, electrical surges, and power quality anomalies is of utmost importance at any communications site. Though lightning and power surge electrical events cannot be prevented, proper communications grounding system design and installation may help minimize damage caused by these events.