Site power and grounding audits/evaluations of commercial and industrial locations routinely identify electrical power system grounding and bonding problems. According to S. Frank Waterer, an electrical engineering IEEE Fellow at Schneider Electric with more than 30 years of experience, approximately 70% of all anomalies, dysfunctions, or problems associated with power distribution systems are directly or indirectly related to bonding and grounding issues.
To maintain the safety of use and acceptable performance of connected equipment, we typically design and install grounding and bonding of the building structure (building steel) and certain conductive parts of these systems. In fact, we assume that safety grounding and bonding of the electrical power system and the load equipment are inherent parts of the design and installation so that both meet applicable codes and product safety standards. As electrical engineers, plant/facility electrical maintenance personnel, and electrical installers, this is part of doing business. However, this assumption can be risky.
Factors affecting performance
Ideally, properly designed, installed, and maintained electrical system grounding and bonding in a commercial building would suffice (via feeder and branch circuits) for connected electronic load equipment. In practice, however, economic constraints typically render the electrical installation as the lowest cost (lowest bid) endeavor required to meet the “safety” requirements of the applicable electrical code. Because the National Electrical Code (NEC) is not a design document, installation considerations prevail — at the expense of designing and installing for performance. Furthermore, even if design considerations were incorporated with safety requirements, other considerations would bring the adequacy of such an installation into question. For example, consider the following:
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Voltages (lightning and power faults) developed across electronic equipment interconnected across different floors of a building.
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Voltage offset (ground potential difference) between different power systems serving interconnected electronic equipment.
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Electromagnetic interference (EMI) filter currents on the equipment grounding conductors of the power circuits serving electronic equipment.
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Continuity of the power system(s) equipment grounding conductors and grounding electrode conductors (during damage from power fault, maintenance, accident, or other).
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Adequacy of power system ground-fault protection and overcurrent protection (for example, will breakers actually operate when they have not been exercised for years?).
To be sure, the efficacy of the power system equipment grounding system to serve as the single grounding reference for the telecommunications electronic equipment was thoroughly discussed during the formulation meetings preceding publication of TIA/EIA 607-1994. (See Telecom/IT Systems Convergence below.) Many aspects of the problem were considered before a recommended practice was determined — including the significant need for uniformity of application. (Note: Such activity on grounding and bonding to serve different industry sectors is not restricted to the telecommunications industry. For example, industry sectors serving building automation and industrial control systems routinely specify a distinct grounding and bonding system.)
In essence, a multi-tenant commercial building is expected to provide for grounding and bonding infrastructure in accordance with ANSI J-STD-607-A and IEEE Std 1100-2005, “Recommended Practice for Powering and Grounding Electronic Equipment.” Note also that these standards cover small commercial buildings whereby recommendations are somewhat scaled down for increased practicality.
Supplemental grounding and bonding components
Relative to the electrical power system, we can consider the major components shown in Fig. 1 (click here to see Fig. 1) as supplemental. The power system equipment grounding conductor serving the electronic equipment (placed into locations as shown in Fig. 1) is intended to provide the required safety ground (product safety). Other identifiable supplemental grounding and bonding entities at such a location may include:
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Additional connections to building steel.
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Additional “made” earthing electrodes such as rods/plates bonded to equipment grounding conductors (NEC 250.54).
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Surge protective devices (SPDs) during time of their operation.
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Additional equipment grounding conductors (insulated preferred) placed into the metallic conduits and raceways of the serving power system.
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Equipment bonding topologies, such as for multi- or single-point grounding (to be covered in Parts 2 and 3 of this article).
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A lightning protection system (LPS) installed to lower the risk of lightning and surge damage to the structure and its contents, which include electronic equipment.
Figure 2 (click here to see Fig. 2) illustrates how complexity enters into the application of supplemental grounding and bonding entities. It is a limited illustration and does not show all components (such as the AC power distribution wiring and its grounding and bonding). The complexity identified is the use of one versus two ground rings. Suppose Ground Ring 1 was previously installed as recommended in IEEE Std. 1100-2005 for promoting intersystem bonding of multiple service provider systems into the building. In doing so, the NEC “takes over” the ground ring, and it becomes part of the grounding electrode system (GES) for that building. For the LPS, the NEC defers to NFPA 780-2004.
Interestingly, Clause 4.13.1.3 in NFPA 780-2004 requires the grounding electrodes for the LPS to be separate entities from the building (electrical) grounding electrode system. Where real estate is scarce, one can envision Ground Ring 2 for the LPS being placed very close to the pre-existing ground ring for the GES and bonded to the electrical ground ring. This seems to be a perplexing juxtaposition of two needed codes/standards. (Why can't one ground ring suffice when in such close quarters?) You can imagine the confusion at such a job site. Now, add to that confusion the fact that neither ground ring is considered supplemental by its controlling code or standard.
This complexity illustrates that “supplementing” the NEC required GES with additional grounding and bonding entities, which are not considered by their controlling standard to be supplemental, requires careful consideration.
Supplemental grounding and bonding infrastructure entities
The discussion here will not address technical development. For further technical information, refer to IEEE Std 1100-2005 and similar documents.
Supplementary grounding electrode
Section 250.54 of the NEC permits a grounding electrode to be connected to an equipment grounding conductor, as described in 250.118. Essentially, this allows for localized earthing to hold the electronic equipment ground to the same value as the local ground nearby that equipment. You can consider this application as an added value for safety grounding (voltage equalization) at or nearby the equipment. However, the NEC doesn't mention EMI considerations for this application. As the terminology implies, the NEC considers this application only as a supplement to all other grounding and bonding requirements that apply. The supplementary grounding electrode should never be used as the sole grounding means for the equipment.
Lightning protection system (LPS)
Generally, there is little argument for not using a properly designed and installed LPS where risk analysis indicates the need. The LPS grounding and bonding is supplemental relative to the electrical power system GES in a commercial building. Generally, the LPS can serve to keep the majority of the lightning current from dissipating within the building. The positive benefits are obvious — fire protection of the building and its contents (including electronic equipment). Regrettably, some negative issues may also arise. Consider a bonding conductor placed from an LPS down conductor to a metal object within the arcing area of the down conductor (formula given in NFPA 780-2004). Such bonding prevents a side flash to the metal object. However, it also extends the lightning voltage to the bonded object. Thus, a new concern arises over the arcing area to metal objects in proximity to the first metal object. Conceivably, the lightning voltage could be “bonded” deep into the building, which is one reason electronic equipment shouldn't be located near conductors carrying lightning currents.
Additional equipment grounding conductor (preferably insulated — green wire)
This supplemental grounding and bonding entity has provided countless benefits since its inception in the 1960s and is highly recommended as a standard practice. Excellent technical validation is contained in IEEE Std 142-1991, “Recommended Practice for Grounding of Industrial and Commercial Power Systems” (Green Book), IEEE Std 1100-2005, and the International Association of Electrical Inspectors' “Soares Book on Grounding,” Edition 9. The green wire concept is so vital that recognized industry documents mandate or “strongly recommend” the use of a green wire. Prime examples are Telcordia generic requirements documents (GRs), ANSI T1 standards, and numerous ITE power quality guidelines. But even with the green wire, you must not relax the bonding and grounding requirements for the metal conduit or raceway (which is also an NEC requirement). Over time, even initially and properly installed metal conduit and raceway can sometimes be found in an “unbonded” condition at one or more locations. Until repairs are made, the green wire serves an invaluable backup function. The green wire definitely promotes the operation of circuit protective devices to remove the voltage to the faulted circuit in a timely manner. In so doing, the fault current has less time to influence the operating performance of electronic equipment. The green wire also contributes to the EMC functionality of the electronic equipment due to its EMI filters being referenced to equipment ground. Note that for non-metallic conduit and raceway, the green wire function becomes a requirement and is no longer considered supplemental. Figure 3 (click here to see Fig. 3) shows the green wire in a standard circuit and also in an isolated (insulated) grounding receptacle circuit (IGR).
Taken to another level, yet another insulated green wire provides a so-called “isolated” function for the isolated (insulated) grounding receptacle circuit described in the NEC. In this wiring configuration, the IG green wire is not supplemental because it is the only equipment grounding conductor available at the outlet for connection to the electronic equipment. However, the “regular” green wire in the same circuit is installed as a supplemental grounding and bonding conductor to the metallic conduit or raceway. The IG green wire can be carried all the way back to the serving power source within the same building before being grounded. Purportedly, this arrangement provides a “non-influenced” ground reference for the connected electronic equipment. Despite good intentions, this circuitry can bring unexpected problems that may be worse than those purportedly cured. IEEE Std 1100-2005 provides excellent critique on this circuit. Generally, such a circuit is not recommended. Figure 4 (click here to see Fig. 4) shows how the IGR circuit can be subjected to induced currents by interconnected electronic equipment.
ANSI J-STD-607-A
This supplemental infrastructure should be viewed as a single entity. Telecommunications is intended to account for any electronic equipment. Industrial electronic equipment is not specifically addressed. Generally, this infrastructure is intended to:
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Provide a uniform grounding application known and expected by the building owner, tenant and equipment supplier.
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Follow the pathways and spaces (ANSI/TIA/EIA 569-B-2004) corridors provided for information technology and telecommunications cabling systems.
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Be readily identifiable and accessible at (equipment) rooms.
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Be administered under ANSI/TIA/EIA 606A-2002.
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Last the lifetime of the building.
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Be distinct from but bonded (equipotential) to the serving electrical power system equipment grounding conductor(s) [typically panelboard(s)] at the room containing the electronic equipment.
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Be adequately sized to provide equalization and reduction of steady state and surge voltages between several consecutive floors (via TBB and GE) — equalization effectiveness is dependant on the frequency and magnitude of the equalizing currents (note that equalization is intended to reduce electrical stress on interconnected links of electronic equipment across several floors or adjacent TBB corridors); basis for the sizing is not readily apparent from the standard, as AC fault currents are not anticipated on the defined infrastructure. Presently, a maximum required size is 3/0 AWG as this size is also acceptable to control voltage drop on a nominal 48V telecommunications centralized DC power plant serving adjacent floors.
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Provide earthing reference from the TMGB to any TGB (via TBB) — reference dependant on the frequency of any currents on the TBB (note that electronic equipment on that floor may or may not need such reference).
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Provide additional information in Annexes on topics related to grounding and bonding.
Generally, this infrastructure is not intended to:
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Replace grounding and bonding required by the electrical power system (NEC and design requirements).
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Replace the need for “decoupling” of electronic equipment from other equipment served by a different (or too distributed) grounding system.
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Replace the need for “decoupling” of electronic equipment from other equipment served by a different power system.
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Replace the need for an LPS. Furthermore, the intended pathways location for the TBB is generally in a central corridor and away from components of the exterior LPS.
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Adequately control electromagnetic interference. For example, susceptible links may need to be decoupled or shielded.
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Dictate the choice of electronic equipment bonding topology desired by the equipment manufacturer or the user (such as a mesh common bonding network [MCBN] or an isolated [insulated] bonding network [IBN]).
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Replace the need for a shielded (or screened) cabling system.
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Function as an equipment grounding circuit to clear electrical system ground faults (due to intentional separation from power circuit conductors, the impedance to the TBB circuit severely limits current levels.
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Serve as an MCBN or signal reference structure grid for susceptible electronic equipment as described in IEEE Std 1100-2005.
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Serve as the grounding and bonding system described in ANSI/NECA 331-2004 Standard for Installing Building and Service Entrance Grounding. Indeed, this NECA standard recognizes ANSI J-STD-607-A-2002 and IEEE Std 1100-1999 (replaced by 2005 Edition).
Note that ANSI J-STD-607-A-2002 is not a panacea for power quality and electromagnetic compatibility (EMC) issues related to the electronic equipment. Even with its best feasible installation, this standard doesn't account for grounding-related issues such as surge protection and control of EMI.
This caveat is stated in the scope of the standard. However, you should intentionally coordinate the solutions to power quality- and EMC-related issues with the grounding and bonding infrastructure described in this standard. One of the hidden pitfalls in using this standard is the standard's bundling with the TIA suite of cabling standards. By bundling, the electrical and electromagnetic environments are assumed to be properly addressed alongside all other cabling issues. In reality, recognized subject-matter expertise is still required. Even so, this standard does promote uniform application requirements and recommendations that lessen the application skills needed for writing specifications on grounding and bonding for a commercial building. Considering the complexity involved in both understanding and properly applying grounding and bonding principles, the designer/specifier for telecommunications is well advised to fully apply the standard - knowing that the many complexities were entertained and addressed by subject-matter experts and the best compromise afforded (all things considered). Without this generalized approach, the application process can become unwieldy as a myriad of site variables must otherwise be tediously resolved.
Due to its lifecycle status and previously noted issues, a revision process is currently being launched for ANSI J-STD-607-A-2002. Many industry concerns are recognized for possible discussion. The scope of the document may be enlarged to include expanded coverage of grounding and bonding from the Telecommunications Main Grounding Bus Bar (TMGB) to the equipment unit; modern data centers as described in ANSI/TIA 942-2005; low-wide buildings; grounding between buildings in a campus environment; surge protective devices; and industrial circuit links used in a commercial environment.
In summary
Supplemental grounding and bonding for telecommunications and information technology equipment in a commercial building is based on proven historical development from the telephone industry. Coupled with industry-promoted supplemental grounding and bonding for electrical circuits (green wire) and a proper LPS, modern electronic equipment is more easily placed into a uniform and adequate grounding and bonding infrastructure within a commercial building, thanks primarily to ANSI J-STD-607-A-2002 and IEEE Std 1100-2005. However, don't confuse the application of ANSI/NECA 331-2004 or the NEC with ANSI J-STD-607-A-2002. The intent of the telecommunications grounding and bonding infrastructure is to “supplement” rather than replace (or be replaced by) electrical/lightning grounding and bonding codes and standards. This approach is harmonized to that taken in international telecommunications (ITU-T-K series) documents and European standards on earthing and bonding.
By following the Telecommunications pathways and spaces corridors (described in ANSI/TIA 569-B-2004), the grounding and bonding infrastructure is more “centralized” within the building. This location promotes decreased influence from lightning events and the larger power system fault currents. Above all, the “need for uniformity” of the grounding and bonding infrastructure must be honored. Next month we'll examine supplemental multi-point grounding and bonding topologies for electronic equipment.
Bush is director of research — power & grounding for Panduit in Tinley Park, Ill.
Sidebar: Telecom/IT Systems Convergence
This industry has historically recommended a distinct (but not isolated) grounding and bonding infrastructure since the earliest deployments of electronic equipment. Such recommendations were described in AT&T Bell Labs system practices (BSPs) and (after the 1984 deregulation of the telephone industry) by incorporation into Bellcore (now Telcordia) generic requirements (GRs) and ATIS Committee T1 national standards (ANSI T1.xxx). Such practice is industry-recognized for contributing to the reliability of the public telephone network.
With the convergence of telephone and computer technology now well realized, reliability of the same or similar systems in a commercial building is a similar concern. In the spirit of harmonization, the Telecommunications Industry Association (TIA) developed a distinct grounding and bonding infrastructure in its document TIA/EIA 607-1994, “Commercial Building Grounding and Bonding. Requirements for Telecommunications.” In 2002, ANSI J-STD-607-A, “Commercial Building Grounding (Earthing) and Bonding Requirements for Telecommunications,” superceded TIA/EIA 607-1994 and carried forward the same distinct grounding and bonding infrastructure.
