Equipment Grounding Conductors Research Articles

Appropriate Implementation of the Main Bonding Jumper and the Equipment Grounding Conductor: A Deeper Look Into a Suitable Ground Path

In many wye electrical systems, the function of the ground and neutral conductor is not differentiated because they are incorrectly joined. From a technical point of view, a connection between ground and neutral shall only be made once, at the main electrical panel; otherwise, those conductors should form two different paths. Although the implications of this connection are often seen as shallow and a misinterpretation of the National Electrical Code (NEC) makes it acceptable, this matter is actually very significant when it comes to protecting humans. Thus, it is important to take a deeper look into how to make a suitable ground path, which is the scope of this article.

The Equipment Grounding System as an Effective Bonding Topology for Telecommunications Environments

Bseing provided an adequate telecommunications bonding infrastructure is one of the primary concerns for telecommunications cabling designers and installers for new and existing installations. Although not considered a safety ground where ground-fault current is concerned, the telecommunications bonding infrastructure has importance where the components are intended to equalize potentials in the event of lightning, electrostatic discharge, electromagnetic interference, and other transient events that may be imposed on it, or within telecommunications spaces. Very recently, several telecommunications design groups with varying responsibilities for data center, military encryption, and commercial facilities have explored feasible options in providing an equipotential plane for their telecommunications bonding infrastructure, especially in locations where exposed metal frame of the building is not available; the most prominent of these options being the use of the ac equipment grounding conductor system due to the abundance of metallic surface area utilized for the ac premises wiring system. This article is intended to present field-testing data and draw technical conclusions from the same so as to verify whether the equipment grounding system is viable as an alternative bonding infrastructure plane that can achieve the same effect as the standard practices in place today.

New Generation Tester to Assess the Electrical Safety in Low-Voltage Distribution Systems

The determination of both magnitude and duration of touch voltages is of paramount importance to protect persons against electric shock hazards, such as those caused by basic insulation failure in equipment/appliances, or direct contact with live parts. The magnitude of touch voltages depends on the impedance of the equipment grounding conductor (EGC) (also referred to as protective conductor), which should be therefore properly sized. In the US, the National Electric Code (NEC) provides minimum sizes for the EGC; however, the NEC further clarifies that the EGC selected in the specific NEC table might need be sized larger to provide adequate electrical safety. In this paper, the authors discuss the major specifications that a “new generation” tester applied to NEC based low-voltage receptacles, or live terminals of feeder/branch circuits, should possess to indicate to users if a ground-fault would cause unsafe touch potentials. Such tester should also unequivocally identify improper wiring of the outlet (e.g., phase-neutral swap, EGC-to-neutral bond).

Detection of Poor Contacts in Low-Voltage Electrical Installations

Effects of a reduced torque on heating and the electrical resistance of wire-screw terminal connections in an old (used) receptacle and two new receptacles with intentionally corroded connections were experimentally investigated in the laboratory. In one of the new receptacles, the corrosion process was accelerated by treating the line connection with a mixture of nitric acid and hydrochloric acid, and in the other by treating the neutral connection with sulfuric acid. It was shown that by using these acids, both the temperature rise and electrical behavior of long-serving receptacles can be simulated. The possibility to detect a poor contact in an electrical circuit by measuring both the line to earth (L-PE) resistance and the line to neutral (L-N) short circuit loop resistance during a periodic verification of low-voltage electrical installations was also analyzed. In the laboratory conditions, a test electrical circuit with a poor contact in each of the tested receptacles was formed and the influence of that contact on both of the mentioned resistances was observed during long-lasting heating processes. Based on the results of both the laboratory experiments and periodic verifications of low-voltage electrical installations in public and commercial buildings with the total of 11 243 receptacles, a new procedure for detecting poor contacts in low-voltage electrical installations, valid for the terra neutral protection system, is recommended. The procedure, intended for periodic verification, provides information about poor contacts and their location in the tested receptacle (on the phase, neutral, and/or equipment grounding conductor) by comparing both the L-PE resistance and the L-N short circuit loop resistance to the limit values obtained during the verification.

Ground-Fault Protection of Personnel: The Field Applications of a Class C GFCI in a Crude Oil Refinery

Most Refineries, Drilling Platforms, and chemical plants are equipped with receptacles used for powering equipment. This can present a shock hazard; therefore, the National Fire Protection Association (NFPA) and Occupational Safety and Health Administration (OSHA) require ground-fault circuit interrupters (GFCIs) on all receptacle powering equipment used by personnel. However, these GFCIs are not part of the building?s permanent wiring. Due to the lack of GFCIs at voltages above 240 V, both the NFPA and OSHA require employers to implement the assured equipment-grounding conductor program for all temporary wiring installations.

Grounding: Bonding to Earth: We Leave Out Something Big When We Just Say \"Bonding\"

Returning to basics, grounding is bonding to earth. While grounding electrodes are the only true bonds to earth, the term "grounding" has been traditionally applied when bonding to extended conducting bodies such as the ground bus in an electrical panel. That tradition is presently under fire, with suggestions that what is referred to as the equipment grounding conductor (EGC) should be renamed the equipment bonding conductor. Beyond semantics, the term "bonding" alone compared to grounding (bonding to earth) presents a clear omission, which is the reference to earth. This article challenges that omission, presenting the multifaceted approach for the reduction of electrical hazards that is provided by bonding to earth rather than simply bonding.

Does Grounding Make a System Safe?: Analyzing the Factors That Contribute to Electrical Safety

Grounding is generally accepted as an operation to make systems safe. For grounded systems, the fault return conductor [sometimes called the equipment grounding conductor (EGC)] brings the potential at equipment enclosures to ground but only when there is no fault current. The potential rise due to the fault current flow can raise the potential to a hazardous level. It is shown that simple grounding does not provide for safe systems. The fault return conductor, grounded or not, and the overcurrent protective device, in combination, are the components that may prevent ventricular fibrillation and provide safer systems.

Ground-Fault Conditions in Low-Voltage Systems: Potential Differences Between Exposed Conductive Parts

In low-voltage systems, ground faults do not necessarily involve the actual earth, but fault currents may return to the source via conductors. Such conductors, which provide a clear path toward the source, are defined in the applicable codes and technical standards as equipment grounding conductors or protective conductors.

Thermal Sizing and Electric Shock Calculations for Equipment Grounding Conductors

This paper presents the thermal sizing procedure of equipment grounding (protective) conductors and the electric shock calculations as per the standard 60364 of the International Electrotechnical Committee (IEC) that is used worldwide. The application of IEC standards in the design of low-voltage systems (i.e., not exceeding 1 kV) governed by the National Electrical Code (NEC) and the American National Standards Institute (ANSI), which are adopted in the U.S., is discussed and proposed in this paper. The authors propose an interpretation of the NEC installations in light of the earthing definitions included in the IEC realm. On this premises, IEC sizing criteria are applied to typical North American installations to prove their general applicability and their legitimacy to NEC/ANSI-based electrical systems. Examples are also presented for both thermal sizing and electric shock calculation of equipment grounding conductors.

An Analytical Evaluation of the Factor $k^{2}$ for Protective Conductors

At the occurrence of phase-to-ground faults, abnormal levels of thermal energy I2t, due to the Joule effect, will be developed during the clearing time that protective devices take to operate. The I2t, also referred to as specific energy or Joule Integral, is accumulated within the elements forming the fault loop, such as the protective conductors (also referred to as equipment grounding conductors), responsible to return ground-fault currents to the source. As a consequence, the temperature of these conductors elevates and may exceed, in the case of an incorrect design, the maximum value that their insulation can withstand. This dangerous situation can cause the failure of the conductor insulation and/or trigger fires in neighboring materials. The maximum I2t that protective conductors can endure is, therefore, crucial in order to guarantee the electrical safety. The parameters on which the maximum I2t depends are described by the factor k2, which will be herein discussed and analytically evaluated. The intention of the authors is to provide a theoretical support to the Power Systems Grounding Working Group of the Technical Books Coordinating Committee IEEE P3003.2 “Recommended Practice for Equipment Grounding and Bonding in Industrial and Commercial Power Systems”; the working group is currently elaborating a dot standard based on IEEE Standard 142-2007, also referred to as the Green Book. To this purpose, a comparison with existing formulas, currently present in codes, standards of the International Electrotechnical Commission and of the IEEE, as well in the literature, will be also presented.

Contact voltage measured in residences: implications to the association between magnetic fields and childhood leukemia.

We measured magnetic fields and two sources of contact current in 36 homes in Pittsfield, MA. The first source, V(P-W), is the voltage due to current in the grounding wire, which extends from the service panel neutral to the water service line. This voltage can cause contact current to flow upon simultaneous contact with a metallic part of the water system, such as the faucet, and the frame of an appliance, which is connected to the panel neutral through the equipment-grounding conductor. The second is V(W-E), the voltage between the water pipe and earth, attributable to ground currents in the water system and magnetic induction from nearby power lines. In homes with conductive water systems and drains, V(W-E) can produce a voltage between the faucet and drain, which may produce contact current into an individual contacting the faucet while immersed in a bathtub. V(P-W) was not strongly correlated to the magnetic field (both log transformed) (r = 0.28; P < 0.1). On the other hand, V(W-E) was correlated to the residential magnetic field (both log transformed) (r = 0.54; P < 0.001), with the highest voltages occurring in homes near high voltage transmission lines, most likely due to magnetic induction on the grounding system. This correlation, combined with both frequent exposure opportunity for bathing children and substantial dose to bone marrow resulting from contact, lead us to suggest that contact current due to V(W-E) could explain the association between high residential magnetic fields and childhood leukemia.

Sizing equipment grounding conductors based on thermal damage curves

In solidly grounded power systems, where separate equipment grounding conductors are used inside conduit or other raceways, sizing the equipment grounding conductor (EGC) per the minimum specified in NEC Article 250-122, Table 25D-122, can result in an inadequate ground-fault circuit design. Depending upon the magnitude of the ground-fault current and the specific rating or settings of the overcurrent protective device, an EGC can be damaged or completely destroyed before an upstream overcurrent device can clear the fault. Maximum thermal damage to an EGC often results from low-level ground faults, where currents fall below the short delay pickup setting for the protective circuit breaker. It should be recognized that Table 250-122 of the NEC serves only as a guide in determining the minimum size of an EGC. This is emphasized by the note added beneath the cable, which states "Equipment Grounding Conductors may need to be sized larger than specified in this cable in order to comply with Section 250-2(d)." Section 250-2(d), states than an effective grounding path shall "have the capacity to conduct safely any fault current likely to be imposed on it." Unfortunately, Table 250-122 is often used as the only basis for selecting an EGC. Here we present an example that illustrates how selecting an EGC based only on Table 250-122 can result in a ground-fault circuit design that may violate Section 250-2(d).

NEC grounding requirements for parallel circuits

This article specifically addresses the requirements of Table 250-95 of the National Electrical Code(R) (NEC) for proper sizing of the equipment grounding conductors in parallel circuits. However, it must be remembered that the grounding path must also comply with Section 250-51, in particular (3), which requires that the grounding path have sufficiently low impedance to limit the voltage to ground and to facilitate the operation of the circuit protective devices. The note to Table 250-95 emphasizes the point that the equipment grounding conductors may need to be sized larger than specified in this table in order to comply with Section 250-51. The recommendations presented herein are based on a literal interpretation by the author of the NEC as written and may not necessarily agree with the Code Making Panel's intent.

NEC ampacity tables, circuit sizing, and developing standardized tables

The basic design considerations and applicable codes and standards requirements necessary for proper circuit sizing are set forth, based on the 1990 National Electric Code (NEC). Consideration is given to load current, insulation temperature rating, equipment terminal requirements, ambient temperature, voltage drop, energy costs, equipment grounding conductor size, raceway effects, etc. Examples are given describing the typical but often incorrect method and several alternative, but correct methods. Finally, guidelines and examples are given on methods to streamline this process using computer-generated, standardized tables for feeders, motors, and transformers. These tables reduce design time and assure increased quality control in the design process. >

Compliance Guide: OSHA and National Electrical Code Requirements for Grounding and Ground-Fault Protection on Construction Sites

After more than three years of deliberations, including several public hearings, OSHA has issued standards covering ground-fault protection for personnel on construction sites. These standards became effective on February 22, 1977. The requirements in the new standards are in addition to, not in lieu of, any other requirements for system-grounding and equipment-grounding conductors on construction sites. The new standards apply to 120-V 15- and 20-A single-phase receptacle outlets that are not a part of the permanent wiring of the buildings or structures on construction sites. The standards also cover flexible cords sets and cord- and plug-connected equipment that are energized from the above receptacle outlets. The grounding and ground-fault protection requirements for these receptacle outlets, cords, and portable equipment are included in this paper.

Equipment Grounding for Reliable Ground-Fault Protection in Electrical Systems Below 600 V

Equipment grounding is one of the most important, but least understood, requirements for reliable ground-fault protection. This paper defines the basic objectives of equipment grounding and analyzes the role of equipment grounding conductors in providing ground-fault protection for electrical systems below 600 V.