Electrical Ground System Definitions
Definitions of electrical ground, grounding, grounding system components & terms:
This article defines the terms used to describe the building electrical grounding system & its components, including grounding & grounded conductors, grounding electrode, bonding, ufer and related terms.
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Here are some elementary electrical ground, grounding, and ground wire definitions to help us get our terms straight when discussing electrical grounds, grounding, and ground bonds.
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Page top sketch and other electrical ground system sketches used in this article are used with permission and were provided courtesy of Carson Dunlop Associates, a Toronto home inspection education firm and inspection firm.
Ground: means the physical earth, the soil or ground. In some countries the term earth is used and is synonymous with ground. In the electrical code, ground means an electrically conducting connection, intentional or accidental, between an electrical circuit and the earth.
Grounded means that something has been electrically connected to the earth. Watch out: even among inspectors and electricians, people may use the term "ground" more loosely to refer to the equipment grounding conductor or other components. Also see Grounded Conductor (below).
Grounding electrode or ground electrode: a metal conductor, usually a solid copper-alloy rod of specified length, driven into the ground in order to provide a point for electrical connection between the building grounding system and ground or earth.
In the electrical code, the grounding electrode conductor is the conductor (a wire) used to connect the grounding rod(s) to the equipment grounding conductor (the ground bus and ground wires in the electrical panel) OR to the grounded conductor (the neutral bus and neutral wires) OR to connect both of these to the grounding electrode (which is usually the case in residential electrical systems).
Grounded Conductor (the neutral wire): by convention the grounded conductor or neutral wire is white or gray. In an electrical circuit the grounded conductor (white or neutral wire) normally carries electrical current between the un-grounded (hot) electrical wire and (back through the main electrical panel and grounding system) earth.
In the electrical code, a grounded conductor is one which has been intentionally grounded - connected to the earth.
The amount of current carried by the neutral wire is called the un-balanced load and depends on the characteristics of the electrical device being operated by the circuit. The neutral conductor is grounded in the main electrical panel. Be careful, inspectors and electricians, speaking loosely, may simply call this the "neutral wire".
Equipment Grounding Conductor (the ground wire): By convention the equipment grounding conductor (ground wire) is bare copper or carries green insulation. the individual wire in a (grounded) electrical circuit that is connected through the ground bus in the electrical panels and ultimately in the main electrical panel is connected to ground or earth.
In the U.S. National Electrical Code and most other model electrical codes, a grounding conductor is a conductor (metal wire, metal bar, etc) which is used to connect electrical equipment (like an electrical panel enclosure) or the grounded circuit (the neutral wires) of a wiring system to a grounding electrode (and thus to earth).
The ground wire in an electrical circuit does not normally carry any electrical current, but it remains available as an emergency path to allow current to flow to earth should an electrical fault such as a short circuit occur (a connection between a hot wire and some metal (conductive) material that could cause an electrical shock to someone), thus assuring that a fuse or circuit breaker in the main panel can sense the current flow and switch off the circuit.
Watch out: In an older two-wire armored cable (BX) electrical circuit, the metallic cable of the circuit may be serving as the only grounding conductor. This is not a safe installation: should the metallic cable sheath carry live current (say due to a fault or faulty electrial wiring) someone touching the BX cable can be shocked - an event witnessed by the author.
It helps to keep these terms straight if we remember that we use the ing form of the word grounding to mean that this conductor causes an electrical connection between earth and whatever the grounding conductor is connected to.
In the electrical code, a grounded conductor is one which has been intentionally grounded - connected to the earth. As reader WT Smith points out below, the grounded conductor is not necessarily synonymous with the neutral conductor.
Really? In a comment posted originally at DEFINITIONS of ELECTRICAL TERMS, Reader W. Thomas Smith noted by comment (28 Oct 2015) the following:
Please note that referring to "Grounded Conductor" and "Neutral conductor" as synonymous is deprecated by the NEC. There are many installations where the grounded conductor is NOT a neutral conductor, including the very common 3-phase 240/120 "high leg" delta installation, where the grounded conductor is definitely not a neutral. It is required that the "Grounded Conductor" be white or gray; the neutral conductor is not required to be this color unless it is grounded. I suggest changing the definition of "Grounded Conductor" to omit the present reference to the neutral conductor, and add a sentence or parenthetical comment (usually the neutral conductor on single-phase).
Bonding or Bonded: means that metallic parts are permanently joined so as to assure that they form a reliably continuous electrical path and that the parts are capable of conducting any electrical current that may be imposed on them.
A bonding jumper is a reliable electrical conductor used to connect metal parts together and a main bonding jumper is the connection between the grounded circuit conductor and the equipment grounding conductor at the electrical service (panel).
Ground bond: refers to a physical electrical connection between any metal component (like metal water pipes, metal gas piping, a metal electrical panel enclosure, or a neutral or ground bus in the main electrical panel) and the building electrical ground system.
In the main electrical panel the neutral wires are physically bonded to the ground wires (by a larger diameter wire or by a metal bar inside the panel) and the ground wire bus (a metal bar) is further connected to a grounding conductor that connects those components to the building ground system: one or more grounding electrodes and possibly a connection to an incoming metal water pipe that is buried outside. An electrician would say that the building's ground and neutral wires are bonded to earth
Bonding electrical components together makes certain that all of the joined items are at the same electrical potential (that is, that current will not flow from one to the other). Examples of electrical bonds in buildings include:
A UFER is an electrical ground connection to earth provided by a concrete encased grounding electrode. This approach to electrical grounding improves the ground connection to earth in areas where soils are so dry that otherwise grounding may be ineffective. UFER grounding has been included in the U.S. National Electrical Code (NEC) since 1968.
UFER electrical grounding was developed in 1942 by Herbert G. Ufer who worked as a consultant to the U.S. Army to improve electrical grounding for bomb storage vaults in Arizona where dry soils limited the efficacy of electrical grounding using a driven copper electrode hammered into the soil.
Below we include additional research citations on the efficacy of Ufer grounding for electrical systems & buildings where you'll see H.G. Ufer's seminal paper on Ufer ground in in bold font. Wikipedia's entry for Ufer ground points out that Ufer observed that concrete was more conductive than most types of soil, permitting grounding by concrete-encased electrodes.
In modern construction a UFER connection may refer to a continuously bonded steel re-bar (or other grounding electrode) used in construction of a concrete footing or slab that is in turn bonded to the electrical ground system for the building.
We presume that the increased area and conductivity of the larger area of concrete in contact with the soil combined with conductivity of the concrete itself is what gives an improved local electrical ground-to-earth connection for the building. - "Ufer ground", Wikipedia, retrieved 4/27/14, original source: http://en.wikipedia.org/wiki/Ufer_ground
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