Introduction to Grounding System Design – Part One

1- Differences between Grounding and Earthing Terms “Grounding” is a term used rather exclusively in North American to indicate a direct or indirect connection to the planet Earth or to some conducting body that serves in place of the Earth.  Or, "Grounding": A conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the Earth, or to some conducting body of relatively large extent that serves in place of the Earth. “Earthing” is a term developed by the United Kingdom and part of the British Electrical Code and is employed in Europe or other countries that employs International Electric Commission (IEC) standards.  so, The term “earthing” in European or IEC countries is synonymous with the term “grounding” in North America.

2- Differences between Grounded and Grounding systems Grounded system refers to a system where a conductor is grounded and is intended to or may carry current in the normal operation. The neutral on a wye system is a prime example of a grounded conductor. The grounding conductor system is not intended to carry operational current in its design. This path is intended to carry unwanted and fault currents for protection.

3- Differences between Bonding and Grounding The terms “bonding” and “grounding” are often employed interchangeably as general terms in the electrical industry to imply or mean that a specific piece of electrical equipment, structure, or enclosure is somehow referenced to earth.  In fact, “bonding” and “grounding” have completely different meaning and employ different electrical installation methodologies. Comparison between bonding and grounding is given in the following table: s/n Bonding Grounding 1 Connection between non-live conductive objects Connection between live or non-live conductive objects to earth 2 Bonding is achieved by using bonding conductors, metallic raceways, connectors, couplings, metallic-sheathed cable with fittings, and other devices approved by the authority having jurisdiction as recognized for this purpose Grounding is achieved by using a rod or other suitable grounding electrodes. 3 Bonding for grounded system provides the safety during fault current for persons Grounding provides the safety during fault current for equipments without a need for bonding its enclosure 4 Bonding objects without grounding one of them gives no protection from stray currents but it protect from static charges Grounding is independent on bonding it gives equipment protection disregard it is bonded to its enclosure or not.

4- Grounding system definitions

What is “Ground”? The ground is now simply the planet earth.

What is “Effectively Grounded”? The 2005/2008/2011 National Electrical Code defines effectively grounded as:  “Intentionally connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current-carrying capacity to prevent the buildup of voltage that may result in undue hazards to connected equipment of persons."

What is “Grounded”? The 2005 NEC defines “Grounded” as: “Connected to earth or to some conducting body that serves in place of the earth." The 2008 NEC defines “Grounded” as: “Connected to earth.” The 2011 NEC defines “Grounded” as: “Connected (connecting) to ground or to a conductive body that extends the ground connection.”

What is “Solidly Grounded”? “Connected to ground (earth) without inserting any resistor or impedance device."

What is “Grounded Conductor”? A grounded conductor is the conductor of an electrical system that is intentionally connected to earth via a grounding electrode conductor and a grounding electrode at the service of premises, at a transformer secondary, or at a generator or other source of electric power. It is most commonly a neutral conductor of a single-phase, 3-wire system or 3-phase, 4-wire system but may be one of the phase legs—as in the case of a corner-grounded delta system.  A “grounded conductor” carries current during “normal” operations of the power distribution system. (The “grounded conductor” is commonly referred to as the neutral conductor.) Grounded conductor in different system types:  In 3-wire, single-phase systems (see fig.1) the midpoint of the transformer Winding, the point from which the system neutral is derived, is grounded.  Fig (1): 3-wire, single-phase systems For grounded 3-phase, 4-wire wiring systems (see fig.2) the neutral point of the wye-connected transformer(s) or generator is usually the point connected to ground.  Fig (2):  grounded 3-phase, 4-wire wiring systems In delta-connected transformer hookups (see fig.3) grounding of the system can be effected by grounding one of the three phase legs, by grounding a center-tap point on one of the transformer windings (as in the 3-phase, 4-wire “red-leg” delta system), or by using a special grounding transformer which establishes a neutral point of a wye-connection which is grounded.  Fig (3):  delta-connected transformer hookups The need for a grounded conductor:  It limits the voltage upon the circuit that might otherwise occur through exposure to lightning or other voltages higher than that for which the circuit is designed.  It limits the maximum voltage to ground under normal operating conditions.  It provides automatic opening procedure of the circuit if an accidental or fault ground occurs on one of its ungrounded conductors.

What is “Grounding Conductor”? “A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes."  A “grounding conductor” is intended to only carry current during an “abnormal” operation of the power distribution system or a faulted condition.

What is the “Equipment Grounding Conductor”? (see fig.4) Equipment grounding is the intentional electrical interconnection of all metal enclosures that contain electrical wires or equipment with the grounding electrode conductor (all systems) and with the grounded conductor of the system (grounded systems only).  Fig (4):  Equipment ground The term equipment grounding conductor includes bare or insulated conductors, metal raceways [rigid metal conduit, intermediate metal conduit, electrical metallic tubing (EMT)], and metal cable jackets where the Code permits such metal raceways and cable enclosures to be used for equipment grounding—which is a basic Code-required concept.  Equipment grounding function:  When the insulation failure occurs on a grounded system, equipment grounding serves to ensure adequate current flow to cause the affected circuit’s over-current protective device to “open,” . This prevents the enclosures from remaining energized, which would otherwise constitute a shock or fire hazard.

What is “Grounding Electrode”? The grounding electrode is any one of the building or structural elements that is in actual physical contact with the earth, such as: see fig.5 Metal Underground Water Pipe. Metal Frame of the Building or Structure. Concrete-Encased Electrode. Ground Ring. Rod and Pipe Electrodes. Plate Electrodes. Other Local Metal Underground Systems or Structures (such as piping systems and underground tanks). fig (5): grounding electrode Types

What is “Grounding Electrode Conductor”? See fig.5 It is the connection between either the grounded conductor of a grounded electrical system (typically the neutral) and the grounding electrode system, or the connection between the equipment ground bus and the grounding electrode system for ungrounded systems.  The conductor that runs from the bonded neutral block or busbar or ground bus at service equipment, separately derived systems, or main building disconnects to the system grounding electrode is clearly and specifically identified as the “grounding electrode conductor.”

What is “Bonding Jumper”? See fig.6 This is the connection between noncurrent-carrying metallic components of the electrical system that are provided to ensure continuity. They may be bare, covered, or insulated conductors, or it may be a mechanical device, such as screws often provided to connect a neutral terminal bar to a service enclosure.       The primary function or purpose of a bonding jumper is to provide a low impedance electrically conductive connection between separate enclosures, conduits, raceways, structures, or equipment frames.  It must be properly sized to effectively carry any and all current likely to be imposed on it. fig (6): Bonding Jumper

What is Equipment Bonding Jumper? See fig.7 These are bonding connections made between two portions of the equipment grounding system.  fig (7): Equipment Bonding Jumper    The purpose of the equipment bonding jumper is to provide the low-impedance fault-current path necessary to facilitate the operation of overcurrent protection devices in order to remove dangerous voltage potentials between conductive parts of building components and electrical systems

What is “Main Bonding Jumper (MBJ)”? see fig.8 A main bonding jumper provides the Code-required connection between the grounded system conductor and the equipment ground bus at the service equipment for a building or structure.  The MBJ must be adequately sized to effectively carry all phase-to-ground fault current likely to be imposed on it. Fig (8): Main Bonding Jumper The connection between equipment ground and the grounding electrode system in ungrounded services is a “bonding jumper,” but not a “main bonding jumper.”

What is “System Bonding Jumper”? see fig.9 The conductor, screw or strap that bonds the equipment bonding conductor (metal parts of a separately derived system) to one of the system conductors or terminal. Fig (9): System Bonding Jumper The system bonding jumper provides the low-impedance fault-current path to the source neutral for fault current.  The primary function or purpose of the system bonding jumper is to provide for an applicable reference to earth for the system voltage at the origins of the specific and separately derived system. The system bonding jumper is a connection between the Xo terminal of a transformer, generator, or UPS output terminals and earth.  This jumper is not normally sized to carry ground fault current.

In the next Article, I will continue explaining An Introduction to Grounding System Design. Please, keep following.

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