Introduction to Grounding System Desig n – Part One 1- Differences between Grounding and Earthing Te rms • “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 intent ional 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 nited !ingdom and part of the "ritish Electrical #ode and is employed in Europe or other countries that employs $nternational Electric #ommission %$E#& standards. • so, 'he term (earthing) in European or $E# countries is synonymous with the term (grounding) in North America. 2- Differences between Grounded and Grounding systems • *rounded system refers to a system where a conductor is grounded and is intended to or may carry current in the normal operation. 'he neutral on a wye system is a prime example of a grounded conductor . • 'he grounding conductor system is not intended to carry operational current in its design. 'his path is intended to carry unwanted and fault currents for protection.
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• 'he terms (bonding) and (grounding) are often employed
interchangeably as general terms in the electrical industry to imply or meanthat a specific piece of electrical equipment, structure, or enclosure issomehow referenced to earth.
• $n fact, (bonding) and (grounding) have completely different
meaning and employ different electrical installation methodologies.
• #omparison between bonding and grounding is given in the following
table:
sn Bonding Grounding
1 #onnection between non+liveconductive obects
#onnection between live or non+live conductive obects to earth
2 "onding is achieved by usingbonding conductors, metallic
raceways, connectors, couplings,metallic+sheathed cable withfittings, and other devicesapproved by the authority havingurisdiction as recogni-ed for thispurpose
*rounding is achieved by using arod or other suitable grounding
electrodes.
3 "onding for grounded systemprovides the safety during faultcurrent for persons
*rounding provides the safetyduring fault current forequipments without a need forbonding its enclosure
! "onding obects without
grounding one of them gives noprotection from stray currentsbut it protect from static charges
*rounding is independent on
bonding it gives equipmentprotection disregard it is bondedto its enclosure or not.
'he //01//21/33 National Electrical #ode defines effectively groundedas:
($ntentionally connected to earth through a ground connection orconnections of sufficiently low impedance and having sufficient current+carrying capacity to prevent the buildup of voltage that may result in undueha-ards to connected equipment of persons.4
hat is “Grounded”#
• 'he //0 NE# defines (*rounded) as: (#onnected to earth or to
some conducting body that serves in place of the earth.4
• 'he //2 NE# defines (*rounded) as: (#onnected to earth.)
• 'he /33 NE# defines (*rounded) as: (#onnected %connecting& to
ground or to a conductive body that extends the ground connection.)
(#onnected to ground %earth& without inserting any resistor or impedancedevice.4
hat is “Grounded 'onductor”#
• ( grounded conductor is the conductor of an electrical system that is
intentionally connected to earth via a grounding electrode conductor and agrounding electrode at the service of premises, at a transformer secondary,or at a generator or other source of electric power. $t is most commonly aneutral conductor of a single+phase, 5+wire system or 5+phase, 6+wiresystem but may be one of the phase legs7as in the case of a corner+grounded delta system.
• ( “grounded conductor” carries current during (normal) operations
of the power distribution system.
• %'he (grounded conductor) is commonly referred to as the neutralconductor.&
Grounded conductor in different system ty)es*
• $n 5+wire, single+phase systems +see fig,1 the midpoint of the
transformer 8inding, the point from which the system neutral is derived, isgrounded.
system can be effected by grounding one of the three phase legs, bygrounding a center+tap point on one of the transformer windings %as in the5+phase, 6+wire (red+leg) delta system&, or by using a special groundingtransformer which establishes a neutral point of a wye+connection which isgrounded.
.ig +3* de%ta-connected transformer hoo0u)s
The need for a grounded conductor*
• $t limits the voltage upon the circuit that might otherwise occur
through exposure to lightning or other voltages higher than that for whichthe circuit is designed.
• $t limits the maximum voltage to ground under normal operating
conditions.
• $t provides automatic opening procedure of the circuit if an
accidental or fault ground occurs on one of its ungrounded conductors.
• (A conductor used to connect equipment or the grounded circuit of a
wiring system to a grounding electrode or electrodes.4
• A (grounding conductor) is intended to only carry current during an(abnormal) operation of the power distribution system or a faultedcondition.
hat is the “Eui)ment Grounding 'onductor”# +see fig,!
• Equipment grounding is the intentional electrical interconnection of
all metal enclosures that contain electrical wires or equipment with thegrounding electrode conductor %all systems& and with the groundedconductor of the system %grounded systems only&.
•'he term equipment grounding conductor includes bare or insulated
conductors, metal raceways ;rigid metal conduit, intermediate metalconduit, electrical metallic tubing %E<'&=, and metal cable acets wherethe #ode permits such metal raceways and cable enclosures to be used forequipment grounding7which is a basic #ode+required concept.
Eui)ment grounding function*
• 8hen 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,) . 'his prevents theenclosures from remaining energi-ed, which would otherwise constitute ashoc or fire ha-ard.
• 'he connection between equipment ground and the grounding
electrode system in ungrounded services is a (bonding umper,) but not a(main bonding umper.)
hat is “&ystem Bonding um)er”# see fig,8
• 'he conductor, screw or strap that bonds the equipment bondingconductor %metal parts of a separately derived system& to one of the systemconductors or terminal.
• 'he system bonding umper provides the low+impedance fault+current
path to the source neutral for fault current.
• 'he primary function or purpose of the system bonding umper is to
provide for an applicable reference to earth for the system voltage at theorigins of the specific and separately derived system. 'he system bondingumper is a connection between the o terminal of a transformer, generator,or ?@ output terminals and earth. 'his umper is not normally si-ed tocarry ground fault current.