introduction to grounding system design

7/21/2019 Introduction to Grounding System Design

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3- Differences between Bonding and Grounding

• '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.



!- Grounding system definitions

hat is “Ground”#

'he ground is now simply the planet earth.

hat is “Effecti$e%y Grounded”#

'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.)



hat is “&o%id%y Grounded”#

(#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.



.ig +1* 3-wire/ sing%e-)hase systems

• 9or grounded 5+phase, 6+wire wiring systems +see fig,2& the neutral

point of the wye+connected transformer%s& or generator is usually the pointconnected to ground.

.ig +2* grounded 3-)hase/ !-wire wiring systems

• $n delta+connected transformer hooups +see fig,3 grounding of the



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.



hat is “Grounding 'onductor”#

• (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&.



.ig +!* Eui)ment ground

•'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.



hat is “Grounding E%ectrode”#

• 'he grounding electrode is any one of the building or structural

elements that is in actual physical contact with the earth, such as: see fig,

1. <etal nderground 8ater ?ipe.

2. <etal 9rame of the "uilding or @tructure.

3. #oncrete+Encased Electrode.

4. *round ing.

5. od and ?ipe Electrodes.

6. ?late Electrodes.

7. Other Bocal <etal nderground @ystems or @tructures %such as pipingsystems and underground tans&.



fig +* grounding e%ectrode Ty)es

hat is “Grounding E%ectrode 'onductor”# &ee fig,

• $t 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 andthe grounding electrode system for ungrounded systems.

• 'he conductor that runs from the bonded neutral bloc or busbar or

ground bus at service equipment, separately derived systems, or mainbuilding disconnects to the system grounding electrode is clearly and

specifically identified as the (grounding electrode conductor.)

hat is “Bonding um)er”# &ee fig,4

• 'his is the connection between noncurrent+carrying metalliccomponents of the electrical system that are provided to ensure continuity.

• 'hey may be bare, covered, or insulated conductors, or it may be a

mechanical device, such as screws often provided to connect a neutralterminal bar to a service enclosure.

• 'he primary function or purpose of a bonding umper is to provide a

low impedance electrically conductive connection between separateenclosures, conduits, raceways, structures, or equipment frames.

• $t must be properly si-ed to effectively carry any and all current

liely to be imposed on it.



fig +4* Bonding um)er

hat is Eui)ment Bonding um)er# &ee fig,C

• 'hese are bonding connections made between two portions of the

equipment grounding system.



.ig +7* 6ain Bonding um)er

• '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.



.ig +8* &ystem Bonding um)er

• '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.

introduction to grounding system design

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