Electrical Installation Design Guide: Calculations for Electricians and Designers (2nd Edition)Full description
Electrical Installation Design Guide: Calculations for Electricians and Designers (2nd Edition)
Electrical Installation and Maintenance NC II CG
Earthing and Electrical Grounding Installation | A Complete Guide What is Grounding or Earthing?
To connect the metallic (conductive) Parts of an Electric appliance or installations to the earth (ground) is called Earthing or Grounding In other !ords" to connect the metallic parts of electric machiner# and devices to the earth plate or earth electrode (!hich is $uried in the moisture earth) through a thic% conductor !ire (!hich has ver# lo! resistance resistance)) for safet# purpose is %no!n as Earthing or grounding To earth or earthing rather" means to connect the part of electrical apparatus such as metallic covering of metals" earth terminal of soc%et ca$les" sta# !ires that do not carr# current to the earth Earthing can $e said as the connection of the neutral point of a po!er suppl# s#stem to the earth so as to avoid or minimi&e danger during discharge of electrical energ#
Good to know
Di ffer encebet weenEar t hi ng,Gr oundi ngandBondi ng. 'et me clear the confusion among earhing" grounding and $onding Earthing and Grounding is the same terms used for earthing Grounding is the commonly word used for earthing in the North American standards li%e IEEE, NEC, ANSI and UL etc !hile" Earthing is used in European" Common !ealth countries and Britain standards like IS and IEC etc
The !ord Bonding used for ointing t!o !ires (as !ell as conductors" pipes or appliances together onding is %no!n as connecting the metallic parts of different machines !hich is not considered to $e carr#ing electric current during normal operation of the machines to $ring them at the same level of electric potential
NeedofEar t hi ngorGr oundi ng.WhyEar t hi ngi sI mpor t ant ? The primar# purpose of earthing is to avoid or minimi&e the danger of electrocution" fire due to earth lea%age of current through undesired path and to ensure that the potential of a current carr#ing conductor does not rise !ith respect to the earth than its designed insulation When the metallic part of electrical appliances (parts that can conduct or allo! passage of electric current) comes in contact !ith a live !ire" ma#$e due to failure of installations or failure in ca$le insulation" the metal $ecome charged and static charge accumulates on it I! a person touches such a charged metal " the result is a severe shoc% To avoid such instances" the po!er suppl# s#stems and parts of appliances have to $e earthed so as to transfer the charge directl# to the earth Below are the basic needs of Earthing. •
To protect human lives as !ell as provide safet# to electrical devices and appliances from lea%age current
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To %eep voltage as constant in the health# phase (If fault occurs on an# one phase)
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To Protect Electric s#stem and $uildings form lighting
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To serve as a return conductor in electric traction s#stem and communication
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To avoid the ris% of fire in electrical installation s#stems
Di ffer entT er msus edi nEl e ct r i c alEa r t hi ng •
Earth" The proper connection $et!een electrical installation s#stems via conductor to the $uried plate in the earth is %no!n as Earth
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Earthed" When an electrical device" appliance or !iring s#stem connected to the earth through earth electrode" it is %no!n as earthed device or simple *Earthed+
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Solidly Earthed" When an electric device" appliance or electrical installation is connected to the earth electrode !ithout a fuse" circuit $rea%er or resistance,Impedance" It is called *solidl# earthed+
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Earth Electrode" When a conductor (or conductive plate) $uried in the earth for electrical earthing s#stem It is %no!n to $e Earth Electrode Earth electrodes are in different shapes li%e" conductive plate" conductive rod" metal !ater pipe or an# other conductor !ith lo! resistance
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Earthing Lead- The conductor !ire or conductive strip connected $et!een Earth electrode and Electrical installation s#stem and devices in called Earthing lead
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Earth Continuity Conductor" The conductor !ire" !hich is connected among different electrical devices and appliances li%e" distri$ution $oard" different plugs and appliances etc in other !ords" the !ire $et!een earthing lead and electrical device or appliance is called earth continuit# conductor It ma# $e in the shape of metal pipe (full# or partial)" or ca$le metallic sheath or fle.i$le !ire
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Su# $ain Earthing Conductor - A !ire connected $et!een s!itch $oard and distri$ution $oard ie that conductor is related to su$ main circuits
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Earth %esistance" This is the total resistance $et!een earth electrode and earth in / (0hms) Earth resistance is the alge$raic sum of the resistances of earth continuit# conductor" earthing lead" earth electrode and earth
POI NTSTO BEEARTHED Earthing is not done an#ho! According to IE rules and IEE (Institute of Electrical Engineers) regulations" •
Earth pin of 12pin lighting plug soc%ets and 32pin po!er plug should $e efficientl# and permanentl# earthed
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All metal casing or metallic coverings containing or protecting an# electric suppl# line or apparatus such as GI pipes and conduits enclosing 4I5 or P4C ca$les" iron clad s!itches" iron clad distri$ution fuse $oards etc should $e earthed (connected to earth)
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The frame of ever# generator" stationar# motors and metallic parts of all transformers used for controlling energ# should $e earthed $# t!o separate and #et distinct connections !ith the earth
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In a dc 12!ire s#stem" the middle conductors should $e earthed at the generating station
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6ta# !ires that are for overhead lines should $e connected to earth $# connecting at least one strand to the earth !ires
Component sofEar t hi ngSyst em A complete electrical earthing s#stem consists on the follo!ing $asic components •
Earth Continuity Conductor
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Earthing Lead
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Earth Electrode
Component s of Electrical Earthing System
Ea r t hCont i nui t yConduc t ororEa r t hWi r e That part of the earthing s#stem !hich interconnects the overall metallic parts of electrical installation eg conduit" ducts" $o.es" metallic shells of the s!itches" distri$ution $oards"6!itches" fuses" 5egulating and controlling devices" metallic parts of electrical machines such as" motors" generators" transformers and the metallic frame!or% !here electrical devices and components are installed is %no!n as earth !ire or earth continuit# conductor as sho!n in the a$ove fig
The resistance of the earth continuit# conductor is ver# lo! According to IEEE rules" resistance $et!een consumer earth terminal and earth Continuit# conductor (at the end) should not $e increased than 7/ In simple !ords" resistance o! earth wire should #e less than &' 6i&e of the Earth Continuit# Conductor or Earth Wire depends on the ca#le si(e used in the wiring circuit
Si z eofEa r t hCont i nui t yConduc t or The cross sectional area of the Earth Continuity Conductor should not $e less than the half of the cross sectional area of the thic%est !ire used in the electrical wiring installation Generall#" the si&e of the $are copper !ire used as earth continuit# conductor is 16WG ut %eep in mind that" don8t use less than 736WG as earth !ire Copper strip is also can $e used as earth continuit# conductor instead of $are copper !ire $ut don8t go for it until manufacture recommend it
Ea r t hi ngLe adorEa r t hi ngJ oi nt The conductor !ire connected $et!een earth continuit# conductor and earth electrode or earth plate is called earthing oint or *Earthing lead+ The point !here earth continuit# conductor and earth electrode meet is %no!n as *connecting point+ as sho!n in the a$ove fig Earthing lead is the final part of the earthing s#stem !hich is connected to the earth electrode (!hich is underground) through earth connecting point There should $e minimum oints in earthing lead as !ell as lo!er in si&e and straight in the direction Generall#" copper !ire can $e used as earthing lead $ut" copper strip is also used for high installation and it can handle the high fault current $ecause of !ider area than the copper !ire A hard dra!n $are copper !ire is also used as an earthing lead In this method" all earth conductors connected to a common (one or more) connecting points and then" earthing lead is used to connect earth electrode (earth plat) to the connecting point
To increase the safet# factor of installation" t!o copper !ires are used as earthing lead to connect the device metallic $od# to the earth electrode or earth plate Ie if !e use t!o earth electrodes or earth plats" there !ould $e four earthing leads It should not $e considered that the t!o earth leads are used as parallel paths to flo! the fault currents $ut $oth paths should !or% properl# to carr# the fault current $ecause it is important for $etter safet#
Si z eoft heEa r t hi ngLe ad
The si&e or area of earthing lead should not $e less than the half of the thic%est !ire used in the installation The largest si&e for earthing lead is 16WG and the minimum si&e should not $e less than 96WG If 1:,;91 !ire is used or the load current is <;;A from the suppl# voltage" then it is recommended to use copper strip instead of dou$le earthing lead The earth lead connection methods is sho!n in the a$ove fig =ote- We !ill post additional article a$out Earth Plate si&e !ith simple calculations> 6ta# tune
Ear t hi ngEl e ct r odeorEar t hPl at e A metallic electrode or plate !hich is $uried in the earth (underground) and it is the last part of the electrical earthing s#stem In simple !ords" the final underground metallic (plate) part of the earthing s#stem !hich is connected !ith earthing lead is called earth plate or earth electrode A metallic plate" pipe or rode can $e used as an earth electrode !hich has ver# lo! resistance and carr# the fault current safel# to!ards ground (earth)
Si(e o! Earthing Electrode
oth copper and iron can $e used as earthing electrode The si&e of earth electrode (In case of copper) << (t!o foot !ide as !ell as in length) and 7,9 inch thic%ness Ie <8 . <8 . 7,9+ (@;;.@;;.1;; mm) In case of Iron <8 .<8 . + B @;;.@;;.@ mm It is recommended to $ur# the earth electrode in the moisture earth If it is not possi$le" then put !ater in the GI (Galvani&ed Iron) pipe to ma%e possi$le the moisture condition In the earthing s#stem" put the earth electrode in vertical position (underground) as sho!n in the a$ove fig Also" put a 7 foot (a$out 1;cm) layer o! powdered charcoal and lime mi)ture around the earth plate (don8t confuse !ith earth electrode and earth plate as $oth are the same thing) This action ma%es the possi$le increase in the si&e of the earth electrode !hich leads a $etter continuit# in the earth (earthing s#stem) and also helps to maintain the moisture condition around earth plate *S" We !ill post E.ample calculation a$out Earth Electrode 6i&ing> 6ta# tune Good to know"
on8t use co%e (after $urning coal in the furnace to emit all the gases and other components" the remaining 99D car$on is called co%e) or stone coal instead of charcoal (!ood coal) $ecause it causes to corrosion in the earth plate 6ince" the !ater level is different in the different areas therefore" the depth for earth electrode installation is also different in various areas ut" the depth for earth electrode installation should not $e less than 7;ft (1 meter) and should $elo! 7 foot (1;39mm) from the constant !ater level $otors" Generator " +rans!ormers etc should $e connected from to earth electrode t!o different places
Ear t hPl at eorEar t hEl ect r odeSi z ef orSmal li nst al l at i on
In small installation" use metallic rod (diameter B
Me t hodsofEa r t hi ng|T ype sofEa r t hi ng Earthing can $e done in man# !a#s The various methods emplo#ed in earthing (in house !iring or factor# and other connected electrical eHuipment and machines) are discussed as follo!s-
1) .Pl at eEar t hi ng: In plate earthing s#stem" a plate made up of either copper !ith dimensions @;cm . @;cm . 179mm (ie
plate
2) .Pi peEar t hi ng: A galvani&ed steel and a perforated pipe of approved length and diameter is placed verticall# in a !et soil in this %ind of s#stem of earthing It is the most common s#stem of earthing The si&e of pipe to use depends on the magnitude of current and the t#pe of soil The dimension of the pipe is usuall# 3;mm (7Fin) in diameter and <:Fm (ft) in length for ordinar# soil or greater for dr# and roc%# soil The moisture of the soil !ill determine the
length of the pipe to $e $uried $ut usuall# it should $e 3:Fm (7FFft)
3 ) .RodEa r t hi ng it is the same method as pipe earthing A copper rod of 7<Fmm (7,< inch) diameter or 7@mm (;@in) diameter of galvani&ed steel or hollo! section
Copper Rod Electrode Earthing System
4) .Ear t hi ngt hr ought heWat er man In this method of earthing" the !aterman (Galvani&ed GI) pipes are used for earthing purpose Ja%e sure to chec% the resistance of GI pipes and use earthing clamps to minimi&e the resistance for proper earthing connection
If stranded conductor is used as earth !ire" then clean the end of the strands of the !ire and ma%e sure it is in the straight and parallel position !hich is possi$le then to connect tightl# to the !aterman pipe
5) .St r i porWi r eEar t hi ng: In this method of earthing" strip electrodes of cross2section not less than
Gener almet hodofEar t hi ng/Pr operGr oundi ng I nst al l at i on( St epbySt ep) The usual method of earthing of electric eHuipments" devices and appliances are as follo!7
irst of all" dig a F.Fft (7F7Fm) pit a$out <;21;ft (@2 meters) in the ground (=ote that" depth and !idth depends on the nature and structure of the ground)
<
ur# an appropriate (usuall# <8 . <8 . 7,9+ (@;;.@;;.1;; mm) copper plate in that pit in vertical position
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Tight earth lead through nut $olts from t!o different places on earth plate
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Kse t!o earth leads !ith each earth plate (in case of t!o earth plates) and tight them
F
To protect the oints from corrosion" put grease around it
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Collect all the !ires in a metallic pipe from the earth electrode(s) Ja%e sure the pipe is 7ft (1;cm) a$ove the surface of the ground
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To maintain the moisture condition around the earth plate" put a 7ft (1;cm) la#er of po!dered charcoal (po!dered !ood coal) and lime mi.ture around the earth plate of around the earth plate
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Kse thim$le and nut $olts to connect tightl# !ires to the $ed plates of machines Each machine should $e earthed from t!o different places The minimum distance $et!een t!o earth electrodes should $e 7; ft (1m)
Earth continuit# conductor !hich is connected to the $od# and metallic parts of all installation should $e tightl# connected to earth lead
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At last ($ut not least)" test the overall earthing s#stem through earth tester If ever#thing is going a$out the planning" then fill the pit !ith soil The ma.imum allo!a$le resistance for earthing is 7/ If it is more than 7 ohm" then increase the si&e (not length) of earth lead and earth continuit# conductors Leep the e.ternal ends of the pipes open and put the !ater time to time to maintain the moisture condition around the earth electrode !hich is important for the $etter earthing s#stem
SIspeci ficat i onf orEar t hi ng 4arious specifications in respect to earthing as recommended $# Indian 6tandards are given $elo! Mere are fe! •
An earthing electrode should not $e situated (installed) close to the $uilding !hose installation s#stem is $eing earthed at least more than 7Fm a!a#
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The earth resistance should $e lo! enough to cause the flo! of current sufficient to operate the protective rela#s or $lo! fuses It8s value is not constant as it varies !ith !eather $ecause it depends on moisture ($ut should not $e less than 7 0hm)
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The earth !ire and earth electrode !ill $e the same material
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The earthing electrode should al!a#s $e placed in a vertical position inside the earth or pit so that it ma# $e in contact !ith all the different earth la#ers
Danger sOfNotEar t hi ngASuppl ySyst em As emphasi&ed on earlier" earthing is provided in order •
To avoid electric shoc%
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To avoid ris% of fire as a result of earth lea%age current through un!anted path and
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To ensure that no current carr#ing conductor rises to a potential !ith respect to general mass of earth than its designed insulation
Mo!ever" if e.cessive current is not earthed" appliances !ill $e damaged !ithout the help of fuse in place Nou should note that e.cessive current are earthed at their generating stations !hich is !h# earth !ires carries ver# little or no current at all It therefore implies that it is not necessar# to earth an# of the !ires (live" earth and neutral !ires) contained in a P4C Earthing the live !ire is catastrophic
I have seen a person %illed simpl# $ecause a live !ire got cut from overhead pole and fell to the ground !hile the ground !as !et E.cessive current is earthed at generating stations and if at all the earthing is not efficient due to fault" earth fault interrupters !ill $e there to help use help onl# !hen the po!er transmitted is a$ove the rating of our appliances" it $loc%s the current from reaching our appliances $# $lo!ing off and protecting our appliances in the process In our electrical appliances" if e.cessive currents are not earthed" !e !ould e.perience severe shoc% Earthing ta%es place in electrical appliances onl# !hen there is a pro$lem and it is to save us from danger If in an electronic installation" a metallic part of an electrical appliance comes in direct contact !ith a live !ire that results from ma#$e failure of installation or other!ise" the metal !ill $e charged and static charge !ill accumulate on it If #ou happen to touch the metallic part at that moment #ou !ill $e &apped ut if the metallic part of the appliance is earthed" the charge !ill $e transferred to earth instead of accumulating on the metallic part of the appliance Current don8t flo! through earth !ires in electrical appliances" it does so onl# !hen there is pro$lem and onl# to direct the un!anted current to earth in order to protect us from severe shoc% In addition" if a live !ire touches accidentall# (in a fault# s#stem) to the metallic part of a machine =o!" if a man touches that metallic part of the machine" then the current !ill flo! through their $od# to the ground" hence" he !ill get shoc%ed (electrocuted) !hich ma# lead to serious inuries even to death That8s !h# earthing is so important?
El e ct r i c alGr oundi ng&Ea r t hi ng…. .T obecont i nue d… Please su$scri$e $elo!" if #ou a$out EarthingGrounding such as•
!ant
to
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upcoming
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Calculate the si&e of Earth Continuit# Conductor" Earthing 'ead O Earth Electrodes for differnt electrical devices and eHuipment such motors" transformers" home !iring etc $# 6imple calculations
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Earthing Circuit and Earth ault Current
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Protection of Earthing 6#stem and Additional devices used in the Earthing , Grounding 6#stem
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Points To remem$er !hile Providing Grounding , Earthing
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Important Instruction for Proper earthing s#stem
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Electricit# rules a$out Earthing
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Mo! to Test Earth 5esistance $# Earth Tester
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Mo! to test Earth loop 5esistance $# Am2Jeter O 4oltmeter
