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Conduit 1
BENDINGCONDUIT/TUBINGUSINGHANDBENDERS
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Conduitisarugged,protectivetubethroughwhichwiresarepulled
Carefulplanningandpracticewillresultinaprofessionallookingelectrical
system
Aconduitwiringsystemisprobablythemostchallengingoftheelectrical
systemstoinstall
Althoughseveraltypesofconduitareusedinelectricalwork,onlythe
followingtypeswillbediscussedinthissubcourse:rigidsteel,electrical
metallictubing(EMT),rigidnonmetallic(polyvinyl chloride [PVC]),and
flexiblemetallicandnonmetallicconduit.
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RigidSteelConduitRigid
steel
conduit
is
a
heavy
duty
pipe
that
is
similar
in
appearancetometalwaterpipe.Itisthreadedatbothends.Rigidsteelconduitprovidesthebestprotectionfromphysicalabusebecauseofitsstrength.Article349inthe
NEC
covers
rigid
steel
conduit
(Figure
1
1,
page
1
2).
Thesizeofrigidsteelconduitistheinsidediametermeasurement.Rigidsteelconduitisavailableinsizesfrom
1/2inchto6inches.Thesesizeswillaccommodateanyjob.Abreakdownofthesizesofrigidsteelconduitininchesfollows:1/2,3/4,1,11/2,2,21/2,3,31/2,4,5,and6.
Afulllengthpieceorstickofrigidsteelconduitis10feetlong.Galvanizedsteelconduitisavailableforapplicationinwetareasorunderground.Galvanizingpreventstherustingof
conduit
from
moisture.
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EMTConduitEMT conduit is a light-gauge pipe often referred to as thin-wall
conduit (Figure 1-2). The wall thickness of EMT conduit is
about 40 percent less than that of rigid-steel conduit, and
because of the thickness of EMT conduit, it can be easily bent.Article 348 in the NEC covers EMT conduit.
EMT (thin-wall) conduit
EMT conduit is available in inside diameters ranging from 1/2
inch to 4 inches. Like rigid-steel conduit, EMT conduit comes
in 10-foot lengths. A breakdown of the sizes of EMT conduit
in inches follows: 1/2, 3/4, 1, 1 1/2, 2, 2 1/2, 3, 3 1/2, and 4.
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EMTConduitEMT conduit is a light-gauge pipe often referred to as thin-wall
conduit (Figure 1-2). The wall thickness of EMT conduit is
about 40 percent less than that of rigid-steel conduit, and
because of the thickness of EMT conduit, it can be easily bent.Article 348 in the NEC covers EMT conduit.
EMT (thin-wall) conduit
EMT conduit is available in inside diameters ranging from 1/2
inch to 4 inches. Like rigid-steel conduit, EMT conduit comes
in 10-foot lengths. A breakdown of the sizes of EMT conduit
in inches follows: 1/2, 3/4, 1, 1 1/2, 2, 2 1/2, 3, 3 1/2, and 4.
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RigidNonmetallic(PVC)ConduitPVC conduit is produced and used for below-ground (direct
burial or concrete encasement) installation. It provides highstrength, a low absorption rate, watertight joints, and low
installation costs. It is available in inside diameters ranging
from 1/2 inch to 5 inches. PVC conduit comes in lengths of upto 20 feet (Figure 1-3). Article 347 in the NEC covers PVC
conduit.
PVC conduit
A breakdown of the sizes of PVC conduit in inches follows: 1/2,
3/4, 1, 1 1/4, 1 1/2, 2, 2 1/2, 3, 3 1/2, 4, and 5.
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CuttingConduitRegardlessofthetypeofconduitbeinginstalled,
youwilloftenhavetocutittomakeitfit.All
conduitsshouldbecutata90 angle.Rigid
steelconduitcanbecutwitheitherahacksaw
orapipecutter.Althoughaviseisnot
absolutelynecessary,itmakescuttingwith
eithertoolmucheasier(Figure21).
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Typesoftools
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When cutting any conduit with a hacksaw, use a blade with 18 to 32 teeth per
inch
A blade with fewer teeth hangs up, binds, or even breaks
Put the blade in the hacksaw frame (with the teeth pointing forward) so that theteeth cut when you push the saw forward
Place the pipe in the vise so that there is ample room between the vise and the
cut
This lets you saw without hitting your hands on the vise and allows enough
room for threading purposes after the cut is made
Remember, let the saw work for you, do not force it
Use a steady forward cutting stroke with light to medium pressure.
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To use a pipe cutter, place the conduit in the vise as described above for cutting
with a hacksaw. Put the cutter over the conduit and adjust it until the
cutting wheel makes contact at the point of the cut
Tightenthecutterjustenoughtoscorethepipeonthefirstturn.Then,screwthe
handleinaboutonefourthofaturnforeachturnaroundtheconduituntilthecutis
complete.Cuttingoilcanbeusedtoeasethecuttingaction.Rigidsteelconduitiscut
thesameway.
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EMT and PVC conduit should be cut with a hacksaw because pipe cutters may
flatten the end of the pipe.
Pipe cutters also leave a ridge on the inside of the pipe that is very hard toremove. There are tubing cutters made specifically for cutting EMT or
PVC, but be sure you have the correct cutter for the job.
As stated before, when cutting conduit with a hacksaw or tubing cutter, using
the vise will make the job much easier.
The tubing cutter is used the same way as the pipe cutter.
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Flexiblemetallicandnonmetallicconduitshould
alsobecutwithahacksawata90 angleCuttinganytypeofconduitleavesasharpedge
or
burrs
on
the
inside
of
it
that
must
be
removedbyreaming
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To ream rigid-steel conduit, use the reamer.
A rat-tail file does a good job on any type of conduit.
Use pliers, such as needle-nose or side-cutting pliers, to ream
EMT that has been cut with a hacksaw.
The important thing is to remove any sharp edge or burrs inside
the conduit that might cut the insulation when the conductors
are pulled into it.
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ThreadingConduitOnce rigid-steel conduit is cut, it must be threaded for use with
threaded couplings, locknuts, and bushings.
To thread conduit, use a pipe-cutting die with a standard pipe
thread of 3/4-inch taper per foot.This die cuts a deeper thread on the end of the conduit and then
tapers the cut at the rear or shoulder of the thread. This is just
the opposite of a running thread on a bolt.
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The dies used for threading smaller sizes of conduit are usually
hand-driven
The handle may be solidly attached to the die, or the die assembly
may be a ratchet-type
When using larger sizes or installing large amounts of conduit
that require considerable threading, a motor-driven, pipe-
threading machine is recommend
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The most common rigid-steel conduit threader is a nonadjustable
ratchet and dies, which come in sizes to fit conduit from 1/2
inch to 2 inchesBefore threading the conduit, inspect the dies to see that they are
sharp and free from nicks and wear.
Next, insert the conduit into the vise, place the guide end of thepipe threader on the conduit, and push the threading dies
against the conduit with the heel of your hand
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With pressure against the threader, take three or four short, clockwise
strokes downward to start the threads.
Continue the threading with clockwise strokes, mixed with a reverse
stroke every now and then, until two or three threads extend beyond
the die.
To reverse the threader, pull the ratchet lock out and turn it a half turn.The reverse turns keep the threads and dies clean and free of bits of
metal.
Cutting oil applied during the threading helps the cutting process byreducing friction. To remove the threader, release the ratchet lock
and turn the die by hand counterclockwise. Removal of the die also
cleans the threads.
It is important that the right amount of threads be cut for the job. Inother words, a full thread must be cut so that the ends of the conduit
come together in the coupling
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Full threads are also necessary for the conduit to make a firm seat in the endthreads of the hub.
Cutting threads until two or three threads extend beyond the die usually givesyou a full thread.
However, if too many threads are cut, the conduit will fit too loosely in thecoupling or against the hub.
Power threaders come in the following two types: stationary threaders built for
use in the shop and portable threaders built for use in the field.
Both types are driven by electric motors that have adjustable chucks and diesfor use on different sizes of conduit.
Portable threaders normally handle conduit up to 2 inches.
Shop threaders may be built to handle conduit up to 6 inches.
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MethodsofBendingConduitWhenyouareinstallingconduit,youwillneedtomakebendstogooveror
aroundobstacles.
Thesebendsmustbemadewithoutreducingtheinsidediameterofthe
conduitatthebend.
Youwillmakemostbendsonthejobasapartoftheinstallationprocedure.
Thesearecalledfieldbends.
Factorymadebendsmaybeusedinsteadoffieldbends;however,they
increasethecostofthejobbecausetheyareanaddedcostandmay
requiremorecutting,threading,andbending.
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Sincemostofthebendingyoudowillbedonewithmanualbenders,the
bendingprocedurestaughtwillbemadewiththosetypesoftools.
Therearebasicallytwotypesofmanualbendersusedforbendingrigidsteel
conduitandEMT.
Theyaretherigidbender,calledthehickeys,andtheEMTbender.
TheEMTbenderisnormallymadeforEMT,butsomearemadetobeusedfor
bothEMTandrigidsteelconduit.
TheEMTbenderiscapableofmakingafull90 bendwithasinglemotion.
Conduit
sizes
up
to
1
inch
for
rigid
steel
and
1
1/4
inch
for
EMT
can
be
bentusingmanualbenders.
Largersizesareusuallybentwithpowerbenders
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TypesofBendsConduitinstallationsarenormallyreferredtoasrunsofconduit.
Arunofconduitistheconduit,fittings,straps,conductors,andbends
neededfromoneopeningtothenext(forexample,fromthepanelboard
tothefirstoutletboxorfromthefirstoutletboxtothesecondoutlet
box).
Inarunofconduit,therecannotbemorethantheequivalentoffour90
bends,foratotalof360.
Thepurposeofallowingonlysomanybendsinarunofconduitistohelpin
pullingconductorsintotheconduit.
Experiencehastaughtthatifmorethan360 ofbendsareused,itisvery
difficulttopullconductorsthroughthebends
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Theabilitytobendconduitandtubingisarequirementforallelectricians
Thereare fivemainbendsthatareusedbyelectricianstheseare:
stubupbacktoback
offset,boxoffset3
point
saddle
fourpointsaddleTheelectricianmustusecautionwhenbendingracewaystomakesurethatit
maintainsitsroundshapethroughoutthebentportionoftheraceway,in
ordertohelppreventjammingwhenpullingthewiresintoit
EMTisveryeasytobendbyhand
Itisathinwallgalvanizedmetaltubingthatisusedmostlyforinteriorconstruction
EMTbendersaresweepbendersoronesweep,onepiecebenders
Theyhaveacurvedtrackthattheracewayfollowsastheelectricianbendsthe
raceway
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TheracewayfitsintoacurvedtrackorslotintheEMTbenderwhichkeeps
theracewayfromspreadingoutasitisbent
Thiskeepstheracewayroundinthebendandalsokeepsitfromkinking
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RigidandIMCconduitarethehardestracewaystobendbecausetheyhaveamuchthickerandharderwallandrigidorIMCcanbebentbyhandusingahickey(orsegmentbender)
Ahickeybenderisusedtobendconduitinsmallbendswithshortsegments,forinstance,inordertobenda90 bendwiththistypeofbenderyouwouldbend9each10 bendswithshortgapsinbetweenthem
AnotherwaytobendrigidorIMCconduitbyhandistouseafullsweepbenderforrigidoruseanEMTbender
TouseanEMTbender,theelectricianwoulduseaEMTbenderforrigidorIMCandforrigidorIMC,hewouldusea1EMTbender
ThehickeybenderisonlyusedforRigidorIMC
ItwouldnormallykinkEMTtubing(exceptforverysmallbends)Largesizesofracewayscanbebentwithhydraulicbendersorwithmechanicalbenders,
suchasChicagobenders,thatincorporatearatchetingaction
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PVCconduitcanbebentwithheat.Heatbendersareusedonbigjobs,butfor
smalljobs,45 and90 elbowscanbepurchasedandgluedtogetherto
complete
the
run
if
no
heat
benders
are
available
Also,anEMTbendercanbeusedtobendsmalldegreebendsorkicksin
PVC.UseanEMTbendertobend30 kickinthePVCconduitbybendingit
to60 andthentheconduitwillspringbackto30
ThiswillonlyworkonorPVCandonlyforsmallbends,butitisfast
andprettyaccurate.
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TheEMTbenderhasdegreemarksonitformakingprecise10,221/2,30,
45 and60 bends
Thereisnota90 markonthebender.Thisbendismadebybendingtheracewayuntilitlooksliketheracewayisbentto90
Thiswillgeteasierwithexperience
TheEMTbenderalsohasseveralmarksthatareusedtolineupvarioustypes
ofbends.Thesearethearrow,thestarandtheteardrop
Theteardrop(ortherimmark)isusedforthecenterbendon3pointsaddles
Thestarisusedonbacktobackbends.Thearrowisusedforallotherbends