Chapter 03 - Conductors and Wiring Accessories

8/11/2019 Chapter 03 - Conductors and Wiring Accessories

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IntroductionIntroductionElectrical conductors are substance orElectrical conductors are substance or

materials used to convey or allow the flowmaterials used to convey or allow the flowof electric currentof electric currentSilver, copper, aluminum, etcSilver, copper, aluminum, etc

Electrical insulators are substance orElectrical insulators are substance ormaterials that resist the flow of electricmaterials that resist the flow of electric

currentcurrentRubber, porcelain, etcRubber, porcelain, etc


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WiresWires they arethey aresmaller conductors 8smaller conductors 8

mm (AWG No. 8) andmm (AWG No. 8) andbelowbelowCablesCables they are largerthey are largerthan wirethan wireCordCord is an insulatedis an insulated

stranded wirestranded wire


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Characteristics of Wire SizeCharacteristics of Wire SizeWire SizeWire Size

AWG AWGCurrentCurrentCarryingCarryingCapacityCapacity

2 to 3 wires inc2 to 3 wires inccable orcable orracewayraceway

(Amp)(Amp)

Area AreaCircularCircular

MillsMills

ResistanceResistance /1000 ft/1000 ft

CurrentCurrentCarryingCarryingCapacityCapacity Amp for Amp for

Single WireSingle Wire

1414 1515 4,1074,107 2.582.58 2020

1212 2020 6,5306,530 1.621.62 2525

1010 3030 10,38010,380 1.021.02 4040

88 4040 16,51016,510 0.6410.641 5555

66 5555 26,25026,250 0.4100.410 8080

44 7070 41,74041,740 0.2570.257 105105


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ClassificationsClassifications

Solid WireSolid Wire TheyTheyare single wireare single wireStrandedStranded TheyThey

are group ofare group ofsmaller wiressmaller wirestwisted to form atwisted to form a

metallic string.metallic string.


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ReceptaclesReceptacles

RacewayRaceway It is the channel or wiringIt is the channel or wiringaccessories so designed for holdingaccessories so designed for holdingwires, cables, orwires, cables, or busbarsbusbars that arethat areeither made of metal, plastic, or anyeither made of metal, plastic, or anyinsulating mediums. Conduit pipe isinsulating mediums. Conduit pipe isthe most common electrical racewaysthe most common electrical raceways

used in all types of construction.used in all types of construction.ConnectorsConnectors a metal sleeve usuallya metal sleeve usuallymade of copper that is slipped overmade of copper that is slipped overand secured to the butted ends ofand secured to the butted ends ofconductors in making a joint. It isconductors in making a joint. It issometimes called splicing sleeve.sometimes called splicing sleeve.Convenient Outlet or Attachment CapConvenient Outlet or Attachment Cap

A device that by insertion into a A device that by insertion into areceptacles.receptacles.


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Wall OutletWall Outlet same as CO for attachment onsame as CO for attachment on

wire coming from a lamps and otherwire coming from a lamps and otherappliances.appliances.Lighting outletLighting outlet outlet intended for directoutlet intended for direct

connection with a lamp holder, lightingconnection with a lamp holder, lightingfixtures, etc.fixtures, etc.Receptacle OutletReceptacle Outlet outlet where one or moreoutlet where one or more

receptacles are installed.receptacles are installed.Junction BoxJunction Box an extension of the box wiring.an extension of the box wiring.ReceptaclesReceptacles are contact device installed atare contact device installed atthe outlet for connection of a singlethe outlet for connection of a singleattachment plugattachment plugSwitchSwitch a device that open or closed thea device that open or closed thecircuits in an electric circuit.circuits in an electric circuit.


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Ampacity Ampacity of Electricalof Electrical

Conductor Conductor It is the ability of the wire or conductor to carryIt is the ability of the wire or conductor to carrycurrent without overheatingcurrent without overheatingConductor resistance to current flow generateConductor resistance to current flow generatenot only heat but also contribute to the voltagenot only heat but also contribute to the voltage

dropdropCurrent size and rating should have sufficientCurrent size and rating should have sufficientampacityampacity to carry load. They should haveto carry load. They should have

adequate mechanical strength and should notadequate mechanical strength and should notbe less than the rating of the branch circuit andbe less than the rating of the branch circuit andthe maximum load to be served.the maximum load to be served.


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Types of CableTypes of Cable

Armored Cable (AC) Armored Cable (AC) used for both in exposedused for both in exposedand concealed workand concealed workMetal Clad Cable (MC)Metal Clad Cable (MC) used for serviceused for servicefeeders, branch circuit, and indoor or outdoorfeeders, branch circuit, and indoor or outdoor

workworkMineral Insulated Cable (MI)Mineral Insulated Cable (MI) used for dry, wetused for dry, wetor continuously moist location as service feedersor continuously moist location as service feeders

or branch circuit.or branch circuit.NonNon --Metallic Sheath Cable (NM)Metallic Sheath Cable (NM) -- usedusedspecifically for one or two family dwelling notspecifically for one or two family dwelling not

exceeding 3 story buildingsexceeding 3 story buildings


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Shielded NonShielded Non --Metallic Sheath Cable (SNM)Metallic Sheath Cable (SNM) used for hazardous location or in cable tray or inused for hazardous location or in cable tray or inraceway.raceway.

Underground Feeder and Branch Circuit CableUnderground Feeder and Branch Circuit Cable(UF)(UF) used for underground connectionsused for underground connectionsincluding direct burial in the ground or feeder orincluding direct burial in the ground or feeder orbranch circuit.branch circuit.Service Entrance CableService Entrance Cable primarily used forprimarily used for

service wire.service wire.


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Power and Control Tray Cable (TC)Power and Control Tray Cable (TC) usedused

for installation in cable trays, raceways, orfor installation in cable trays, raceways, orwhere it is supported by messenger wire.where it is supported by messenger wire.Flat Cable Assembly (FC)Flat Cable Assembly (FC) for fieldfor field

installation in metal surface or raceways.installation in metal surface or raceways.Flat Conductor Cable (FCC)Flat Conductor Cable (FCC) used forused forgeneral purposes such as appliancegeneral purposes such as appliance

branch circuit, and for individual branchbranch circuit, and for individual branchcircuits especially in hard smoothcircuits especially in hard smoothcontinuous floor surface.continuous floor surface.

Medium Voltage Cable (MV)Medium Voltage Cable (MV) use foruse forpower system up to 3,000 volts.power system up to 3,000 volts.


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Circular MillCircular Mill

Mil is equal to 1/1000 of an inch that is used toMil is equal to 1/1000 of an inch that is used tomeasure the diameter of round wire.measure the diameter of round wire.1 circular mil =1 circular mil = /4 square mill = 0.7854 square/4 square mill = 0.7854 squaremilmil

Area, circular mil = D Area, circular mil = D22

To find the circular mill area of any circle, just knowthe diameter in mils and then square this value.


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Factors Determining Wire SizeFactors Determining Wire Size

LengthLength

CrossCross --Sectional AreaSectional AreaMaterialsMaterials


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Resistance of WireResistance of Wire

R = 10.8 L / A (for copper)R = 10.8 L / A (for copper)

R = 17.0 L / A (for aluminum)R = 17.0 L / A (for aluminum)Where:Where:

RR -- wire resistance, ohmswire resistance, ohmsLL -- length of wire, ftlength of wire, ft A A -- area of wire, circular millsarea of wire, circular mills


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Voltage Drop and Power Loss inVoltage Drop and Power Loss in

WireWireVoltage Drop = Circuit Current xVoltage Drop = Circuit Current x

Resistance of Wire (I x R)Resistance of Wire (I x R)Power Loss = Circuit Current x VoltagePower Loss = Circuit Current x Voltage

Drop (I xDrop (I x VVdropdrop ))Power Loss = Component Resistance xPower Loss = Component Resistance xSquare of the Current (P = R x ISquare of the Current (P = R x I 22 ))


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Allowable Voltage Drop Allowable Voltage Drop

1%1% -- used for branch circuit wires andused for branch circuit wires and

loads involving constant voltageloads involving constant voltage2%2% -- adequate design for practically alladequate design for practically all

conditionsconditions3% average design figure3% average design figure

5% used only if the economy of wire cost5% used only if the economy of wire costdesireddesired


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Series CircuitSeries Circuit

Series ConnectionSeries Connection -- single path exist forsingle path exist for

current to flow; elements are arrange incurrent to flow; elements are arrange inseries one after the other; no branches;series one after the other; no branches;current is the same but the voltagecurrent is the same but the voltagediffer.differ.Voltage:Voltage: VVtt = V= V 11 + V+ V 22 + V+ V 33

Resistance:Resistance: RR tt = R= R 11 + R+ R 22 + R+ R 33 Current: ICurrent: I tt = I= I11 = I= I22 = I= I33


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Series Connection


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Sample ProblemCalculate the current flowing, the totalresistance and the voltage drop across eachresistor with the total applied voltage Et = 200v and the value of each resistor is R 1 = 24ohms, R 2 = 66 ohms, and R 3 = 44 ohms.

Et=200v

R1=24 R2=66 R3=44

It

Given:Et - 200 volt R 1 - 24 ohms

R 2 - 66 ohms R 3 - 44 ohms

Required: Rt, It, voltage drop


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Solution:

Rt = R 1+R 2 +R 3= 24 ohms + 66 ohms + 44 ohms

= 134 ohms

It = Et / Rt

= 200 v / 134= 1.49 amp

ER 1 = It R 1= 1.49 amp x 24 ohms = 35.6 voltER 2 = It R 2= 1.49 amp x 66 ohms = 108.34 volt

ER 3

= It R 3= 1.49 amp x44 ohms = 65.56 volt


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Parallel CircuitParallel Circuit

Parallel ConnectionParallel Connection multiple connectionmultiple connectionexist for current to flow; it is the standardexist for current to flow; it is the standardarrangement for house wiring connection;arrangement for house wiring connection;voltage is the same but current differs.voltage is the same but current differs.Voltage:Voltage: VVtt = V= V 11 = V= V 22 = V= V 33

Resistance: 1/RResistance: 1/R tt = 1/R= 1/R 11 + 1/R+ 1/R 22 + 1/R+ 1/R 33 Current: ICurrent: I tt = I= I11 + I+ I22 + I+ I33 ......


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Parallel Connection


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Sample ProblemThe total voltage Et of 200 volts is the sameacross all three resistive branches, R 1 is 40ohms, R 2 is 100 ohms, and R 3 is 200 ohms.Calculate the current flowing in each resistivebranches and also the total current.

Given:Et - 200 volt R 1 - 40 ohms

R 2 - 100 ohms R 3 - 200 ohms

Required: I1, I2, I3, It

Et=200v R1=40

It

R2=100 R3=200


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I1 = E / R1 = 200 v/40 ohms = 5 ampsI2 = E / R2 = 200 v/100 ohms= 2 amps

I3 = E / R3 = 200 v /200 ohms= 1 amps

It = I1 + I2 + I3

= 5 amps + 2 amps + 1 amp

= 8 amps


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Branch CircuitBranch Circuit

Electric CircuitElectric Circuit a complete patha complete path

traversed by an electric current.traversed by an electric current.Branch circuitBranch circuit it is the circuit conductorsit is the circuit conductors

between the final over current protectivebetween the final over current protectivedevice and the outlet. It is the wiringdevice and the outlet. It is the wiringinstalled between the circuit currentinstalled between the circuit current

protective device, i.e. fuse or circuitprotective device, i.e. fuse or circuitbreaker, and the outlets.breaker, and the outlets.


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Components of Branch CircuitComponents of Branch Circuit

Source of voltageSource of voltage

WiringWiringLoadLoad

Switch and FuseSwitch and Fuse


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Classifications of Branch circuitClassifications of Branch circuit

General Purpose Branch CircuitGeneral Purpose Branch Circuit suppliessupplies

outlets for lighting and small appliancesoutlets for lighting and small appliancesincluding convenience receptacles.including convenience receptacles.

Appliance Branch Circuit Appliance Branch Circuit Supplies outletSupplies outlet

intended for feeding appliances.intended for feeding appliances.Individual Appliance Branch CircuitIndividual Appliance Branch Circuit Intended toIntended tosupply a single specific item.supply a single specific item.


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Protection of Branch CircuitProtection of Branch Circuit

Branch circuit should be protected from overBranch circuit should be protected from overcurrent (any current in excess of the ratedcurrent (any current in excess of the ratedcapacity of the equipment or the rated capacitycapacity of the equipment or the rated capacityof the conductor) . It should always beof the conductor) . It should always beconnected at its hot line and to the voltageconnected at its hot line and to the voltagesource and its load end to the circuit wiring.source and its load end to the circuit wiring.Causes of over currentCauses of over current

Overload in the equipment or conductorsOverload in the equipment or conductorsShort circuit or ground faultShort circuit or ground fault


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FuseFuse an overall current protection devicean overall current protection device

with a circuit opening fusible element whichwith a circuit opening fusible element whichopen (break) when there is an over current inopen (break) when there is an over current inthe circuit.the circuit.

Circuit BreakerCircuit Breaker -- an over current protectivean over current protectivedevice designed to function as a switch. It isdevice designed to function as a switch. It isequipped with automatic tripping device toequipped with automatic tripping device toprotect the branch circuit from overload andprotect the branch circuit from overload andground fault.ground fault.

Trip or tripping refers to the cutting-off ordisconnection of the current supply.


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Factors to Consider inFactors to Consider in


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Factors to Consider inFactors to Consider in

Designing Branch CircuitDesigning Branch CircuitFlexibility of the circuitFlexibility of the circuit

Reliability and efficiency of serviceReliability and efficiency of serviceSafety of circuitrySafety of circuitry

Economy as to costEconomy as to costEnergy considerationEnergy consideration

Space allocationSpace allocation

Effect of Acquiring Low CostEffect of Acquiring Low Cost


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Effect of Acquiring Low CostEffect of Acquiring Low Cost

EquipmentEquipmentHigh energy costHigh energy cost

High Maintenance costHigh Maintenance costShorter lifeShorter life


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ReferencesReferences

Brown, R. 1956. Farm electrification. McGrawBrown, R. 1956. Farm electrification. McGraw --Hill Book Company. New York. 367pp.Hill Book Company. New York. 367pp.SubhashSubhash MethaMetha . Electrical Engineering.. Electrical Engineering.Synergy Books International. A division of SamSynergy Books International. A division of Sam

PublishingPublishing SdnSdn .. BhdBhd . 7. 7 JalanJalan Bangsar Bangsar UtamaUtama 3,3,OffOff JalanJalan Bangsar Bangsar , Kuala Lumpur Malaysia., Kuala Lumpur Malaysia.388pp.388pp.


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Chapter 03 - Conductors and Wiring Accessories