Voltage DropVoltage Drop• loss of voltage as it travels along a wireloss of voltage as it travels along a wire• lights dim, motors overheatlights dim, motors overheat• larger wires have less voltage drop for a larger wires have less voltage drop for a

given amount of currentgiven amount of current• longer wire = greater problemlonger wire = greater problem• must increase wire size as distance increasesmust increase wire size as distance increases

VoltmeterVoltmeter•Voltmeters measure the electromotive

force or voltage of a power source.•There are DC voltmeters that measure

DC voltage and AC voltmeters that measure AC voltage.

•One kilovolt (kV) is 1,000 volts•One millivolt (mv) is 1/1000 (.001) of a

volt•One microvolt (V is 1/1,000,000

(.000001) of a volt.

Power (Watts)Power (Watts)• When amperes flow (coulombs per second) at a When amperes flow (coulombs per second) at a

certain pressure (EMF), this is known as power. certain pressure (EMF), this is known as power. Wattage can be calculated by using the formulaWattage can be calculated by using the formula

• Power is the time rate of doing work.Power is the time rate of doing work.

• Electrical power is measured in watts (W), and Electrical power is measured in watts (W), and in kilowatts (kW).in kilowatts (kW).

• When calculating horsepower, there are 746 W When calculating horsepower, there are 746 W in 1 HPin 1 HP

twP

viP

5 Copyright © ODL Jan 2005 Open University

Malaysia

The characteristic of an element is to oppose current flow. The characteristic of an element is to oppose current flow. The more resistance, the less current flow and vise versa.The more resistance, the less current flow and vise versa.Resistor is used to resist or limit the current and divide the Resistor is used to resist or limit the current and divide the voltage. In general, there are three types of resistor, namely voltage. In general, there are three types of resistor, namely fixed resistor, variable resistor and potentiometer. The fixed resistor, variable resistor and potentiometer. The resistance is indicated by the colour line of the resistor. resistance is indicated by the colour line of the resistor. Various type of resistor are shown belowVarious type of resistor are shown below

Resistance

• Electrical resistance is measured in ohms.• An ohm is the amount of resistance that allows 1

volt to push 1 amp through an electrical circuit.• The symbol for ohm is the Greek letter omega (ΩΩ).• The resistance in a conductor depends on:

• Material used.• Diameter of conductor.• Length of conductor.• Temperature of conductor.

ResistorsResistors

Used mainly to control current flow. Resistance is the property of the resistors

because they oppose current flow.Its unit is Ohm (ΩΩ) and its symbol R, R = 50

ohms, 5Kohms.

7

• Resistor is a passive element that absorbs Resistor is a passive element that absorbs power from the voltage source. The absorbed power from the voltage source. The absorbed power can be formulated with a relation from power can be formulated with a relation from the Ohm’s Law.the Ohm’s Law.

RV

RVVP

orRIIIRP

VIP

2

2))((

OhmmeterOhmmeter

Correct method for using an ohmmeter.

9

Ohm’s LawOhm’s Law• Ohms law is the relationship between the volt, the Ohms law is the relationship between the volt, the

ampere, and the resistance.ampere, and the resistance.• Ohm’s Law defines that voltage is proportional to the Ohm’s Law defines that voltage is proportional to the

current and vice versa. The circuit current is inversely current and vice versa. The circuit current is inversely proportional to the resistance R. Current and voltage have proportional to the resistance R. Current and voltage have a linear relationship with resistance remain constant.a linear relationship with resistance remain constant.

IRVR

I

IV

1

CableCable• A cable is a large fiber or metal rope,

used for hauling, lifting, or towing.• A cable is also a bare or insulated

conductor consisting of one or several strands used to transmit electric power from one place to other with max. efficiecy .

• Three principal components of a cable are

• Conductor• Insulation• Sheath for mechanical protection

ConductorConductor• Copper is the most commonly used material in cable. It has a Copper is the most commonly used material in cable. It has a

high electrical and thermal conductivity. It is cheaper as high electrical and thermal conductivity. It is cheaper as compared to other good conductors such as silver and has compared to other good conductors such as silver and has high resistance against corrosion and can be easily and high resistance against corrosion and can be easily and efficiently jointed.efficiently jointed.

• The conductors are either manufactured in solid state or The conductors are either manufactured in solid state or sranded.sranded.

• The current carrying capacity of a cable depends upon the The current carrying capacity of a cable depends upon the cross sectional area of the conductor and number of strands.cross sectional area of the conductor and number of strands.

• The standard formation of stranded conductor comprises of The standard formation of stranded conductor comprises of 3,7,19,37,61,and 127 wires.3,7,19,37,61,and 127 wires.

• A 3/.029” size of the cable means there are three onductors A 3/.029” size of the cable means there are three onductors and each has a diameter of .029 inches.and each has a diameter of .029 inches.

• Conductors are also manufactured in square,oval and flat Conductors are also manufactured in square,oval and flat shape as bus bars for distribution board.shape as bus bars for distribution board.

• Aluminium as conductor is used where there would no Aluminium as conductor is used where there would no chemical or corrosion agents. Aluminium is widly used due to chemical or corrosion agents. Aluminium is widly used due to less weight per unit volume, which is 30% that of copper.less weight per unit volume, which is 30% that of copper.

InsulationInsulation• The purpose of the insulation is to deliver power

with safety. There are two types of insulation generally used for wiring cables.

• V.R.I.(vulcanised rubber insulation)• P.V.C.(poly venyle chloride)

i)V.R.I. Insulation• Rubber is generally used as insulation for

cables. But pure rubber does not with stand the atmospheric condition and becomes sticky. A little quantity of sulpher is therefore added to make it soft and moisture proof. V.R.I. Cable is used where the temperature of conductor does not exceed 60 C but can be used upto 80 C for a short period of 2 hours. Copper has chemical effect on rubber but this effect is overcome by tinning the copper conductors.

• ii) P.V.C insulation.ii) P.V.C insulation. The most commenly used insulation for cable The most commenly used insulation for cable

is P.V.C. It is several time better than rubber is P.V.C. It is several time better than rubber insulation. The P.V.C. cable can be used upto 70 C insulation. The P.V.C. cable can be used upto 70 C for continuous operation and upto 130 C for a short for continuous operation and upto 130 C for a short period say upto four hours. It offer high resistance period say upto four hours. It offer high resistance to heat and cease to burn after isolating from the to heat and cease to burn after isolating from the fire source. Unlike rubber it has no chemical action fire source. Unlike rubber it has no chemical action with oil, grease acids and chemicals.with oil, grease acids and chemicals.

iii) Other insulating cablesiii) Other insulating cables• Polyethylene insulation.Polyethylene insulation.• Varnish cambric insulation or Varnish cambric insulation or Empire tapeEmpire tape..• Paper insulation.Paper insulation.

Types of CableTypes of Cable• Nonmetallic sheathed cable: copper or Nonmetallic sheathed cable: copper or

aluminum wire covered with paper, rubber, or aluminum wire covered with paper, rubber, or vinyl for insulationvinyl for insulation

• Armored cable: flexible metal sheath with Armored cable: flexible metal sheath with individual wires inside. Wires are insulatedindividual wires inside. Wires are insulated

• Conduit: tubing with individually insulated Conduit: tubing with individually insulated wireswires

Types of cableTypes of cable• Single core cable.Single core cable. One solid or several stranded One solid or several stranded conductors having an insulationconductors having an insulation•

• Multicore cableMulticore cable.. It is a cable with several single cores, It is a cable with several single cores, insulated from each other and then insulated from each other and then enclosed in a common sheating.enclosed in a common sheating.

• Coaxial cableCoaxial cable• It is a cable consisting of an inner It is a cable consisting of an inner conductor, surrounded by a tubular conductor, surrounded by a tubular insulating layer typically made frominsulating layer typically made from a flexible material, all of which is then a flexible material, all of which is then

surrounded by another conductive layer surrounded by another conductive layer (typically of fine woven wire for flexibility, or of (typically of fine woven wire for flexibility, or of a thin metallic foil), and then finally covered a thin metallic foil), and then finally covered again with a thin insulating layer on the outside. again with a thin insulating layer on the outside.

• Ribbon cableRibbon cable A ribbon cable (also known as multi-wire A ribbon cable (also known as multi-wire planar cable) is a cable with many conducting planar cable) is a cable with many conducting wires running parallel to each other on the wires running parallel to each other on the

same flat planesame flat plane

An optical fiber cable is a cable containing one or more optical fibre. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable is to be deployed.

• Optical fiber cable

Wiring systemWiring system• 1. 1. Batten wiring systemBatten wiring system.. In this type of wiring the single core, twin core or In this type of wiring the single core, twin core or

three core cables can be used. The TRS (tough rubber three core cables can be used. The TRS (tough rubber sheated) cables are run on well seasoned, perfectly sheated) cables are run on well seasoned, perfectly straight and well varnished teak wood batten of straight and well varnished teak wood batten of thickness at least 13 mm. In this system the batten is thickness at least 13 mm. In this system the batten is fixed to the wall by means of screws and the wires are fixed to the wall by means of screws and the wires are held on the batten with the help of brass clips.held on the batten with the help of brass clips.

2. 2. Cleat wiring system.Cleat wiring system. This is the simple and cheap method of installation. This is the simple and cheap method of installation.

Porcelain, plastic or hard wood cleats are fixed on the Porcelain, plastic or hard wood cleats are fixed on the wall with the help of rawl plug at an interval of about 3 wall with the help of rawl plug at an interval of about 3 ft. Desired cables are strained tightly when erected. ft. Desired cables are strained tightly when erected. Such types of system is used for temporary purpose Such types of system is used for temporary purpose such as building under consruction and army camping.such as building under consruction and army camping.

• 3. Wood casing wiring system.3. Wood casing wiring system.• This is one of the oldest , reliable and safe system of This is one of the oldest , reliable and safe system of

wiring. This is expensive and requires much skill to install. wiring. This is expensive and requires much skill to install. In this system the cables are drawn in the grooves of In this system the cables are drawn in the grooves of wooden casing which is fixed with plug in the wall. The wooden casing which is fixed with plug in the wall. The casing is covered with wooden cap. This system is best casing is covered with wooden cap. This system is best suited for the dry situation. In this system the wirings are suited for the dry situation. In this system the wirings are easy to examine at any time and thus faults can be traced easy to examine at any time and thus faults can be traced easily. easily.

• 4. 4. Conduit wiring systemConduit wiring system..• In this type of wiring system, the insulated cable are In this type of wiring system, the insulated cable are

drawn into metallic or non-metallic pipes. Metal is a non drawn into metallic or non-metallic pipes. Metal is a non flammable material so the risk of fire is reduced. Nowadays flammable material so the risk of fire is reduced. Nowadays non-metallic conduit system is used for non-metallic conduit system is used for commercial,domestic and industrial installations. P.V.C. or commercial,domestic and industrial installations. P.V.C. or other similar plastic compound is used for the purpose.other similar plastic compound is used for the purpose.

House wiringHouse wiring• In many situations only a single phase is In many situations only a single phase is

enough to supply electricity to residential enough to supply electricity to residential consumers. However,when distributing three-consumers. However,when distributing three-phase electric power, a fourth or neutral cable phase electric power, a fourth or neutral cable is run to provide a complete circuit to each is run to provide a complete circuit to each house. Different houses in the street are placed house. Different houses in the street are placed on different phases of the supply so that the on different phases of the supply so that the load is balanced, or spread evenlyload is balanced, or spread evenly

• FusesFuses• A Fuse is like a light bulb.A Fuse is like a light bulb.• It will pass electricity untilIt will pass electricity until• it is over loaded, then the metalit is over loaded, then the metal• fuse link will burn open. fuse link will burn open. • A short circuit will cause an overloadA short circuit will cause an overload

Circuit Breaker /Fuses

ON

OFF

ON

OFF

Circuit BreakerA circuit breaker Is like a light switch.

If it is overloaded the switch willoverheat and click open. When

it cools down the switch can be reset.A short circuit will cause an overload

Good BlownOpen Good Tripped

Off

Not re-usable Re-usable

House Wiring

Determine if the circuit breaker is overloaded. Calculate total power Refrig. Toaster TV Microwave

Power = __400__ + _1200__ + _300___ + _600__ = _2500__ Watts/hour

Amps = watts = _2500_ = __11.4__ amps

Watts = Volts * amps

Amps = Watts Volts

Refrig400 Watts

Toaster1200 Watts

TV300 Watts

Microwave600 Watts

1 m18 m

CircuitBreaker

orFuse Box

20 A20 A20 A20 A

220 VACMeterFour outlets

on one breaker.

Ground (Zero Volts)

Hot wire

volts 220

Electric circuit.An electrical circuit is a network that has a closed loop, giving a return path for the current. A simple electrical circuits consists of a source of electricity (a battery, etc.), a load (a light bulb, motor, etc.), and two wires to carry electricity between the battery and the load.

SeriesSeries and parallel and parallel cicuitscicuits

• Components of an electric circuit can be connected in Components of an electric circuit can be connected in series or in parallel. Components connected in series series or in parallel. Components connected in series are connected along a single path, so the same current are connected along a single path, so the same current flows through all of the components. Components flows through all of the components. Components connected in parallel are connected so the same connected in parallel are connected so the same voltage is applied to each component.voltage is applied to each component.

• •

• In a series circuit, the current through each of In a series circuit, the current through each of the components is the same, and the voltage the components is the same, and the voltage across the components is the sum of the voltages across the components is the sum of the voltages across all the components. In a parallel circuit, across all the components. In a parallel circuit, the resistors are arranged so that each forms a the resistors are arranged so that each forms a separate path for a part os the total current. Also separate path for a part os the total current. Also the voltage across each of the components is the voltage across each of the components is the same, and the total current is the sum of the the same, and the total current is the sum of the currents through all the components.currents through all the components.

• In a series circuit, every device must function for In a series circuit, every device must function for the circuit to be complete. One bulb burning out the circuit to be complete. One bulb burning out in a series circuit kills the circuit. In parallel in a series circuit kills the circuit. In parallel circuits, each light has its own circuit, so all but circuits, each light has its own circuit, so all but one light could be burned out, and the last one one light could be burned out, and the last one will still function.will still function.

• Series circuits were formerly used for lighting in Series circuits were formerly used for lighting in electric multiple unit trains. electric multiple unit trains.

Series circuitSeries circuit• Resistors in SeriesResistors in Series

• RRTT = R = R11 + R + R22 + R + R33 + . . . + . . .• Total current.Total current.

• I=V/RI=V/RTT • Voltage drop in each resistor.Voltage drop in each resistor.

• VVd d in Rin R11= I.R= I.R11• VVd d inin RR22= I.R= I.R22

Current ramains the sameCurrent ramains the same

Parallel circuitParallel circuit• Resistors in ParallelResistors in Parallel

• 1/R1/RTT = 1/R = 1/R11 + 1/R + 1/R22 + 1/R + 1/R33 + . . + . . or or RRTT = R = R1.1. R R22 . R . R33 .../ R .../ R11 + R + R22 + R + R33 + . . . + . . .Total resistance must always be less than the Total resistance must always be less than the

valuevalueof any resistor in the circuitof any resistor in the circuit

• Total current.Total current.• IItt= I= I11 + I + I22 and I and I11= V/R= V/R11 and I and I22 = V/R = V/R22 • If the resistance and total Current are only known If the resistance and total Current are only known

then the branch current can be calculated by the then the branch current can be calculated by the formulae.formulae.

• II11 = I = It . t . RR22//RR11++RR22 • II22 = I = It . t . RR11//RR11++RR22

Voltage across all branches or paths of the Voltage across all branches or paths of the circuit is the samecircuit is the same

QuestionsQuestions• Find the voltage drop across each resistor Find the voltage drop across each resistor

and the total resistance of the circuit. Also and the total resistance of the circuit. Also the equivalent circuitthe equivalent circuit

Parallel circuitParallel circuit• Find.Find.

• An equivalent circuit .An equivalent circuit .• Totalcurrent of the circuitTotalcurrent of the circuit• Find branch currentFind branch current..

Series - parallel circuitSeries - parallel circuit• Find the voltage drop across each resistor Find the voltage drop across each resistor

and the total resistance of the circuit. Also and the total resistance of the circuit. Also the current flowing in the circuit.the current flowing in the circuit.

One way switchOne way switchHot Wire Neutral

wire

Single-Pole Switch

Light

Hot Wire Neutral wire

Two lights controlled by one switch

Double switchDouble switch Hot Wire Neutral

wireSwitch 1 Switch 2

CommonTravelers

Electrical SafetyElectrical Safety• Shock and Fire• Never disconnect any safety device• Don’t touch electrical items with wet hands or feet• Don’t remove ground plug prong• Discontinue use of extension cord that feels warm• Don’t put extension cords under carpet.• Blown fuse or breaker, determine cause• Don’t replace fuse with larger fuse• Don’t leave heat producing appliances unattended• Heaters & lamps away from combustibles• Don’t remove back of TV (30,000v when off)• Keep appliances dry. Use insulated tools wherever possible.• Don’t use damaged switches, outlets, fixtures, extension cords• Never use damaged portable leads. • If in doubt consider all wires live.• See that there is sufficient light around machinery, passage, stairs

etc.