Electrical Principles and Electrical Principles and Wiring MaterialsWiring Materials

UNIT 33UNIT 33

Principles of ElectricityPrinciples of Electricity

Electricity is a form of energy that can Electricity is a form of energy that can produce light, heat, magnetism, chemical produce light, heat, magnetism, chemical changeschanges

Resistance: tendency of a material to Resistance: tendency of a material to prevent electrical flowprevent electrical flow

Conductor: if electricity flows easilyConductor: if electricity flows easily Insulator: material that provides great Insulator: material that provides great

resistanceresistance

CONDUCTORSCONDUCTORS SILVER-premium conductor (too SILVER-premium conductor (too

expensive)expensive) COPPER-very good conductorCOPPER-very good conductor ALUMINUM-good conductor(outside)ALUMINUM-good conductor(outside)

Amps, Volts, WattsAmps, Volts, Watts

Amperes: measure of the rate of flow of Amperes: measure of the rate of flow of electricity in a conductor. Watt/voltselectricity in a conductor. Watt/volts

Volts: measure of electrical pressure. Volts: measure of electrical pressure. Watt/amperesWatt/amperes

Watts: measure of the amount of energy or Watts: measure of the amount of energy or work that can be done. Volts x ampereswork that can be done. Volts x amperes

Ohms: measure of electrical resistance to Ohms: measure of electrical resistance to flowflow

Ohm LawOhm Law George Simon Ohm –made several George Simon Ohm –made several

discovers relating to electrical current.discovers relating to electrical current. Ohm law is the unit used to measure Ohm law is the unit used to measure

a material’s resistance to the flow of a material’s resistance to the flow of electrical current.electrical current.

Ohm’s Law --- FormulasOhm’s Law --- Formulas

Ohm = ROhm = R Volts = EVolts = E Amps = IAmps = I Ohm’s Law: E = IROhm’s Law: E = IR

I=E/R I=E/R

R=E/IR=E/I

MeasurementsMeasurements Voltage, amperage, and resistance can Voltage, amperage, and resistance can

be measured by various types of be measured by various types of meters.meters. Voltmeter – measures voltageVoltmeter – measures voltage Ammeter – measures amperageAmmeter – measures amperage Ohmmeter – measures resistanceOhmmeter – measures resistance

Electrical SafetyElectrical Safety Shock and FireShock and Fire Never disconnect any safety deviceNever disconnect any safety device Don’t touch electrical items with wet hands Don’t touch electrical items with wet hands

or feetor feet Don’t remove ground plug prongDon’t remove ground plug prong Use GFI in wet areasUse GFI in wet areas Discontinue use of extension cord that feels Discontinue use of extension cord that feels

warmwarm Don’t put extension cords under carpetDon’t put extension cords under carpet

Electrical SafetyElectrical Safety Install wiring according to NECInstall wiring according to NEC Blown fuse or breaker, determine causeBlown fuse or breaker, determine cause Don’t replace fuse with larger fuseDon’t replace fuse with larger fuse Don’t leave heat producing appliances Don’t leave heat producing appliances

unattendedunattended Heaters & lamps away from combustiblesHeaters & lamps away from combustibles Don’t remove back of TV (30,000v when off)Don’t remove back of TV (30,000v when off) Electric motors lubricated, free of grease etc.Electric motors lubricated, free of grease etc.

Electrical SafetyElectrical Safety

Keep appliances dryKeep appliances dry Don’t use damaged switches, outlets, Don’t use damaged switches, outlets,

fixtures, extension cordsfixtures, extension cords Follow manufacturer’s instructions Follow manufacturer’s instructions

(RTDM) for installation and use of (RTDM) for installation and use of electrical equipmentelectrical equipment

Power Generation & Distribution Power Generation & Distribution systemssystems

Power Plant to Step-up station(13,800 – Power Plant to Step-up station(13,800 – 22,000 volts)22,000 volts)

Step-up station thru transmission lines Step-up station thru transmission lines (69,000 – 750,000 volts) to a Step-down (69,000 – 750,000 volts) to a Step-down station.station.

Step-down station reduces to 7200-Step-down station reduces to 7200-14,000 volts to home transformer.14,000 volts to home transformer.

Service EntranceService Entrance Transformer: drops volts from 72,00-Transformer: drops volts from 72,00-

14,000 volts to 240 volts (three wires)14,000 volts to 240 volts (three wires) Service drop: wires etc from transformer to Service drop: wires etc from transformer to

househouse Entrance head: weather-proof at houseEntrance head: weather-proof at house Meter: $$$Meter: $$$ Service Entrance Panel (SEP): box with Service Entrance Panel (SEP): box with

fuses or breakersfuses or breakers

Electric MeterElectric Meter

Kilowatthours: how electricity is soldKilowatthours: how electricity is sold Kilo = 1000Kilo = 1000 Watthour = use of 1 watt for one hourWatthour = use of 1 watt for one hour

100 watt light bulb for 1 hour - 100 100 watt light bulb for 1 hour - 100 watthourswatthours

Kilowatthour = 1000 watts for one hourKilowatthour = 1000 watts for one hour

TermsTerms Alternating current (AC)Alternating current (AC) – Electrical – Electrical

current that alternates or changes current that alternates or changes direction several times per second. direction several times per second. Current moves on the direction the Current moves on the direction the voltage forces it.voltage forces it.

TermsTerms Direct Current (DC)Direct Current (DC) – Electrical current – Electrical current

flowing in one direction.flowing in one direction.

TransformerTransformer – a device used to increase or – a device used to increase or decrease voltage.decrease voltage.

CycleCycle – The flow of electricity in one direction, – The flow of electricity in one direction, the reverse flow of electricity in the other the reverse flow of electricity in the other direction, and the start of flow in the other direction, and the start of flow in the other direction.direction.

TermsTerms Single PhaseSingle Phase – most common. One – most common. One

transformer is used between the transformer is used between the distribution line and the meter. Has distribution line and the meter. Has three wires, two “hot” and one neutral. three wires, two “hot” and one neutral. Provides service for 120 volt and 240 Provides service for 120 volt and 240 volt systems.volt systems.

TermsTerms Three PhaseThree Phase – designed especially for – designed especially for

large electrical loads. More expensive large electrical loads. More expensive due to three wires and three due to three wires and three transformers. Advantage is that the transformers. Advantage is that the load is divided among the three phases load is divided among the three phases and design for three-phase motors.and design for three-phase motors.

TermsTerms Short circuitShort circuit – direct connection – direct connection

between “hot” & neutral wires.between “hot” & neutral wires.

TermsTerms FuseFuse – a device used to protect circuits – a device used to protect circuits

from an overload of current. Must be from an overload of current. Must be replaced.replaced.

Circuit breakerCircuit breaker – protects circuits. Can – protects circuits. Can be manually reset for further use.be manually reset for further use.

Time-Delay fuseTime-Delay fuse – a fuse having the – a fuse having the ability to carry an overload of a short ability to carry an overload of a short period before melting the fuse link.period before melting the fuse link.

TermsTerms Underwriters’ Laboratory (U.L.)Underwriters’ Laboratory (U.L.) – a – a

national organization that tests all types national organization that tests all types of wiring materials and electrical of wiring materials and electrical devices to insure they meet minimum devices to insure they meet minimum standards for safety and quality.standards for safety and quality.

TermsTerms National Electrical Code (N.E.C.)National Electrical Code (N.E.C.)

regulates electrical wiring installations. regulates electrical wiring installations. Regulations are approved by the Regulations are approved by the National Board of Fire Underwriters,National Board of Fire Underwriters,

Branch CircuitsBranch Circuits

usually begin at SEPusually begin at SEP branch out into a variety of placesbranch out into a variety of places only 1 motor or;only 1 motor or; series of outlets or;series of outlets or; series of lightsseries of lights use correct size wire and fuse or use correct size wire and fuse or

breakerbreaker

Types of CableTypes of Cable

Nonmetallic sheathed cable: copper or Nonmetallic sheathed cable: copper or aluminum wire covered with paper, aluminum wire covered with paper, rubber, or vinyl for insulationrubber, or vinyl for insulation

Armored cable: flexible metal sheath Armored cable: flexible metal sheath with individual wires inside. Wires are with individual wires inside. Wires are insulatedinsulated

Conduit: tubing with individually Conduit: tubing with individually insulated wiresinsulated wires

Wire Type and SizeWire Type and Size coppercopper No 14 (14 gauge) = 15 amp circuitsNo 14 (14 gauge) = 15 amp circuits No 12 = 20 ampsNo 12 = 20 amps No 10 = 30 ampsNo 10 = 30 amps aluminum use one size largeraluminum use one size larger lower gauge number = larger wirelower gauge number = larger wire No 8 and larger use bundles of wiresNo 8 and larger use bundles of wires current travels on outer surface of wire, so a current travels on outer surface of wire, so a

bundle of smaller wires can carry morebundle of smaller wires can carry more

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 must increase wire size as distance

increasesincreases

Wire IdentificationWire Identification

Type of outer covering, individual wire Type of outer covering, individual wire covering, cable construction, number of covering, cable construction, number of wireswires

Wire type stamped on outer surfaceWire type stamped on outer surface

Wire TypesWire Types

Type T – use in dry locations onlyType T – use in dry locations only Type TW – can used in dry or wet conditionType TW – can used in dry or wet condition THHN – dry location with high tempsTHHN – dry location with high temps THW and THWN - wet, high tempsTHW and THWN - wet, high temps XHHW - high moisture & heat resistanceXHHW - high moisture & heat resistance UF - direct burial in soil but not concreteUF - direct burial in soil but not concrete

Wire IdentificationWire Identification

Color coded: black, red, & blue = Color coded: black, red, & blue = positive or hot wires which carry current positive or hot wires which carry current to appliancesto appliances

White = neutral wires carry current from White = neutral wires carry current from appliance back to sourceappliance back to source

Green or Bare = ground all metal boxes Green or Bare = ground all metal boxes and appliancesand appliances

Wire IdentificationWire Identification

Wire Size: 12-2 has two strands of No. Wire Size: 12-2 has two strands of No. 12 wire (black & white)12 wire (black & white)

12-2 w/g same, with one green or bare12-2 w/g same, with one green or bare 12-3 has three strands of No. 12 (black, 12-3 has three strands of No. 12 (black,

red, white)red, white) 12-3 w/g same, with green or bare12-3 w/g same, with green or bare

Electrical exercise Electrical exercise

Problems in electricityProblems in electricity