Where does electricity come from?

Introduction to Electricity

Objectives: Explain electricity and the kinds of electricity. Explain how electrical service is provided. Define the terminology used in electrical work. Identify and use the safety practices that should be observed in doing electrical work.

What is Electricity? The flow of electrons in a conductor. Form of energy that can produce light, heat, magnetism, and chemical changes Electrons= negative Protons= positive Neutrons= no charge

Conductor Substance that will allow for the flow of electricity Most common: copper, aluminum Best Conductor: Gold

Insulator Substance that does not allow for the flow of electricity Most common: Plastic, rubber, glass

Circuits The continuous path to and from an electrical source. Electrical devices are used as a part of the circuit. For example: Switches, lights, appliances Made of 2 wires and a ground: “Hot” conductor carries the electrical current from the source to the device. (usually black or red) “Neutral” conductor provides a return of the electrical current. (usually white)

Two kinds of electricity: Static Electricity Electrons do not move. Example: The shock received between two people who touch after walking on woolen carpet in cold weather. The reason a balloon sticks to the wall after you rub it on your head.

Example of Static Electricity Use 2 12 inch pieces of tape: Stick them to a flat surface. Quickly tear them away from the surface. How do the two pieces react when put closely together? Why?

Example of Static Electricity Use 2 6 inch pieces of tape: Stick together (sticky to non-sticky sides together). Exhale along the entire length. Quickly tear them apart. How do the two pieces react when put closely together? Why?

Two Kinds of Electricity Electrical Current Moving electrons. This is the type used in our work and daily lives. Can be in 2 forms: Direct Alternating

Direct current (DC) Flows in only one direction. Generated by battery-base electrical systems Used in internal combustion engines, flashlight batteries, welding.

Alternating current (AC) Reverses the direction and magnitude of electrons 60 times each second. AC is the type used in homes, factories, etc.

How do we get electricity in our homes and farms?

Electrical Service Begins with a power source. Usually a large generating plant that burns coal to produce electricity. Can also be wind, water, solar, etc. System of lines moves electricity to the user. (YOU!)

Electrical Service Provided to homes, farms, and businesses by three wires from a utility pole. Two of the wires are “HOT” each carrying 120 volts. The other wire is “neutral,” and provides the return path for electricity. Must have a complete circuit!!

Electrical Service Service entrance Wire are connected from pole to here. Where the electricity enters a building. A meter is used to measure the amount of electricity being used. Meter is always connected to grounding rod

Service Entrance Panel (SEP) Usually close to the meter. Used to distribute the power to individual circuits throughout the system. Two types: Breakers Fuses

Ohms, Volts, Watts, Amps Ohms: Measure of electrical resistance to flow. Volts: Measure of electrical pressure. Watts: Measure of the amount of energy or work that can be done (power). Amperes: Measure of the rate of flow of electricity in a conductor.

Principles of Electricity Resistance: Tendency of a material to prevent electrical flow. Voltage: Measurement of electricity in terms of pressure. Power: Result of hot current flowing for a period of time.

Match the following terms A. Ohms B. Volts C. Amps D. Watts Voltage is measured in _______ Resistance is measured in _____ Power is measured in _________ Amperes are measured in _______

Fuses Metal links melt when the current flow is too great. No moving parts. Must be REPLACED when it “blows”.

Circuit Breakers A heat-sensitive switch, which automatically trips when electricity demand is too great which causes the temperature in the conductor to get too hot. Operate on the principle that some metals expand more than others when heated equally. Does not need replaced when too much current passes through it.

Over-Current An over-current condition exists when the current flow in a circuit exceeds the amperage rating of the circuit’s conductors, loads or other devices. Excessive heat caused by an overcurrent condition may burn or damage a conductor’s insulation and cause a fire. The size of circuit breaker or fuse is determined by the size of wire used, which in turn is determined by the anticipated load of a circuit.

GFCI Ground Fault Circuit Interrupter Another type of breaker. Extremely sensitive to circuit imbalances in order to protect people who are using electrical devices near damp areas such as in bathrooms, kitchens, outside, etc. Prevent approximately 2/3rds of electrocutions that occur in the home.

National Electrical Code (NEC) Established guidelines for electrical wiring to ensure the safe use of electricity. They provide numerous rules for safe electrical installations. Local governments may also have codes that apply to the installation of wires, appliances, and other uses of electricity.

Measuring Electricity

Volts (Voltage) The pressure in a circuit that causes the electrons or current to flow. It is sometimes referred to as electromotive force (EMF). Measured in Volts, also known as “V” Measured with a voltmeter

Ampere (Current) Rate of electrical flow (volume of electricity flowing) Sometimes referred to as “amps” Also known as “I” AMPS KILL!

Watts (Power) Measure of electrical power. Electrical power is work being done by current (amperage) under pressure (voltage). Example – 100 watt light bulb 1500 watt blow dryer

Kilo-watt hour (KWH) Electricity is sold by the kilowatt hour (gasoline is sold by the gallon) Using 1000 (kilo) watts for one hour is a KWH 1 Kilowatt = 1000 watts

Horsepower Also a measure of power. Not used to measure electricity because it is too large. 746 watts = one horsepower

Match the following terms A. Ohms B. Volts C. Amps D. Watts Voltage is measured in _______ Resistance is measured in _____ Power is measured in _________ Amperes are measured in _______

Watts = Volts x Amps (Power Equation) P = V x I The amount of work that can be done in a circuit is equal to the voltage in the circuit times the amps Useful in determining how large a circuit should be, what size wire and circuit breaker/fuse is necessary.

P=V x I Analogy You can wash your car (do work) faster if you have a large hose with lots of pressure. A large hose will allow for greater flow of water (flow = amps) Pressure = voltage (force)

Using P=VI… V= 50 I= 1 How much power is in the circuit? P=100 watts V=120 V What is the current through the circuit?

Power Equation Assume that .83 amps of current flows through 120 volt circuit. How many watts of electrical power are being used? Using the formula: P = .83 amps x 120 volts = 99.6 (100 watts of power)

Power Equation Assume that there are 5, 100 watt light bulbs being operated on a 115 volt circuit. How many amps of current are flowing through the circuit? Answer: I = 500 watts = 4.35 amps of current 115 volts

Power Equation Assume that there is a 1200 watt coffee pot pulling 10 amps. What is the source of voltage? Answer: V = 1200 watts = 120 volts 10 amps

Power Equation To determine the wire size (and circuit breaker/fuse size), one needs to know what electrical devices or appliances might be operated on a given circuit. We know the voltage (120 V if normal household circuit) and you can find the wattage rating on the nameplate of each appliance or device being used. From this we can determine how many amps of current would flow through the circuit using the power equation…

Power Equation For example, assume that you plan to use a toaster rated at 1100 watts and a frying pan rated at 1200 watts on the same 120 volt circuit using copper wire. What size wire and what size circuit breaker should be used for that circuit?

Power Equation First, determine how many amps will flow through the circuit using the power equation. I = P ÷ V. I =2300 watts ÷ 120 volts =19.2 amps.

Power Equation National Electric Code table for allowable current-carrying capacities of insulated conductors. (copper wire) Gauge Amps 14 15 12 20 10 30 8 40 6 65

(don’t forget to show your work!) Thursday 1/8 Bellwork If an electric motor is pulling 5 amps from a 120 volt circuit, how much power is it using? _________ watts (don’t forget to show your work!)

Power Equation According to the table, you must use AWG #12 wire, which is rated for 20 amps. From this, you should also know that a 20 amp circuit breaker is necessary.

Ohm’s Law George Simon Ohm Ohm’s Law- relationship between electric current (Amps, or “I”), electromotive force (Volts, or “V”), and resistance (Ohms, or “R”)

Ohms (Resistance) The tendency of the wire to resist the flow of electrons or current through the wire. Resistance is measured in ohms. The relationship of ohms (R), volts (V), and amps (I) is V=I x R.

Resistance Electrical resistance is dependent upon size, length, and the material of the wire. Smaller wire = more resistance Longer wire = more resistance Silver, copper, and aluminum offer the least resistance.

Thursday (1/14/10) Bellwork Ohm’s Law V=IR Assume that there are 6 amps of current flowing through a 120 volt circuit. What is the resistance? Using the formula, R = 120 volts ÷ 6 amps = 20 ohms

Ohm’s Law V = Volts I = Amperes R = Resistance V = IR, or… The electromotive force is equal to amperes times resistance or Can also compute amperes and resistance I = V R = V R I

Using Ohm’s Law: V=IR I= 0.5 amps R= 200 Ω How much voltage is in the circuit? V= 120 V I= 1 amp How much resistance is in the circuit?

Ohm’s Law V=IR Assume that 10 A of current flows in circuit having a total resistance of 11 ohms. What is the source voltage? Using the formula: V= I x R, V= 10 A x 11 ohms. Thus, V = 110 volts.

Ohm’s Law V=IR Assume that you need to know how much current is flowing through a 115 volt circuit containing 25 ohms of resistance. What is the amperage of the circuit? Using the formula, I = 115 volts ÷ 25 ohms = 4.6 amps

How Much Will My Electric Bill Be? (1/11)

Electricity is priced and sold by the Kilowatt-hour. (kilo-1000) If you use 1000 watts of electricity for 1 hour, you use 1 kwh The price of a kwh of electricity is about 9 cents ($0.09)

How does it add up? How much does it cost to run ten 100 watt light bulbs for one hour? 10 x 100 = 1000 watts 1000 watts = 1 KWH 1 KWH x $0.09 = $0.09 (9 cents)

How much does it cost? Assume that you have three 300 watt bulbs on the outside of your house. You turn the lights on at 9:00 p.m. and turn them off the next morning at 7. How much does it cost to run the bulbs through the night? How much does it cost if you do this everyday for the entire year?

Answer How long did the bulbs run? (From 9 until 7 is 10 hours) How many total watts? 3 x 300 watts = 900 watts Watt-hours = 10 hrs x 900 watts = 9,000 watt-hours 9000 watt-hrs/1000 kilowatt = 9 KHW x $0.09 = $0.81 $0.81/day x 365 days = $295.65 per year

Try this one! A 5000 watt clothes dryer will dry a load of clothes in 1 hour. How much does it cost to dry the load of clothes? 5000 watts * 1 hr. = 5000 watthours 5000 watthours/1000 = 5 kilowatthours 5 kwh * .08 = $.40 (40 cents)

Answer 36 bulbs x 500 = 18000 watts Time = 5 hours 18000*5=90000 watthours 90000/1000 = 90 kwh 900 * $.08 = $7.20

Friday (1/12) Bellwork P=____________, measured in _________. I=____________, measured in _________. V=____________, measured in _________. R=____________, measured in _________.

Parallel Circuit A circuit that has more than one way that electricity can flow. Most common type of circuit

Series Circuit Has only one pathway for electricity to follow. If there are more than one device in the circuit, the electricity must flow through one device and continue on to the next device. Not normally used in houses. Christmas lights are sometimes wired in series. That is why if one bulb goes out the whole strand goes out

Calculating Electricity Cost A football field has 36 bulbs rated at 500 watts. The coach turns on the lights at 5:00 p.m. and turns them off after the game at 10:00 p.m. How much does it costs to run the lights during the game?

Wiring Simple Circuits

General Rule NEVER plug anything in until it has been checked!

Wire Color Black and Red are HOT wires. White is a NEUTRAL wire. Both carry current from source to the device that needs power. White is a NEUTRAL wire. Used to carry current back to the source. Never switch a neutral wire. Defeats purpose of switch!

Types of Wire HOT NEUTRAL GROUND

Switches Brass= HOT Silver= NEUTRAL Green= GROUND

Switch-Loop Circuits Used in three- and four-way switches. Require a white conductor to actually carry “hot” current. Used in three- and four-way switches. Common in rooms where more than one switch is used for a single light.

“Pig-tails” “Pig-tail” or “wire nut” wires together rather than attempting to attach multiple wires to a single screw. No bare wire should be exposed. Wire nuts should be enclosed in circuit box.

Attaching Wires Strip insulator. Curl wire. Loop around screw. Tighten screw.

Replacing Plugs on Extension Cords Pull cable through. Strip a small amount in insulator off. Attached wire to screws: Black to brass White to silver Ground to green

Diagramming Tips Draw the white, neutral conductor from the source to its final destination (device needing current, in our case the light) within the circuit, first. Switching should be done on the “hot” wire (not neutral.) The ground should have a connection to each box.