Electricity Agri-Science I
When installing new appliances, equipment, tools, or any type of electrical convenience, it is important to know the electrical requirements for the item that you wish to connect.
It is equally important to know the availability and capacity of your electrical service.
Objectives • The student will be able to: • Make electrical calculations to determine circuit requirements and capacities using basic electrical formulas.
Enabling Objectives • Explain the relationship between Volts, Amps, and Watts. • Make calculations using the West Virginia Formula. • Determine the number of amperes a circuit will use. • Determine the size circuit interrupter needed for a circuit. • Determine the capacity of an existing circuit.
Amps Volts WattsThe following relationship exists between Amps, Volts and Watts. Amperes are a measure of the rate of flow of electricity in a conductor. Volts are a measure of electrical pressure. Watts are a measure of the amount of energy or work that can be done by amperes and volts.
Amps Volts Watts Thus, the following relationship exists. Work = Pressure x Flow Or Watts = Volts x Amperes
Amps Volts Watts This formula is commonly referred to as the West Virginia Formula W=VA When we know any two variables of the formula, we can calculate the other.
Formulas Watts = Volts x Amps Volts = Watts / Amps Amps = Watts / Volts
Calculating Amperage If we have a100 watt lamp plugged into a 120 volt receptacle, we can determine the rate of flow or the amperes for that circuit. Amps = 100 Watts / 120 Volts 100 / 120 =.833 Amps
Calculating Watts If a water heater operates at 20 amps on a 240 volt circuit, what is the wattage of the appliance? Watts = 240 Volts x 20 Amps 4800 Watts =240V x 20A Watts=4800
Calculating Volts If an electric motor operates at 2880 watts and 12 amps, what would be the voltage requirement for that motor? Volts = 2880 Watts / 12 Amps 2880 / 12 = 240 Volts
CircuitCalculations When installing branch circuits, it is important that we know the following information before we can begin. • The number of loads on the circuit. • The Watts of each load. • The Amperes required by each load . • The Voltage required by the load. • The distance from the service panel to the load.
CircuitCalculations Our first example will be to install a branch circuit for lights in a shop building. The load will be ten 120 watt light bulbs. The lights will operate on a 120 volt circuit. We can determine the amperage on this circuit by using the formula A= W / V. The amperage on this circuit will be the number of lights (10) x 120 Watts /120 Volts =10 Amps. Now we can correctly match our wire size and circuit breaker for the installation we desire.
CircuitCalculations Next we will install a individual branch circuit that will be used to operate an air compressor. The motor information plate reads that it operates on 120/240 volts and requires 15.4 / 12.1 amps. In this scenario, we do not need to make any calculations for voltage or amperage, and the watts will not need to be known to make this connection. However, the first amperage reading of 15.4 indicates the amperage that should be used when Calculating for a 120Volt circuit. 12.1 amps should be used for a 240 volt connection.
CircuitCalculations Next we will install a individual branch circuit for a hot tub. The hot tub operates two 3 HP pump motors which require 240 volts and 7.2 / 5.3 amps. The heater is a 240 volt, 5500 watt element. The air blower is a 240 volt, 2 amp motor. Now lets determine the size circuit interrupter we need. The 2 motors will account for 14.4 amps. The air blower will account for 2 amps. We will have to calculate the amperage for the heater. A = W/V A = 5500 / 240 or Amps = 22.9 Our total amperes is 14.4 + 2 + 22.9 = 39.3 Now we can determine the wire size and the circuit interrupter size needed.
Circuit Calculations Voltage Drop As electricity travels through conductors, it meets resistance and looses pressure or volts. The farther it has to travel, the greater the drop in voltage. This is called Voltage Drop.
Voltage Drop When we plan for a circuit, we must take into consideration the distance from the service panel to the load. By knowing the distance between the load and the service panel, and the amperage required by the load, and the circuit voltage required, we can refer to a chart that will to determine the size conductor needed for the circuit. This chart will take into account the type of conductor and give us the information needed.
Circuit Capacity Sometimes we need to know if an existing general purpose branch circuit can provide service to an added load. An example of this would be plugging in an air conditioner to an existing receptacle. If the circuit already provides service to other loads such as a television or a stereo, then the amperage for each of those would need to be determined. If the air conditioner operates on 120 volts and 2000 watts, lets determine the amps. A = W / V Amps = 2000 / 120 Amps = 16.7 This would be to much for a 15 amp circuit to run the air conditioner by itself. The circuit interrupter could be upgraded to a 20 amp interrupter if the wire size and receptacle ratings meet the requirements for a 20 amp circuit.
Review • Watts = work Amperes = rate of flow Volts = Pressure • Watts = Volts x Amperes or W = VA • W=VA is referred to as the West Virginia Formula • When planning a circuit we must know the number of loads, the amperes of each load, the voltage requirement for each load, the watts for each load and the distance from the service panel to the load. • Voltage drop is a loss of voltage due to resistance in the conductor.
Calculating Electric Power With the information we have discussed in this section, you should be able to plan and determine the needs for some common types of branch circuits. If you are ever unsure about your plan for a electrical connection, you should seek professional help before continuing.
Electrical Principles and Wiring Materials Original Power Point Created by Casey Osksa Modified by Georgia Agricultural Education Curriculum Office June 2002
Principles of Electricity • Electricity is a form of energy that can produce light, heat, magnetism, chemical changes • Resistance: tendency of a material to prevent electrical flow • Conductor: if electricity flows easily • Insulator: material that provides great resistance
Amps, Volts, Watts • Amperes: measure of the rate of flow of electricity in a conductor • Volts: measure of electrical pressure • Watts: measure of the amount of energy or work that can be done • Ohms: measure of electrical resistance to flow
Ohm’s Law • Ohm = R • Volts = E • Amps = I • Ohm’s Law: E = IR I=E/R R=E/I *Image from : http://home.neo.rr.com/mrwithdcc/Ohms.html
Electrical 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 • Use GFI in wet areas • Discontinue use of extension cord that feels warm • Don’t put extension cords under carpet
Electrical Safety • Install wiring according to NEC • 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) • Electric motors lubricated, free of grease etc.
Electrical Safety • Keep appliances dry • Don’t use damaged switches, outlets, fixtures, extension cords • Follow manufacturer’s instructions for installation and use of electrical equipment
Service Entrance • Power from from power company • Transformer: drops volts from 25,000 volts to 240 volts • Service drop: wires etc from transformer to house • Entrance head: weather-proof at house • Meter: $$$ • Service Entrance Panel (SEP): box with fuses or breakers
Electric Meter • Kilowatthours: how electricity is sold • Kilo = 1000 • Watthour = use of 1 watt for one hour • 100 watt light bulb for 1 hour - 100 watthours • Kilowatthour = 1000 watts for one hour
Branch Circuits • usually begin at SEP • branch out into a variety of places • only 1 motor or; • series of outlets or; • series of lights • use correct size wire and fuse or breaker
Types of Cable • Nonmetallic sheathed cable: copper or alluminum wire covered with paper, rubber, or vinyl for insulation • Armored cable: flexible metal sheath with individual wires inside. Wires are insulated • Conduit: tubing with individually insulated wires
Wire Type and Size • copper • No 14 (14 gauge) = 15 amp circuits • No 12 = 20 amps • No 10 = 30 amps • aluminum use one size larger • lower gauge number = larger wire • No 8 and larger use bundles of wires • current travels on outer surface of wire, so a bundle of smaller wires can carry more
Voltage Drop • loss of voltage as it travels along a wire • lights dim, motors overheat • larger wires have less voltage drop for a given amount of current • longer wire = greater problem • must increase wire size as distance increases
Wire Identification • Type of outer covering, individual wire covering, cable construction, number of wires • Wire type stamped on outer surface
Wire Types • Type T - dry locations • Type TW - dry or wet • THHN - dry, high temps • THW and THWN - wet, high temps • XHHW - high moisture & heat resistance • UF - direct burial in soil but not concrete
Wire Identification • Color coded: black, red, & blue = positive or hot wires which carry current to appliances • White = neutral wires carry current from appliance back to source • Green or Bare = ground all metal boxes and appliances
Wire Identification • Wire Size: 12-2 has two strands of No. 12 wire (black & white) • 12-2 w/g same, with one green or bare • 12-3 has three strands of No. 12 (black, red, white) • 12-3 w/g same, with green or bare
OBJECTIVES: • Performance Objective: Students will be able to identify and list the different types of wall switches and receptacles commonly use in electrical wiring for the home or farm stead
Enabling objectives: • Given the instruction in class, laboratory, and assignments- • Students will be able to list and identify the different types of wall switches, receptacles and their parts commonly used in wiring electrical circuits with a 70% accuracy:
Single pole Three-way switch Four-way switch Double switches Pilot light switch Switch/receptacles Timer switches Automatic switches Motion- sensor switches Programmable switches Time-delay switch Dimmer switch Switches to list and identify:
Normal receptacles 15 amps, 125 volts 15 amps,125 volts (grounded) 20 amps, 125 volts 15 amps, 250 volts High –voltage 30 amps 125/250 volts 50 amps, 125/250 volts Receptacles to list and identify:
Interest approach: • The uses of electricity are numerous and new developments are appearing nearly daily. • Electricity provides our homes, farms, businesses and industries with valuable resources that would otherwise be unavailable to us. • Science, medicine, transportation and even communications have been fortunate to make rapid technological advancements related to our understanding of electricity.
Interest approach: (Continued) • All phases of modern agriculture depend on the benefits of electricity • To better understand and benefit from the application of electricity • There are basic principles that one should become comfortable with.
Technical Content PowerPoint Presentations • Electrical Switches • Special Purpose switches • Electrical Receptacles • GFCI Receptacles
Evaluation: Receptacles and Switches
Identify the following switch • 1. A. three way B. single pole C. four way
Identify the following • 2. A. three way B. single pole C. four way
Identify the following • 3. A. three way B. single pole C. four way