1. Agricultural Systems Technology II
Electrical Wiring
Agricultural Systems Technology II

2. Objectives
Objective A: Explain the characteristics and measurement of electricity.
Objective B: Install basic electrical circuits.

3. What is electricity?
Electricity is the movement or flow of electrons in a conductor.
Resistance: tendency of a material to prevent electrical flow
Conductor: material that allows electricity to flow easily (Gold, Silver, Copper and Aluminum)
Insulator: material that provides great resistance to electrical flow (Rubber, Glass, Vinyl and Air)

4. How do I measure electricity?
Amperes: measure of the rate of flow of electricity (or current)
Volts: measure of electrical pressure
Watts: measure of the amount of power or work that can be done
Power equation: W=VA
Shows the relationship between watts, volts and amps.

5. Power Equation Watts = Volts x Amps
A light bulb that uses 5 amps on a 120 volt circuit uses how many watts of power?
W = 120v x 5a
W = 600 watts
V = W/A
A = W/V

6. Ohm’s Law Relationship between resistance, volts and amps
Ohm (the unit of resistance)= R
Volts (electromotive force)= E
Amps (inductance)= I
Ohm’s Law: E = IR
I=E/R
R=E/I

7. Current
Alternating current – electrons flow in both directions, changing rapidly
Used in buildings, houses
Direct current – electrons flow in one direction only
Used in vehicles, equipment powered by batteries

8. Electrical Safety Shock and Fire Never remove any safety device
Don’t touch electrical appliances or wiring with wet hands or feet
Don’t remove ground plug prong
Use GFI in wet areas
Stop using extension cord that feels warm or smells like burning rubber
Don’t run extension cords under carpet

9. Electrical Safety Always install wiring according to NEC
Tripped breaker or fuse determine cause
before resetting
Don’t replace fuse with larger fuse
Don’t leave heat producing appliances unattended or use near combustible material
Ground all metal cases and cabinets of electrical appliances

10. Electrical Safety
Don’t use cracked or damaged switches, outlets, fixtures or extension cords
Follow all manufacturer’s instructions for installation and use of all electrical equipment

11. What is a circuit? Electricity must flow in a circle called a circuit
Open circuit = circle is broken
Short circuit = no load, current increases and wires overheat/melt.
Fuses or circuit breakers prevent damage to wires if too much current, trip or blow

12. Service Entrance Power from from power company
Transformer: drops volts from 25,000 volts to 240 volts
Service drop: wires from transformer to house
Entrance head: weather-proof at house
Meter: Measures electricity use
Service Entrance Panel (SEP): main box with fuses or breakers

13. Electric Meter Energy: amount of power used over time
Kilowatt-hours: how electricity energy is measured and sold
Kilowatt = 1000 watts
Watt-hour = use of 1 watt for one hour
100 watt light bulb running for 1 hour =
100 watthours
Kilowatt-hour = 1000 watts for one hour

14. Branch Circuits usually begin at SEP
branch out into a variety of places
only 1 motor or
several outlets or
several lights
use correct size wire and fuse or breaker
Load determines wire size, wire size determines breaker size

15. Types of Cable
Nonmetallic sheathed cable: copper or aluminum wire covered with paper and vinyl for insulation
Armored cable: flexible metal sheath with individual wires inside, wires are insulated. Good against physical damage, bad in damp areas
Conduit: tubing with individually insulated wires, required for commercial jobs

16. Wire Type and Size Copper aluminum use one size larger
No 14 (14 gauge) = 15 amp circuits
No 12 = 20 amps
No 10 = 30 amps
aluminum use one size larger
lower gauge number = thicker 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

17. Wire Identification Wire type stamped on outer surface
Color coded: black or red is the hot wire that carries current to appliances
White = neutral wires carry current from appliance back to source
Green or Bare = ground all metal boxes and appliances for safety

18. Wire Identification
Wire Size: 12-2 has two strands of No. 12 wire (black & white)
12-2 w/g adds one green or bare
12-3 has three strands of No. 12 (black, red, white)
12-3 w/g adds one green or bare

19. Voltage Drop Loss of voltage as it travels along a wire
Caused by resistance
Lights dim, motors overheat, electronics damaged
Larger wires have less voltage drop for a given amount of current
Longer wire = greater resistance, more drop
Larger wire size must be used to overcome drop on a long wire

20. Objective B: Install Basic Circuits
Conductors of correct size for load
Boxes contain all electrical connections
Cable must be secured to box
Box must be secured to building

21. Basic Rules for Wiring Metal box must be grounded
Splice wires in boxes with wire nuts, no bare wires (except safety ground)
Only 1 wire to each terminal
Hot wire (black or red) attach to brass or black terminal
Neutral wire (white) attach to silver terminal
Ground wire attach to box or green terminal

22. Basic Rules for Wiring
If white wire used as hot must be marked with black paint or tape
All connections tight and secure to prevent spark or short
Receptacle – device for receiving plugs
Switch – device for interrupting flow of electricity
Always place switch on hot side of circuit (black or red wire)

23. Duplex receptacle circuit

24. Single switch light circuit

25. 3 way switch circuit (2 locations)

26. Testing circuits Use continuity or Ohmmeter
If circuit complete then beep or reading
If open then none
Turn off voltage in circuit

27. Testing Procedure Turn all switches to on Remove bulbs
Place probes on black and white wires at source(disconnected)
Correct if no reading

28. Testing Procedure Put light bulb in last fixture Repeat test
Should be a reading if bulb and circuit are good
Last test for grounded boxes
One probe on metal box
One probe on ground (safety wire at source)
Should be a reading

29. Source:
Agricultural Mechanics: Fundamentals and Applications by Ray V. Herren , Delmar Cengage Learning, Clifton Park, NY.