1. Electrical Principles and Wiring Materials
UNIT 33

2. 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

3. CONDUCTORS SILVER-premium conductor (too expensive)
COPPER-very good conductor
ALUMINUM-good conductor(outside)

4. Amps, Volts, Watts
Amperes: measure of the rate of flow of electricity in a conductor. Watt/volts
Volts: measure of electrical pressure. Watt/amperes
Watts: measure of the amount of energy or work that can be done. Volts x amperes
Ohms: measure of electrical resistance to flow

5. Ohm Law
George Simon Ohm –made several discovers relating to electrical current.
Ohm law is the unit used to measure a material’s resistance to the flow of electrical current.

6. Ohm’s Law --- Formulas Ohm = R Volts = E Amps = I Ohm’s Law: E = IR
I=E/R
R=E/I

7. Measurements
Voltage, amperage, and resistance can be measured by various types of meters.
Voltmeter – measures voltage
Ammeter – measures amperage
Ohmmeter – measures resistance

8. 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

9. 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.

10. Electrical Safety Keep appliances dry
Don’t use damaged switches, outlets, fixtures, extension cords
Follow manufacturer’s instructions (RTDM) for installation and use of electrical equipment

11. Power Generation & Distribution systems
Power Plant to Step-up station(13,800 – 22,000 volts)
Step-up station thru transmission lines (69,000 – 750,000 volts) to a Step-down station.
Step-down station reduces to ,000 volts to home transformer.

12. Service Entrance
Transformer: drops volts from 72,00-14,000 volts to 240 volts (three wires)
Service drop: wires etc from transformer to house
Entrance head: weather-proof at house
Meter: $$$
Service Entrance Panel (SEP): box with fuses or breakers

13. Electric Meter Kilowatthours: how electricity is sold Kilo = 1000
Watthour = use of 1 watt for one hour
100 watt light bulb for 1 hour watthours
Kilowatthour = 1000 watts for one hour

14. Terms
Alternating current (AC) – Electrical current that alternates or changes direction several times per second. Current moves on the direction the voltage forces it.

15. Terms
Direct Current (DC) – Electrical current flowing in one direction.
Transformer – a device used to increase or decrease voltage.
Cycle – The flow of electricity in one direction, the reverse flow of electricity in the other direction, and the start of flow in the other direction.

16. Terms
Single Phase – most common. One transformer is used between the distribution line and the meter. Has three wires, two “hot” and one neutral. Provides service for 120 volt and 240 volt systems.

17. Terms
Three Phase – designed especially for large electrical loads. More expensive due to three wires and three transformers. Advantage is that the load is divided among the three phases and design for three-phase motors.

18. Terms
Short circuit – direct connection between “hot” & neutral wires.

19. Terms
Fuse – a device used to protect circuits from an overload of current. Must be replaced.
Circuit breaker – protects circuits. Can be manually reset for further use.
Time-Delay fuse – a fuse having the ability to carry an overload of a short period before melting the fuse link.

20. Terms
Underwriters’ Laboratory (U.L.) – a national organization that tests all types of wiring materials and electrical devices to insure they meet minimum standards for safety and quality.

21. Terms
National Electrical Code (N.E.C.) regulates electrical wiring installations. Regulations are approved by the National Board of Fire Underwriters,

22. 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

23. Types of Cable
Nonmetallic sheathed cable: copper or aluminum 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

24. 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

25. 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

26. Wire Identification
Type of outer covering, individual wire covering, cable construction, number of wires
Wire type stamped on outer surface

27. Wire Types Type T – use in dry locations only
Type TW – can used in dry or wet condition
THHN – dry location with high temps
THW and THWN - wet, high temps
XHHW - high moisture & heat resistance
UF - direct burial in soil but not concrete

28. 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

29. 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

30. Electrical exercise
Problems in electricity