Transcript Electrical Principles and Wiring Materials

Ag Eng I
Electricity Unit E
Electricity
Q. Who invented electricity?
A.
No one, it is based on laws of
physics
Benjamin Franklin is created with
the discovery of electricity. He
proved his theory by flying a kite in a
thunder storm.
Electricity
It took almost one hundred years from
the time of the discovery of electricity
until the first electrical machine or
invention was produced. Can you
guess what it was?
Light Bulb
Electricity
Where does our electricity come from
that we use at our home?
In eastern NC its Progress Energy.
They produce electricity for a profit
just like any other business.
Electricity
In rural communities, electric
membership co-ops were formed to
provide electricity to the places that
the for profit companies would not go.
In our school district that co-op is
Four County Electric.
Sources of Power
Power is produced by a generator. The
generator is driven by some type of
external power. The common
sources of external power are:
Fossil Fuels
Nuclear
Hydro-Electric
Solar
Sources of Power
In our area we have power produced
by
Coal burning plants in Wilmington
Nuclear plants at Shearon Harris and
South Port.
If you don’t see it on your
handout, then write it in. It
was added because it was
important.
Electrical Principles and
Wiring Materials
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: 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;
electrical power
 Watts = Volts x Amps
 W =VA
West Virginia formula
Ohm’s Law
 Ohm:
measure of electrical resistance
to flow
 Resistance = R
 Volts = E
 Amps = I
 Ohm’s Law: E = IR
I=E/R
R=E/I
Electrical Safety
Two hazards: 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
 Keep heaters & lamps away from
combustibles
 Don’t remove back of TV (30,000v when
off)
Electrical Safety
 Keep
appliances dry
 Don’t use damaged switches, outlets,
fixtures, extension cords
 Do not remove the long ground prong
from 120v three-prong plugs
 Follow manufacturer’s instructions for
installation and use of electrical
equipment
Service Entrance
 Power
comes from power company
 Transformer: drops volts from 25,000
volts to 240 volts
 Service drop: wires that carry
electricity from transformer to house
 Entrance head: weather-proof at
house
 Meter: measure in kw hrs = $$$
 Service Entrance Panel (SEP): box
with fuses or breakers
Electric Meter
 Kilowatthours:
 Kilo
how electricity is sold
= 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
Wire size is measured by gauges
 No 14 (14 gauge) = 15 amp circuits
 No 12 = 20 amps
 No 10 = 30 amps
 Copper is better conductor than aluminum
 aluminum uses one size larger than copper
 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
 Causes lights to 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, and
number of wires determines where
cable can be used
 Wire type stamped on outer surface
Wire Types
Type T - dry locations
 Type TW - dry or wet
 RHW – is rubber, heat + moisture resistant
 THHN - dry, high temps
 THW and THWN - wet, high temps
 XHHW - high moisture & heat resistance
 UF - direct burial in soil but not concrete
 SE/SEU – unarmored service entrance cabl
 ASE – armored service entrance cable
 USE – Underground service entrance

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
Definitions
Breaker – protects circuits
from overload of current by tripping to
break or open the circuit
 Fuse – protects circuits from overload
by melting a metal strip in the fuse
 Circuit
Def.
wire – current carrying conductor
under electrical pressure
 Neutral wire – current carrying
conductor not under pressure
 Ground wire – conducting wire that
transmits current to the earth to
minimize the danger of electrical
shock
 Hot
Computing Electrical Costs
 Watts
= Volts x Amps
 How many watts of electricity will a
7.5 amp motor use in 5 hrs on a 120
Volt circuit?
 W = 120 x 7.5
 = 900 x 5 hrs
 W = 4500
 How many kilowatts is this?
 4500/1000 = 4.5 kw
Calculating Volts
 Volts
equal watts divided by amps
V = W /A
 What volt circuit is needed for a 7.5
amp electric motor that uses 900
watts in one hour?
 V = 900 / 7.5
 V = 120
Calculating Amps
 Amps
= Watts / Volts
 What should the amp rating of an
electric motor be if it uses 1500 watts
of electricity in 1 hour in a 120v circuit?
 A = 1500 / 120
 A = 12.5
Cost of Electricty
$
= cost per kW x # of kw x hours use
 Note: kilowatt is 1000 watts
 If electricity costs $.12/kwh, how
much would it cost to use 2 kw per
hour for 10 hours?
 = $.12 x 2 kw x 10 hr
 = $2.40
Switches
 Single
pole- 2 terminals, one location
 Threeway – 3 terminals, two locations
 Fourway – four terminals and is used
in combination with three way
switches to control lights from three or
more locations
Proper Wire Sizing and
Protection of the Circuit
Fuse
A one time use device that protects the
circuit from overloading. If the circuit
is overloaded the fuse will “blow” (the
filament in the fuse will melt in two)
The size of fuse used will depend on
the size of wire that is being used in
the circuit
Circuit Breaker
Device that is used to keep the circuit
from becoming overloaded.
Overloaded circuits become hot and
can catch fire. Will “trip” if overloaded
The size of breaker depends on the
size wire that is being used on the
circuit.
Wire Size and Breaker Size
Wire Size
Size
14
12
10
8
6
Breaker
15
20
30
40
55
Wire sizes
AWG = American Wire Gauge – a standard
for designating the size of electrical wire
The larger the number, the smaller the
diameter of the wire.
The smaller number, the larger the diameter
of the wire
House Wiring
Most circuits in houses are either size
14 or 12.
Larger appliances such as dryers and
ranges use larger wire (10 or 8)
Wire Size Labeling
NEC state that all electrical
conductors have the following info
stamped on the wire
AWG Size
Voltage Rating
Insulation Type
Testing Agency
Number of Conductors
Example of Commmon Wires
 12/2
 12/2
wg
 12/3 wg
 14/2
 12/2 wg
 14/3 wg
Single pole switch and light
Receptacle is always hot
Two
threeway
switches
with light
at end of
run
Three way circuit with light at
beginning of run
Three
way
switch
with
light in
middle
Four way circuit with light at end
Always remember that
electricity can kill you. Be
certain all power is off before
attempting to work with any
electrical devices.
Safety first.