Transcript Electricity Unit Notes

ELECTRICAL PRINCIPLES
Electricity is the major power source of
stationary equipment
Uses:
Driving Machinery
Lighting
Heating
Cooling
Knowledge of electricity is essential for safe
use of electrical equipment
Electricity- a form of energy that can produce
light, heat magnetism and
chemical changes
Light- produced by heating a special metal
element or filament in a vacuum tube
called a “bulb”. Electricity flows through
certain gases causing them to glow
Insulator- provides great resistance to the flow
of electricity
Materials:
rubber-glass-vinyl-air
Amperes- measure of the rate of flow of
electricity in a conductor
Volts- measure of electrical pressure
Watts- measure of the amount of energy that
can be completed by amps and volts
Formulas:
Watts=volts x amps
Volts=watts x amps
Amps=watts x volts
Fluorescent lamp- glows as a result of electricity
flowing through a gas
Heat- is produced when electricity flows through
metals with some difficulty
Resistance- tendency of a material to prevent
electricity to flow
Conductor- metal permits electricity to flow
easily
Materials:
silver-aluminum-copper
•
•
•
used in outdoors
used in wiring for homes
heat develops in implements
Ohm’s Law: used to measure a material’s
resistance to the flow of
electrical current
E=volts
E
=
I
X
R
I=amps
R=resistance
Magnetism- force that attracts or repels iron
or steel
- permanent magnet
- when iron or steel holds its magnetism
2 ends or poles
- north
- south
Opposites attract/likes repel
Magnetic field- force between 2 objects
Electric Motors- principle of magnetism is the
basis upon which electric
motors operate
Reverses the Polarity: reversing the direction
of current flow
Electromagnet- unit is called
Commutator- reveres the current flow in an
electric motor
Armature- rotating magnet
magnetic forces around the armature are
called the “field”
Generators & Alternators- produce electricity
Generator- produces current (direct)
- flows one way
Alternator- produces current (alternating)
Turbine- high speed rotary engine driven by
water-steam-gas
Circuits- circle of electricity
- open circuit- broken
- closed circuit- together
Short Circuit- flow through the circle & back
to the source too rapidly
Grounding- connection between a piece of
equipment & the earth
- ground rod- steel or copper
- ground wire- bare
* channels stray electricity
Electricity Safety: 2 deadly hazards with
current
- shock
- fire
Shock- body’s reaction to a current
GFCI- Ground Fault Circuit Interrupter
-cuts off electricity if it leaves the pathway
Electrical Wiring: Systems have to be:
-safe
-convenient
-neat
-expandable -provide sufficient current
Service Entrance: Power company provides
-transformer
-service drop
-appropriate
wiring
Entrance Head- waterproof device used to
attach exterior wires to
interior wires
Transformer- converts high voltage to 240
volts-usable form for homes
- step up
- step down
Service Drop- assembly of electrical wiresconnectors & fasteners used to
transmit electricity from the
transformer to the entrance
head
Service Entrance Panel- box with fuses or
breakers where
electricity enters a
building
Meter- measurement of electricity in kilowatt
hours-Kilo means 1, 000
Watt Hour- use of 1 watt for 1 hour
Kilowatt Hour- use of 1, 000 watts for 1 hour
Reading a Meter: the last number passed by
each pointer is read
1st & 3rd dials turn counterclockwise
2nd & 4th dials turn clockwise
Branch Circuits- branch out to a variety of
places for many purposes
Fuse: plug or cartridge containing a strip of
metal that melts when more than a
specified amount of current passes
through
Circuit Breaker:
switch that trips & breaks the circuit when
more than specified amounts pass through it
- reset breaker after it trips
Types of Cables:
3 systems of wiring:
-Non-metallic sheathed
-Armored cable
-Conduit
Non-metallic Sheathed Cable:
-copper/aluminum
-waterproof
-approved for burial
Armored Cable:
-flexible metal sheath
-mechanical damage protection
Conduit:
Tubing consists of individual insulated wires
EMT-electrical metallic tube
Conduit can be:
-rigid
-bendable
-provide the most protection
Wire Type & Size:
Copper
Aluminum
Wire size designated by gauge: lower the
gauge larger the
wire
Strands- small wires placed together are called
“bundles”
- improves conductivity & flexibility
- electricity carried on outside of wire
Voltage Drop- refers to a loss of voltage as the
electricity travels along a wire
-larger the wire, less voltage drop
-longer the wire, more voltage drop
Wire ID: factors to determine wire
-outer covering
-number of wires
-individual wire covering
-cable construction
Wire type is stamped on outside
Type
Type
Type
Type
T- dry locations
TW- dry or wet locations
THHN- dry locations, high temperatures
THW & THWN- wet locations, high
temperatures
Type XHAW- high moisture & heat resistance
Type UF- buried in soil (not concrete)
NEC- National Electric Code
Hot Wires- colors (positive)
-black -red -blue
Neutral Wires- color
-white
Ground Wire- colors
-green -bare
Typical markings: 12-1, 12-2, 12-3 with
ground
INSTALLING BRANCH CIRCUITS
NEC- controls restrictions on wiring
Wiring Boxes:
-metal
-plastic
-hold work in place
-nail or screw to framing
-contains all electrical connections
-square/octagonal/rectangular
Wire Nuts- insulated, solder-less connectors
Receptacle- device used for receiving electrical
plugs
Switch- device used to stop the flow of
electricity
Duplex Receptacle- both outlets are on same
circuit
Single-Pole Switch- designed to be the only
switch in the circuit
Knock Out- partially punched impression
Ground Clip- attaches ground wire to a box
Testing a Circuit:
Continuity Tester- device used to determine if
electricity can flow
between 2 points
Continuity- connected-ness
3 way switch- permits a light/receptacle to be
controlled from 2 locations