Transcript Part 1 - Online Training

ELECTRICAL
SAFETY
Part 1: Basic Electricity
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WHAT IS ELECTRICITY?
Negatively charged
particles (electrons)
moving through
a conductor.
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ELECTRIC CURRENT (I)
Movement of electrons (electric charge)
along a conductor.
Ampere (I) - a measure of the number of
electrons that are moving through a
conductor every second.
1 amp = 6.24 x 1018 electrons per second.
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CONVENTIONAL CURRENT
Electrons flow from negative to positive attracted to the positive terminal and
repelled from the negative terminal.
Although it really doesn’t exist, conventional
current assumes that current flows out of the
positive terminal, through the circuit and into
the negative terminal of the source.
Many references use the conventional
current direction.
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ELECTRICAL CONDUCTOR
A material that has a low resistance
to the flow of electricity.
Metals
Concrete
Graphite
Dirty water
Electricity needs a conductor to move.
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ELECTRICAL INSULATOR
A material that has a high resistance
to the flow of electricity.
Glass
Rubber
Porcelain
Air
Dry wood
Ceramic
Oil
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RESISTANCE (R)
The opposition to the flow of electrons.
Measured in ohms (Ω)
The amount of resistance depends on
type of material
diameter
temperature
length
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RESISTANCE (R)
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POTENTIAL DIFFERENCE
The difference in electrical charge
between two points in a circuit expressed
in volts.
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VOLTAGE (E)
The force or energy that causes the electrical
charge to move through a conductor.
Pressure
Volts
Voltage is the measure of the potential difference
between two points or the potential to move
electrons. It is supplied by a battery or a generator.
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OHM’S LAW
Mathematical formula that describes the
relationship between voltage, current, and
resistance.
Current
Resistance
Voltage
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I = E/R
R = E/I
E = IR (or V = IR)
OHM’S LAW
E
I
E
R
I
R
R = E/I
E
E
I
R
I = E/R
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I
R
E = IR
OHM’S LAW
Water Pipe Analogy
Pressure increase
Flow rate increase
Resistance same
Voltage increase
Current increase
Resistance same
Pressure same
Flow rate decrease
Resistance increase
Voltage same
Current decrease
Resistance increase
Pressure decrease
Flow rate same
Resistance decrease
Voltage decrease
Current same
Resistance decrease
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ELECTRICAL POWER (P)
Power is the rate at which electrical energy
is converted to some other form of energy
such as light, heat, or horsepower.
It is expressed in watts or kilowatts.
P = IE
A 17-watt fluorescent bulb may
produce more light than a 100watt incandescent bulb.
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WATTS, AMPS, OHMS, VOLTS
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ELECTRICAL POWER
Calculate the power
EI=P
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E2 /R = P
I2 R = P
ELECTRICAL POWER
EI=P
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Calculate the power
I2 R = P
E2 /R = P
ELECTROMAGNETIC FIELD
The flow of electricity through a conductor
produces an electric field and a magnetic field
around the conductor.
Electric Field
The electric field is measured in volts
per meter and the higher the source
voltage, the higher strength of the
field. It decreases with distance
from the source.
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ELECTROMAGNETIC FIELD
Magnetic Field
The strength of a magnetic
field is measured in
units of gauss and varies
with the amount of
current moving through
the conductor.
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ELECTROMAGNETIC FIELD
Electric fields are blocked by walls, houses, trees,
soil, and other dense objects.
Magnetic fields pass easily through most objects
and are only blocked by structures containing
large amounts of iron or iron alloy metals.
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ELECTROMAGNET
Electromagnets are important in the operation of
generators, motors, transformers and relays.
They are made by wrapping an
insulated conductor wire around
an iron object and then passing
an electrical current through the
wire.
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DIRECT CURRENT (DC)
Direct currents are produced when the electrons
move in one direction.
Direct current is produced by batteries, solar
panels, fuel cells, and special DC generators such
as wind turbines.
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ALTERNATING CURRENT (AC)
An alternating current reverses direction in a
circuit at regular intervals.
+
–
AC power is represented by a sine wave which
changes 60 times every second.
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ALTERNATING CURRENT (AC)
Voltage continually changes from positive to
negative. The rate of change is measured in
Hertz (cycles per second).
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THREE PHASE AC
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CIRCUITS
The three components of an electrical circuit:
source of power, a path for current, and a load.
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CIRCUITS
Circuit with controller (switch)
Is the circuit open or closed?
On or off?
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CIRCUIT DIAGRAM
A basic circuit diagram
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CIRCUIT SYMBOLS
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DRAW THIS CIRCUIT
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SERIES CIRCUITS
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PARALLEL CIRCUITS
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SHORT CIRCUIT
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SHORT CIRCUIT
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CIRCUIT WIRING
Electrically common points: 1 and 2 and 3 and 4
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CIRCUIT WIRING
Voltage same between points 1 and 4 (across battery),
and between points 2 and 3 (across resistor)
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CIRCUIT WIRING
Electrically common points: 1, 2, and 3 and 4, 5, and 6
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GROUNDING
If there is a short circuit, grounding enables the
electricity to take an alternate path back to
the circuit breaker
and then to a
grounding
rod driven into the
ground.
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GROUNDING
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CIRCUIT BREAKER
A circuit breaker has a
bimetal strip that heats
and bends during a circuit
overload. It then trips the
breaker and opens the
switch.
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CIRCUIT BREAKER
Another type circuit breaker has an
electromagnet. Increasing current boosts the
electromagnet's magnetic force, and decreasing
current lowers the magnetism.
When the current jumps
to unsafe levels, the
electromagnet is strong
enough to pull down a
metal lever connected
to the switch linkage.
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FUSES
Plug fuses are round and screw into a base in a fuse
holder to complete the circuit. It contains a soft
wire or metal that will carry a given amount of
current.
If more current flows in the
circuit than the fuse is
designed to carry, the
metal strip melts or “burns
out” which opens the circuit.
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FUSES
Cartridge fuses fit in between two holders
on each end of the fuse. the metal ends of the
fuse connect to the fuse link inside the cartridge.
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CAPACITOR
Capacitors are
voltage storage
devices.
Camera flash capacitor
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TRANSFORMERS
Power cube transformer
This transformer converts
normal 120 volt AC current
to 3 volts
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Large power transformer
This transformer steps up
voltage to as high as 765,000
volts so it can travel long
distances
TRANSFORMERS
This transformer on the
utility pole receives voltage
from a substation where the
voltage was reduced.
This transformer transforms
7,200 volts to 220-240 volts.
It is then sent to your home
over 3 wires: one ground
and 2 positive.
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TRANSFORMERS
Primary
Coil
Large power transformer
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Secondary
Coil
Power cube transformer
TRANSFORMERS
Reverse side of power cube transformer
Two diodes wrapped in rubber insulation turn AC
current into DC current.
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INSULATED TOOLS
Cable Shears
Pliers
Screwdrivers
Knives
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TESTERS
Non- Contact AC
Voltage Detector
Socket Tester
Clamp-On
Ammeter
Voltage Tester
Non-Contact
Current Detector
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MEASURING INSTRUMENTS
Megohmmeter
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Multimeter
Battery/Bulb/Fuse/
Continuity Tester