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ELECTRICALELECTRICAL

SAFETYSAFETY

ELECTRICALELECTRICAL

SAFETYSAFETY

Part 1: Basic ElectricityPart 1: Basic Electricity

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WHAT IS ELECTRICITY?

Negatively charged particles (electrons) moving througha 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 CONDUCTORA material that has a low resistance to the flow of electricity.

MetalsConcreteGraphiteDirty 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.

GlassRubberPorcelainAirDry woodCeramicOil

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RESISTANCE (R)

The opposition to the flow of electrons. Measured in ohms (Ω)

The amount of resistance depends ontype of materialdiametertemperaturelength

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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.

Volts

Pressure

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 therelationship between voltage, current, and resistance.

Current I = E/R

Resistance R = E/I

Voltage E = IR (or V = IR)

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OHM’S LAW

E E

I R I R

E

I R

E

I R

R = E/I

E = IRI = E/R

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OHM’S LAWWater Pipe Analogy

Pressure increase Voltage increaseFlow rate increase Current increaseResistance same Resistance same

Pressure same Voltage sameFlow rate decrease Current decrease Resistance increase Resistance increase

Pressure decrease Voltage decreaseFlow rate same Current sameResistance decrease Resistance decrease

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ELECTRICAL POWER (P)Power is the rate at which electrical energyis converted to some other form of energysuch as light, heat, or horsepower.

It is expressed in watts or kilowatts.

A 17-watt fluorescent bulb may produce more light than a 100-watt incandescent bulb.

P = IE

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WATTS, AMPS, OHMS, VOLTS

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ELECTRICAL POWER

Calculate the power

E I = P E2 /R = P I2 R = P

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ELECTRICAL POWER

Calculate the powerE I = P E2 /R = P I2 R = P

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ELECTROMAGNETIC FIELD

The flow of electricity through a conductorproduces an electric field and a magnetic fieldaround the conductor.

Electric FieldThe electric field is measured in volts per meter and the higher the source voltage, the higher strength of the field. It decreases with distancefrom the source.

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ELECTROMAGNETIC FIELD

Magnetic FieldThe strength of a magnetic field is measured inunits of gauss and varieswith the amount ofcurrent 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 objectsand are only blocked by structures containinglarge 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 electronsmove in one direction.

Direct current is produced by batteries, solar panels, fuel cells, and special DC generators suchas wind turbines.

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ALTERNATING CURRENT (AC)

An alternating current reverses direction in acircuit at regular intervals.

AC power is represented by a sine wave whichchanges 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 theelectricity to take an alternate path back tothe circuit breakerand then to a groundingrod driven into the ground.

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GROUNDING

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CIRCUIT BREAKER

A circuit breaker has a bimetal strip that heatsand bends during a circuit overload. It then trips the breaker and opens theswitch.

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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 softwire or metal that will carry a given amount ofcurrent.

If more current flows in thecircuit than the fuse isdesigned to carry, the metal strip melts or “burnsout” 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 thefuse connect to the fuse link inside the cartridge.

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CAPACITOR

Capacitors arevoltage storagedevices.

Camera flash capacitor

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TRANSFORMERS

Power cube transformer

This transformer converts normal 120 volt AC current to 3 volts

Large power transformer

This transformer steps up voltage to as high as 765,000 volts so it can travel long distances

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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

Power cube transformerLarge power transformer

PrimaryCoil

SecondaryCoil

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TRANSFORMERS

Reverse side of power cube transformer

Two diodes wrapped in rubber insulation turn AC current into DC current.

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Cable Shears

Pliers Screwdrivers

INSULATED TOOLS

Knives

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Voltage Tester Non-ContactCurrent Detector

Non- Contact AC Voltage Detector

TESTERS

Socket Tester Clamp-On Ammeter

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MEASURING INSTRUMENTS

Megohmmeter Multimeter Battery/Bulb/Fuse/Continuity Tester