Electrical Safety Malagement

OVERVIEW

Motors

Lights

Heaters

120Watt Bulb = 1 Amp X 120 Volts

Voltage, Current, Resistance

Volts=Current (I) x Resistance (R)

Current (I) = Volts x Resistance (R)

Current (I) = Volts x Resistance (R)

How Electricity Works

Operating an electric switch is like turning on a water faucet. Behind the faucet or switch there must be a source of water or electricity with something to transport it, and with a force to make it flow.

In the case of water the source is a pump, and the force to make it flow through the pipes is provided by the pump.

For electricity, the source is the power generator. Current travels through electrical conductors (wires) and the force to make it flow, measured in volts, is provided by a generator.

Electrical Shock

Received when current passes through the bodyYou become part of the

circuitSeverity of a shock

depends on:Path of current through

the bodyAmount of current

flowing through the bodyLength of time the body

is in the circuit

If Electrocution OccursCall for helpDO NOT touch the victim or the conductorShut off the current at the control boxIf the shutoff is not immediately available,

use a non-conducting material to free the victim

If necessary and you know how, begin CPR when current is stopped

In dealing with electricity, never exceed your expertise

Electrical Burns Most common shock-

related, nonfatal injuryOccurs when you

touch electrical wiring or equipment that is improperly used or maintained

Typically occurs on the hands

Very serious injury that needs immediate attention

Controlling Electrical HazardsMost electrical

mishaps are caused by a combination of three factors:• Unsafe equipment

and/or installation, • Workplaces made

unsafe by the environment

• Unsafe work practices

Clues that Electrical Hazards Exist Tripped circuit breakers or blown fuses

Warm tools, wires, cords, connections, or junction boxes

GFCI that shuts off a circuit

Worn or frayed insulation around wire or connection

Overload HazardsIf too many devices are

plugged into a circuit, the current will heat the wires to a very high temperature, which may cause a fire

If the wire insulation melts, arcing may occur and cause a fire in the area where the overload exists, even inside a wall

Preventing Electrical Hazards

• Ways of protecting workers and preventing electrical hazards are:

• Insulation• Grounding• Electrical protective devices (GFCI)• Safe work practices

InsulationCheck insulation prior

to using cables, tools, or equipment

Remove from service any tools or equipment with damaged insulation

Cabinets, Boxes, and Fittings

Junction boxes, pull boxes and fittings must have approved covers

Unused openings in cabinets, boxes and fittings must be closed (no missing knockouts)

29 CFR 1910.305(b)(1) and (2)

GroundingGrounding creates a

low-resistance path from a tool to the earth to disperse unwanted current

When a short or lightning occurs, energy flows to the ground, protecting you from electrical shock, injury and death

Improper GroundingTools plugged into

improperly grounded circuits may become energized

Broken wire or plug on extension cord

Some of the most frequently violated OSHA standards

Hand-Held Electric ToolsHand-held electric tools pose

a potential danger because they make continuous contact with the hand

To protect you from shock, burns, and electrocution, tools must:Have a three-wire cord with

ground and be plugged into a grounded receptacle, or

Be double insulated

Panel BoxesPanel boxes are used to house circuit

breakers that block or isolate energy Ensure panel boxes remain clear Label all circuits for what they control Label panel boxes for what they control Replace circuit breakers with blanks when not

in use

CHAPTER 2

UNDERSTANDING ELECTICITY

Basic Electronics (Outline)The Elements of ElectricityVolt-Ohm-Meter Basics (Measuring Electricity)Circuit Diagrams Basics (Electronic

Roadmaps)The ResistorOhm’s LawThe CapacitorThe InductorThe DiodeThe Transistor (Electronic Valve)

The Elements of ElectricityVoltageCurrentResistanceTypes of Current: AC and DCCircuits

ClosedOpenShort

Voltage, Current, and Resistance Water flowing through a

hose is a good way to imagine electricity

Water is like Electrons in a wire (flowing electrons are called Current)

Pressure is the force pushing water through a hose – Voltage is the force pushing electrons through a wire

Friction against the holes walls slows the flow of water – Resistance is an impediment that slows the flow of electrons

Forms of CurrentThere are 2 types of current

The form is determined by the directions the current flows through a conductor

Direct Current (DC)Flows in only one direction from negative toward

positive pole of source

Alternating Current (AC)Flows back and forth because the poles of the source

alternate between positive and negative

AC Current Vocabulary

Time Period of One Cycle

CircuitsA circuit is a path for current to flowThree basic kinds of circuits

Open – the path is broken and interrupts current flow

Closed – the path is complete and current flows were it is intended

Short – an unintended low resistance path that divers current

Circuits

Volt-Ohm-Meter (VOM) Basics (Measuring Electricity)

Common FunctionsVoltage

AC/DC Ranges

Current AC/DC Ranges

Resistance (DC only) Ranges Continuity

Semi-conductor Performance Transistors Diodes

Capacitance

Meter Reading Digits

DC Voltage Scales

AC Voltage Scales

Jacks

Function Selection

Resistance

DC Current (low)

DC Current (high)

Transistor Checker

Diode Checker

Negative

Source

Positive

Source

Measuring ResistanceWhen the VOM is used to measure

resistance, what actually is measured is a small current applied to the component.

There are 5 ranges. An out of resistance reading will be indicated by a single “1” digit. Remember k means multiply the reading by 1000.

Operating voltages should be removed from the component under test or you could damage the VOM at worst, or the reading could be in error at best.

Circuit Diagrams Basics (Electronic Roadmaps)

Component RepresentationsResistorGroundCapacitorInductorDiodeTransistorIntegrated circuitSpecial

Vcc1

Gnd8

GP52

GP07

GP43

GP16

GP34

GP25

12F6

75

Out

Gnd

Vcc

4.7K

SW5N.O.

78L05+9V

Ou

t

Gn

d

In

.1uF

SW6

Note: Internal pull-up resistors are used on 12F265 pins

GP0, GP1, GP2, GP4, GP5 External pull-up resistor required on GP3 Protection diodes are internal to K1 - K4 Switchs SW1 - SW4 are internal to K1 - K4

Project T.V. Remote Decoder Circuit

330

1N4001

+5 Voltsto Relays

330

2N3904

+5V

K1

SW1

LED

4.7K

330

2N3904

+5V

K2

SW2

LED

4.7K

330

2N3904

+5V

K3

SW3

LED

4.7K

330

2N3904

+5V

K4

SW4

LED

4.7K

Fixed Variable

EarthChassis

Fixed Variable

Air Core Iron CoreVariable

General PurposeZener

Light Emitting

(LED)

NPN PNP FET

2

3

4

5

13

12

11

10

7 8

1 14

6 9

V

A

Battery Speaker

Voltmeter

AmpmeterAntennaFuse

The ResistorResistance definedResistance values

Ohms – color code interpretationPower dissipation

Resistors in circuitsSeriesParallelCombination

Resistance DefinedResistance is the impediment to the flow of

electrons through a conductor(friction to moving electrons)Where there’s friction, there is heat generatedAll materials exhibit some resistance, even the

best of conductorsUnit measured in Ohm(s)

From 1/10 of Ohms to millions of Ohms

Resistor TypesFixed ValueVariable valueComposite resistive materialWire-woundTwo parameters associated with resistors

Resistance value in OhmsPower handling capabilities in watts

1/8 ¼ ½ 1 2 20

Reading Resistor Color Codes

1. Turn resistor so gold, silver band, or space is at right

2. Note the color of the two left hand color bands3. The left most band is the left hand value digit4. The next band to the right is the second value

digit5. Note the color of the third band from the left,

this is the multiplier6. Multiply the 2 value digits by the multiplier

Reading Resistor Color Codes(Practice Problems)1. Orange, orange, red?2. Yellow, violet, orange?3. Brown, black, brown?4. Brown, black, green?5. Red, red, red?6. Blue, gray, orange?7. Orange, white, orange?

Power dissipationResistance generates heat and the

component must be able to dissipate this heat to prevent damage.

Physical size (the surface area available to dissipate heat) is a good indicator of how much heat (power) a resistor can handle

Measured in wattsCommon values ¼, ½, 1, 5, 10 etc.

Resistors in CircuitsSeriesLooking at the

current path, if there is only one path, the components are in series.

nE RRRR 21

R1 R2 Calculated RE

Measured RE

100 100

100K 10K

4.7K 4.7K

330 4.7K

Resistors in CircuitsParallel

If there is more than one way for the current to complete its path, the circuit is a parallel circuit.

n

E

RRRRR

RRR

1111

21

21

21

R1 R2 Calculated RE

Measured RE

100 100

100K 10K

4.7K 10K

330 4.7K

Resistors in CircuitsParallel Challenge

Make a circuit with 3 resistors in parallel, calculate the equivalent resistance then measure it. R1 = 330 ohm

R2 = 10 k-ohm

R3 = 4.7 k-ohm

Resistors in CircuitsMixed

If the path for the current in a portion of the circuit is a single path, and in another portion of the circuit has multiple routes, the circuit is a mix of series and parallel.

Ser

ies

Ser

ies

Parallel


Take the parallel segment of the circuit and calculate the equivalent resistance:

R1 330

R2

4.7K

R3

2.2K

32

32

RR

RRRE

Resistors in CircuitsMixedWe now can look at

the simplified circuit as shown here. The parallel resistors have been replaced by a single resistor with a value of 1498 ohms.

Calculate the resistance of this series circuit:

ERR 1

RE=1498

R1 330

Resistors in CircuitsMixedIn this problem,

divide the problem into sections, solve each section and then combine them all back into the whole.

R1 = 330R2 = 1KR3 = 2.2KR4 = 4.7K

Ser

ies

Par

alle

l

Ser

ies

R1

R2

R3

R4

Resistors in CircuitsMixedLooking at this

portion of the circuit, the resistors are in series. R2 = 1k-ohm

R3 = 2.2 k-ohm

R2

R3

32 RRRE


Substituting the equivalent resistance just calculated, the circuit is simplified to this. R1 = 330 ohm

R4 = 4.7 k-ohm

RE = 3.2 k-ohm

Now look at the parallel resistors RE and R4.

R1

RE R4


Using the parallel formula for: RE = 3.2 k-ohm

R4 = 4.7 k-ohm

RER4

4

4

RR

RRR

E

ET


The final calculations involve R1 and the new RTotal from the previous parallel calculation. R1 = 330

RE = 1.9K

R1

RTotal

ETotal RRR 1

R1 = 330 ohm

R2 = 1 k-ohm

R3 = 2.2 k-ohm

R4 = 4.7 k-ohm

RTotal = 2,230

=

Ohm’s LawThe mathematical relationship

E=I*RDoing the mathKirchhoff’s law

A way to predict circuit behavior It all adds up Nothing is lost

Ohm’s LawThere is a

mathematical relationship between the three elements of electricity. That relationship is Ohm’s law. E = volts R = resistance in ohms I = current in amps

RIE *

I

ER

R

EI

Ohm’s LawThis is the basic

circuit that you will use for the following exercises.

The VOM will be moved to measure voltage,resistance and current.

A

V

Ohm’s Law Exercise 1Wire this circuit

using a 100 ohm resistor.

Without power applied measure the resistance of the resistor.

Connect the 9 volt battery and measure the voltage across the resistor.

Record your data.

V

Ohm’s Law Exercise 1Using the voltage

and resistance data in Ohm’s law, calculate the anticipated current.

Example data results in a current of .09 amps or 90 milliamps

R

EI

ohms

voltsamps

1.98

8.809.

Ohm’s Law Exercise 1Insert the VOM into

the circuit as indicated in this diagram.

Using the appropriate current range, measure the actual current in the circuit.

How does the measured current compare to your prediction using Ohm’s law?

A

Ohm’s Law In PracticeThe next series of exercises will put

Ohm’s Law to use to illustrate some principles of basic electronics.

As in the previous exercise you will build the circuits and insert the VOM into the circuit in the appropriate way to make current and voltage measurements.

Throughout the exercise record your data so that you can compare it to calculations.

Ohm’s Law In PracticeBuild up the

illustrated circuit. R1 = 1 k-ohm

R2 = 1 k-ohm

R3 = 2.2 k-ohm

R4 = 300 ohm

Measure the current flowing through the circuit.

R1

R2R3

R4

A

+ -

Ohm’s Law In PracticeNow move the

VOM to the other side of the circuit and measure the current.

The current should be the same as the previous measurement.

A

+ -

Ohm’s Law In PracticeInsert the VOM at

the indicated location and measure the current.

There should be no surprise that the current is the same.

A

+

-

Ohm’s Law In PracticeMeasure the voltage

across R1.Using Ohm’s law,

calculate the voltage drop across a 1K ohm resistor at the current you measured

Compare the result.

V

Ohm’s Law In PracticeIn this next step, you

will insert the VOM in the circuit at two places illustrated at the right as #1 and #2.

Record your current readings for both places.

Add the currents and compare and contrast to the current measured entering the total circuit.

A A

#1 #2

Ohm’s Law In PracticeUsing the current measured through #1

and the resistance value of R2, 1k ohms, calculate the voltage drop across the resistor.

Likewise do the same with the current measured through #2 and the resistance value of R3, 2.2k ohms.

Compare and contrast these two voltage values

Ohm’s Law In PracticeMeasure the voltage

across the parallel resistors and record your answer.

Compare and contrast the voltage measured to the voltage drop calculated.

V

Ohm’s Law In PracticeIn the next step,

insert the VOM into the circuit as illustrated, measure and record the current.

Compare and contrast the current measured to the total current measured in a previous step.

Were there any surprises?

A

Ohm’s Law In PracticeUsing the current you

just measured and the resistance of R4 (330 ohms), calculate what the voltage drop across R4 should be.

Insert the VOM into the circuit as illustrated and measure the voltage.

Compare and contrast the measured and calculated voltages.

V

Ohm’s Law In PracticeThere is one final

measurement to complete this portion of the exercise. Insert the VOM as indicated.

Recall the 3 voltages measured previously; across R1, R2 and R3, and across R4.

Add these three voltages together and then compare and contrast the result with the total voltage just measured.

V

Ohm’s Law In PracticeWhat you observed was:

The sum of the individual currents entering a node was equal to the total current leaving a node .

The sum of the voltage drops was equal to the total voltage across the circuit.

This is Kirchhoff’s law and is very useful in the study of electronic circuits.

You also noted that Ohm’s law applied throughout the circuit.

The CapacitorCapacitance

definedPhysical

constructionTypesHow construction

affects valuesPower ratings

Capacitor performance with AC and DC currents

Capacitance valuesNumbering system

Capacitors in circuitsSeriesParallelMixed

The CapacitorDefinedA device that stores

energy in electric field.Two conductive plates

separated by a non conductive material.

Electrons accumulate on one plate forcing electrons away from the other plate leaving a net positive charge.

Think of a capacitor as very small, temporary storage battery.

The Capacitor Physical Construction

Capacitors are rated by:Amount of charge that

can be held.The voltage handling

capabilities.Insulating material

between plates.

The CapacitorAbility to Hold a Charge

Ability to hold a charge depends on:Conductive plate

surface area.Space between plates.Material between

plates.

Charging a Capacitor In the following activity

you will charge a capacitor by connecting a power source (9 volt battery) to a capacitor.

You will be using an electrolytic capacitor, a capacitor that uses polarity sensitive insulating material between the conductive plates to increase charge capability in a small physical package.

Notice the component has polarity identification + or -.

+

Charging a CapacitorTouch the two leads of the capacitor

together.This short circuits the capacitor to make sure

there is no residual charge left in the capacitor.

Using your VOM, measure the voltage across the leads of the capacitor

Charging a CapacitorWire up the illustrated

circuit and charge the capacitor.

Power will only have to be applied for a moment to fully charge the capacitor.

Quickly remove the capacitor from the circuit and touch the VOM probes to the capacitor leads to measure the voltage.

Carefully observe the voltage reading over time until the voltage is at a very low level (down to zero volts).

+

The CapacitorBehavior in DC

When connected to a DC source, the capacitor charges and holds the charge as long as the DC voltage is applied.

The capacitor essentially blocks DC current from passing through.

The CapacitorBehavior in ACWhen AC voltage is applied, during one

half of the cycle the capacitor accepts a charge in one direction.

During the next half of the cycle, the capacitor is discharged then recharged in the reverse direction.

During the next half cycle the pattern reverses.

It acts as if AC current passes through a capacitor

The CapacitorBehavior

A capacitor blocks the passage of DC current

A capacitor passes AC current

The CapacitorCapacitance Value

The unit of capacitance is the farad.A single farad is a huge amount of capacitance.Most electronic devices use capacitors that are a

very tiny fraction of a farad.

Common capacitance ranges are: Micro 10-6

Nano 10-9

Pico 10-12

pn

The CapacitorCapacitance ValueCapacitor

identification depends on the capacitor type.

Could be color bands, dots, or numbers.

Wise to keep capacitors organized and identified to prevent a lot of work trying to re-identify the values.

Capacitors in CircuitsThree physical

factors affect capacitance values.Plate spacingPlate surface areaDielectric material

In series, plates are far apart making capacitance less

+

-

Charged plates far apart

21

21

CC

CCCE

Capacitors in CircuitsIn parallel, the

surface area of the plates add up to be greater.

This makes the total capacitance higher.

+

-

21 CCCE

The InductorInductance definedPhysical

constructionHow construction

affects values

Inductor performance with AC and DC currents

The Inductor There are two fundamental principles of

electromagnetics:1. Moving electrons create a magnetic field.2. Moving or changing magnetic fields cause

electrons to move. An inductor is a coil of wire through which

electrons move, and energy is stored in the resulting magnetic field.

The InductorLike capacitors,

inductors temporarily store energy.

Unlike capacitors: Inductors store energy in a

magnetic field, not an electric field.

When the source of electrons is removed, the magnetic field collapses immediately.

The InductorInductors are simply

coils of wire.Can be air wound (just

air in the middle of the coil)

Can be wound around a permeable material (material that concentrates magnetic fields)

Can be wound around a circular form (toroid)

The InductorInductance is measured in Henry(s).A Henry is a measure of the intensity of the

magnetic field that is produced.Typical inductor values used in electronics

are in the range of millihenry (1/1000 Henry) and microhenry (1/1,000,000 Henry)

The InductorThe amount of

inductance is influenced by a number of factors:Number of coil turns.Diameter of coil.Spacing between turns.Size of the wire used.Type of material inside

the coil.

Inductor Performance With DC CurrentsWhen a DC current is applied to an

inductor, the increasing magnetic field opposes the current flow and the current flow is at a minimum.

Finally, the magnetic field is at its maximum and the current flows to maintain the field.

As soon as the current source is removed, the magnetic field begins to collapse and creates a rush of current in the other direction, sometimes at very high voltage.

Inductor Performance With AC CurrentsWhen AC current is applied to an

inductor, during the first half of the cycle, the magnetic field builds as if it were a DC current.

During the next half of the cycle, the current is reversed and the magnetic field first has to decrease the reverse polarity in step with the changing current.

These forces can work against each other resulting in a lower current flow.

The InductorBecause the magnetic

field surrounding an inductor can cut across another inductor in close proximity, the changing magnetic field in one can cause current to flow in the other … the basis of transformers

The DiodeThe semi-conductor phenomenaDiode performance with AC and DC currentsDiode types

General purposeLEDZenier

The DiodeThe semi-conductor phenomena

Atoms in a metal allow a “sea” of electrons that are relatively free to move about.

Semiconducting materials like Silicon and Germanium have fewer free electrons.

Impurities added to semiconductor material can either add free electrons or create an absence of free electrons (holes).


Consider the bar of silicon at the right. One side of the bar is doped with negative material (excess

electrons). The cathode. The other side is doped with positive material (excess

holes). The anode In between is a no man’s land called the P-N Junction.


Consider now applying a negative voltage to the anode and positive voltage to the cathode.

The electrons are attracted away from the junction.

This diode is reverse biased meaning no current will flow.

The Diode The semi-conductor phenomena

Consider now applying a positive voltage to the anode and a negative voltage to the cathode.

The electrons are forced to the junction.This diode is forward biased meaning

current will flow.

The Diodewith AC CurrentIf AC is applied to a diode:

During one half of the cycle the diode is forward biased and current flows.

During the other half of the cycle, the diode is reversed biased and current stops.

This is the process of rectification, allowing current to flow in only one direction.

This is used to convert AC into pulsating DC.

Input AC Voltage

Output Pulsed DC Voltage

Diode conducts

Diode off

The Light Emitting DiodeIn normal diodes, when electrons combine

with holes current flows and heat is produced.

With some materials, when electrons combine with holes, photons of light are emitted, this forms an LED.

LEDs are generally used as indicators though they have the same properties as a regular diode.

The Light Emitting DiodeBuild the illustrated circuit

on the proto board.The longer LED lead is the

anode (positive end).Observe the diode

responseReverse the LED and

observe what happens.The current limiting

resistor not only limits the current but also controls LED brightness.

330

Zener DiodeA Zener diode is

designed through appropriate doping so that it conducts at a predetermined reverse voltage. The diode begins to

conduct and then maintains that predetermined voltage

The over-voltage and associated current must be dissipated by the diode as heat

9V 4.7V

The Transistor (Electronic Valves)

How they works, an inside look

Basic typesNPNPNP

The basic transistor circuitsSwitchAmplifier

base

collector

emitter

N P Ncollector emitter

base

e - e -forward bias

conducting e -

The base-emitter current controls the collector-base current

N P Ncollector emitter

base

e - e -reverse bias

non-conducting

The TransistorThere are two basic types

of transistors depending of the arrangement of the material. PNP NPN

An easy phrase to help remember the appropriate symbol is to look at the arrow. PNP – pointing in proudly. NPN – not pointing in.

The only operational difference is the source polarity.

PNP

NPN

CHAPTER 3

ELECTRICAL HARM

IntroductionThere are four main types of electrical

injuries:Electrocution (death due to electrical shock)Electrical shockBurnsFalls

189

Electrical ShockReceived when current passes

through the bodySeverity of the shock depends on:

Path of current through the body

Amount of current flowing through the body

Length of time the body is in the circuit

LOW VOLTAGE DOES NOT MEAN LOW HAZARD

190

Dangers of Electrical ShockCurrents greater than 75 mA*

can cause ventricular fibrillation (rapid, ineffective heartbeat)

Will cause death in a few minutes unless a defibrillator is used

75 mA is not much current – a small power drill uses 30 times as much

191

* mA = milliampere = 1/1,000 of an ampere

Defibrillator in use

How is an electrical shock received?When two wires have different potential

differences (voltages), current will flow if they are connected togetherIn most household wiring, the black wires

are at 110 volts relative to groundThe white wires are at zero volts because

they are connected to groundIf you come into contact with an energized

(live) black wire, and you are also in contact with the white grounded wire, current will pass through your body and YOU WILL RECEIVE A SHOCK

192

How is an electrical shock received?(cont’d)

If you are in contact with an energized wire or any energized electrical component, and also with any grounded object, YOU WILL RECEIVE A SHOCK

You can even receive a shock when you are not in contact with a groundIf you contact both wires of a 240-volt cable,

YOU WILL RECEIVE A SHOCK and possibly be electrocuted

193

Electrical Burns Most common shock-related,

nonfatal injuryOccurs when you touch

electrical wiring or equipment that is improperly used or maintained

Typically occurs on the handsVery serious injury that

needs immediate attention

194

FallsElectric shock can also

cause indirect or secondary injuries

Workers in elevated locations who experience a shock can fall, resulting in serious injury or death

195

Inadequate Wiring Hazards A hazard exists when a

conductor is too small to safely carry the current

Example: using a portable tool with an extension cord that has a wire too small for the toolThe tool will draw more

current than the cord can handle, causing overheating and a possible fire without tripping the circuit breaker

The circuit breaker could be the right size for the circuit but not for the smaller-wire extension cord

196

Wire Gauge

WIRE

Wire gauge measures wires ranging in size from number 36 to 0 American wire gauge (AWG)

Overload HazardsIf too many devices are

plugged into a circuit, the current will heat the wires to a very high temperature, which may cause a fire

If the wire insulation melts, arcing may occur and cause a fire in the area where the overload exists, even inside a wall

197

Electrical Protective DevicesThese devices shut off electricity flow in

the event of an overload or ground-fault in the circuit

Include fuses, circuit breakers, and ground-fault circuit-interrupters (GFCI’s)

Fuses and circuit breakers are overcurrent devices When there is too much current:

Fuses meltCircuit breakers trip open

198

Ground-Fault Circuit Interrupter This device protects you from

dangerous shock The GFCI detects a difference in

current between the black and white circuit wires (This could happen when electrical equipment is not working correctly, causing current “leakage” – known as a ground fault.)

If a ground fault is detected, the GFCI can shut off electricity flow in as little as 1/40 of a second, protecting you from a dangerous shock

199

Grounding HazardsSome of the most frequently violated OSHA

standardsMetal parts of an electrical wiring system that we

touch (switch plates, ceiling light fixtures, conduit, etc.) should be at zero volts relative to ground

Housings of motors, appliances or tools that are plugged into improperly grounded circuits may become energized

If you come into contact with an improperly grounded electrical device, YOU WILL BE SHOCKED

200

Overhead Powerline HazardsMost people don’t realize that

overhead powerlines are usually not insulated

Powerline workers need special training and personal protective equipment (PPE) to work safely

Do not use metal ladders – instead, use fiberglass ladders

Beware of powerlines when you work with ladders and scaffolding

201

202

Some Examples of Some Examples of OSHA Electrical OSHA Electrical Requirements . . . .Requirements . . . .

Grounding PathThe path to ground

from circuits, equipment, and enclosures must be permanent and continuous

Violation shown here is an extension cord with a missing grounding prong

203

Hand-Held Electric Tools Hand-held electric tools pose a

potential danger because they make continuous good contact with the hand

To protect you from shock, burns, and electrocution, tools must:Have a three-wire cord with

ground and be plugged into a grounded receptacle, or

Be double insulated, orBe powered by a low-voltage

isolation transformer

204

Guarding of Live PartsMust guard live parts of electric

equipment operating at 50 volts or more against accidental contact by: Approved cabinets/enclosures, orLocation or permanent partitions

making them accessible only to qualified persons, or

Elevation of 8 ft. or more above the floor or working surface

Mark entrances to guarded locations with conspicuous warning signs

205

Guarding of Live PartsMust enclose or guard

electric equipment in locations where it would be exposed to physical damage

Violation shown here is physical damage to conduit

206

Cabinets, Boxes, and FittingsJunction boxes, pull boxes

and fittings must have approved covers

Unused openings in cabinets, boxes and fittings must be closed (no missing knockouts)

Photo shows violations of these two requirements

207

More vulnerable than fixed wiringDo not use if one of the recognized

wiring methods can be used instead

Flexible cords can be damaged by:AgingDoor or window edgesStaples or fasteningsAbrasion from adjacent

materialsActivities in the area

Improper use of flexible cords can cause shocks, burns or fire

208

Use of Flexible CordsUse of Flexible Cords

Permissible Uses of Flexible CordsExamples

209

Pendant, orFixture Wiring

Portable lamps,tools or appliances

Stationary equipment-to facilitate interchange

210

Substitute for fixed wiring

Run through walls, ceilings, floors, doors, or windows

Concealed behind or attached to building surfaces

Clues that Electrical Hazards Exist Tripped circuit breakers or blown fusesWarm tools, wires, cords, connections, or

junction boxesGFCI that shuts off a circuitWorn or frayed insulation around wire or

connection

211

Training

Deenergizing electric equipment before inspecting or making repairs

Using electric tools that are in good repairUsing good judgment when working near

energized linesUsing appropriate protective equipment

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Train employees working with electric equipment in safe work practices, including:

SummaryHazardsInadequate wiringExposed electrical partsWires with bad insulationUngrounded electrical

systems and toolsOverloaded circuitsDamaged power tools

and equipmentUsing the wrong PPE and

toolsOverhead powerlinesAll hazards are made

worse in wet conditions

Protective MeasuresProper groundingUsing GFCI’sUsing fuses and circuit

breakersGuarding live partsProper use of flexible

cordsTraining

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CHAPTER 4

ELECTRICAL HAZARDS

Electrical HazardsBare conductorsInsulation failureEquipment failureStatic electricityHeating and overheatingElectrical explosions

Bare ConductorsLive overhead wires most commonWorking on rooftopsRepair of electrical systemsCapacitors

Insulation FailureHeat and elevated temperaturesMoisture and humidityMechanical damageRodents, fungiChemical

incompatibility

Equipment FailureOlder portable toolsEnergized housingBroken connectionsWrongly replaced internal wiringLack of grounding plug

Static ElectricityOccurs when two different materials contact

and then separateHigh voltage, low currentFlammable liquidsLightning

Heating and OverheatingUse of electricity results in heatCan cause accidental firesBurns out equipment

Equipment failure and ignitionHot surfaces

Electrical ExplosionsRapid overheating from overcurrentsCaused by short circuits, power surges, or

lightningHeated contaminants in oil-filled

breakers or transformersCapacitors subject to wrong polarity

It’s Your Job to Know!It’s Your Job to Know! Know the hazards of electricity Know the equipment Use Safe Work Practices Inspect your PPE before each use Don’t work on energized circuits without permission

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Safety-Related Safety-Related Work PracticesWork Practices

To protect workers from electrical shock:Use barriers and guards to prevent

passage through areas of exposed energized equipment

Pre-plan work, post hazard warningsand use protective measures

Keep working spaces and walkways clear of cords

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“An employee working on a roof made contact with the service entrance riser into the home and was electrocuted…”

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Special Training is required for work on electrical equipment. Such training is for Authorized Employees and it covers:Safe Work Practices Isolation of Electrical Sources Test Equipment Tools & PPE

Only Authorized Employees may conduct electrical work

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CautionCaution

Control DevicesControl DevicesControl circuit devices such as…push buttons selector switches interlocks

… may not be used as the sole means for de-energizing circuits or equipment.

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Control – Use GFCIControl – Use GFCI(ground-fault circuit interrupter)(ground-fault circuit interrupter)

Protects you from shockDetects difference in current

between the black and white wires

If ground fault detected, GFCI shuts off electricity in 1/40th of a second

Use GFCI’s on all 120-volt, single-phase, 15- and 20-ampere receptacles, or have an assured equipment grounding conductor program.

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ELECTRICAL SAFETYELECTRICAL SAFETY Effects of Amount of AC Current ma=1/1000th of an amp

3 ma- painful shock which cause indirect accidents

10ma- muscle contraction...”no let go” danger

30ma- lung paralysis- usually temporary50ma- possible ventricular fibrillation

(heart dysfunction, usually fatal)100 ma- certain ventricular fibrillation,

fatal4 amps- heart paralysis, severe burns

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How it worksHow it works

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Are these safe practices?Are these safe practices?

230

Lock & TagLock & TagLock & Tag all Sources

Place Lock & Tag on each disconnecting means used to de-energize circuits

Attach lock to prevent operating the disconnecting means

Place Tag with each lock

Note: Only the person who places the lock may remove it.

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Lockout Devices

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If a Lock cannot be applied…If a Lock cannot be applied…A tag used without a lock must be

supplemented by at least one additional safety measure that provides a level of safety equal to that of a lock.

Examples: Removal of an isolating circuit

element such as a fuse

Blocking of a controlling switch Opening of an extra disconnecting

device. 233

234

TagoutThere many different kinds of tags and Lockout devices.

Release Stored EnergyRelease Stored EnergyStored electric energy must be released

before starting work.

Discharge all Capacitors

Short-Circuit & Ground all high capacitance elements

235

Is it “Dead”?Is it “Dead”?Verify System is De-

energized Operate the equipment controls to check that equipment cannot berestarted.

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Use test equipment to test the circuits & Use test equipment to test the circuits & electrical parts for voltage & currentelectrical parts for voltage & current

Alerting others of hazardsAlerting others of hazardsUse barricades to prevent or limit access

to work areas with un-insulated energized conductors or circuit parts.

Use safety signs, safety symbols, or accident prevention tags to warn others about electrical hazards which may endanger them.

If signs and barricades do not provide sufficient warning and protection from electrical hazards, an attendant shall be stationed to warn and protect employees.

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238

Electrical ToolsElectrical Toolsand Cordsand Cords

Portable Electric Tools Portable Electric Tools & Cords& CordsPortable equipment must be handled

in a manner which will not cause damage.

Flexible electric cords connected to equipment may not be used for raising or lowering the equipment.

Flexible cords may not be fastened with staples or otherwise hung in such a fashion as could damage the outer jacket or insulation.

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Tools & EquipmentTools & EquipmentUse insulated tools or handling equipment when working near exposed energized conductors or circuit parts.

Use fuse handling equipment to remove or install fuses when the fuse terminals are energized.

Ropes and handlines used near exposed energized parts must be nonconductive.

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Power Tool RequirementsPower Tool Requirements• Have a three-wire cord with

ground plugged into a grounded receptacle, or

• Be double insulated, or

• Be powered by a low-voltage isolation transformer

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Preventing Electrical Hazards - ToolsPreventing Electrical Hazards - ToolsInspect tools before

useUse the right tool

correctlyProtect your toolsUse double insulated

tools

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Double Insulated marking

Any problems?Any problems?

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Clues that Electrical Hazards ExistClues that Electrical Hazards Exist Tripped circuit

breakers or blown fusesWarm tools, wires,

cords, connections, or junction boxes

GFCI that shuts off a circuit

Worn or frayed insulation around wire or connection

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Beware of Old WiringBeware of Old Wiring

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• Removal of expansion tank (hot water).Removal of expansion tank (hot water).• Old style knob electrical wiring.Old style knob electrical wiring.• Victim contacted frayed wiring.Victim contacted frayed wiring.

Wire PullingWire Pulling • Avoid manual wire pulling and use a tugger or a handtool whenever possible• Communication between the puller and feeder to coordinate movements will make the job easier and safer.• Use lighter-weight tools.

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Reducing Body StrainsReducing Body StrainsCHANGE BODY POSITIONS. Working overhead, at floor level, or in

cramped spaces forces the body into awkward postures.

To relieve muscle tension and improve circulation, change body positions, alternate tasks, and stretch throughout the day.

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SummarySummaryElectrical equipment must be:

Listed and labeled Free from hazards Used in the proper manner

If you use electrical tools you must: Be protected from electrical shockUse them in a comfortable position Be provided with necessary safety

equipment

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Always Always remember…remember…

It’s your It’s your lifelife!!

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“A tree trimmer was electrocuted when he touched an overhead electrical line while descending a palm tree…”

“An employee was electrocuted while working on an A/C unit…”

CHAPTER 5

ELECTRICAL PROTECTION

Consequences of an Arc-Flash Incident

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Mitigation of Electrical HazardsWork De-Energized Engineer Out the Hazard Follow Electrical Safe Work Practices

Employ Lockout/Tagout of Hazardous Electrical Energy Sources

Use Voltage Insulating PPE and EquipmentUse PPE for Arc-Flash ProtectionUse Ground Fault Circuit Interrupters

FN000385/CR, Electrical Safety in the Workplace 254

Electrical systems and equipment and all design, construction, installation, inspection, testing, and operational activities shall be in accordance with established electrical safety standards

Electrical work activities at Fermilab are preferentially performed on de-energized circuits

Implementation of Lockout/Tagout (LOTO) procedures is central to our Program

See a Problem? Tell Somebody!

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What is Energized Work?Any activity On or Near exposed energized

conductors where a real hazard exists from contact or equipment failure that can result in electric shock, arc flash burn or arc blast.

Working On - Coming in contact with live parts with the hands, feet, or other body parts, with tools, probes or with test equipment

Working Near – Inside the Limited Approach Boundary

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Diagnostic Energized WorkInspection, testing, voltage and/or current

measurements, phase alignment, troubleshooting, circuit and signal tracing, thermal imaging, etc. that are performed on or near exposed live parts within the Limited Approach Boundary

Verification Associated with LOTO

Performed by Qualified Persons Utilizing Appropriately Rated Measurement Equipment and Required PPE.

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Manipulative Energized WorkMaking, tightening or breaking of

energized electrical connections or the replacement, removal, or addition of electrical or mechanical components

Examples include: Replacing a duplex outlet, light switch,

fluorescent fixture ballast, fuses, circuit breakersDrilling or punching holes in a panelboardPulling conductors into a panelboard

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Working on or near live parts must be justified

Diagnostic Energized Work is allowed when the diagnostic activity is not feasible with the circuit de-energized

Manipulative Energized Work is prohibited at Fermilab unless it can be demonstrated that de-energization introduces additional or increased hazards or is infeasible due to equipment design or operational limitations

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Shock Hazard and ProtectionThere is No One Solution for Protection from

Shock, but Really Pretty Simple

Degree of protection is determined primarily by system voltage and distance from the energized part

260

Shock Protection BoundariesLimited Approach Boundary

Distance from an exposed live part within which a shock hazard exists

Note that this Boundary is significant to Fermilab’s definition of Energized Work

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Restricted Approach BoundaryDistance from an exposed live part within

which there is an increased risk of shock due to electrical arc over, combined with inadvertent movement, for personnel working in close proximity to the live part

Prohibited Approach BoundaryDistance from an exposed live part within

which work is considered the same as making contact with the live part

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Shock ProtectionShock Hazard Analysis

Defined at 130.2 (A)Shock Protection Boundaries

Defined at Table 130.2 (C)

You are Responsible for Establishing, Maintaining, and Communicating to Others the

Extent of these Boundaries



Table 130.2(C) Approach Boundaries to Live Parts for Shock Protection. (All dimensionsare distance from live part to employee.)

Restricted Approach Nominal System -------------------------------------------------------- Boundary; Includes

Exposed Movable Conductor

Exposed Fixed Circuit Part

Inadvertent Movement Adder

Prohibited Approach Boundary

Less than 50 Not specified Not specified Not specified Not specified

50 to 300 10 ft 0 in. 3 ft 6 in. Avoid contact Avoid contact

301 to 750 10 ft 0 in. 3 ft 6 in. 1 ft 0 in. 0 ft 1 in.

751 to 15 kV 10 ft 0 in. 5 ft 0 in. 2 ft 2 in. 0 ft 7 in.

15.1 kV to 36 kV 10 ft 0 in. 6 ft 0 in. 2 ft 7 in. 0ft 10 in.

36.1 kV to 46 kV 10 ft 0 in. 8 ft 0 in. 2 ft 9 in. 1 ft 5 in.

46.1 kV to 72.5 kV 10 ft 0 in. 8 ft 0 in. 3 ft 2 in. 2 ft 1 in.

72.6 kV to 121 kV 10 ft 8 in. 8 ft 0 in. 3 ft 3 in. 2 ft 8 in.

138 kV to 145 kV 11 ft 0 in. 10 ft 0 in. 3 ft 7 in. 3 ft 1 in.






Note: For Flash Protection Boundary, see 130.3(A).See definition in Article 100 and text in 130.2(D)(2) and Annex C for elaboration.

Limited Approach Boundary

Voltage Range, Phase to Phase

Limited Approach BoundaryLimited Approach Boundary (LAB)

3 feet 6 inches for 50 to 750 Volts 5 feet for 13.8 KV 15 feet 4 inches for 345 KV

Occupancy generally limited to Qualified Workers

Unqualified persons may enter if advised of hazards and continuously escorted

Appropriately rated insulated tools and/or equipment must be used if they might (likely) make accidental contact with exposed live parts

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Restricted Approach Boundary Restricted Approach Boundary (RAB)

Avoid Contact for 50 to 300 Volts1 foot for 301 to 750 Volts2 feet 2 inches for 13.8 KV

Occupancy only by Qualified WorkersMay not cross boundary with conductive

objectsNo uninsulated part of the body may cross this

boundaryFor voltages greater than 300 Volts, must

wear PPE for shock protection, such as insulating gloves and insulating sleeves

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Prohibited Approach BoundaryProhibited Approach Boundary (PAB)

Avoid Contact for 50 to 300 Volts1 inch for 301 to 750 Volts7 inches for 13.8 KV

For 50 to 300 Volts, wearing of PPE for shock protection is advised if body contact with exposed live parts is likely


Approach BoundariesLimited Approach Boundary

Restricts the approach of unqualified persons

Restricted and Prohibited Approach Boundaries Restricts the approach of qualified persons

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PPE and Equipment for Shock Protection PPE

Insulating Gloves, Matting, and BlanketsTools

Insulated Tools, Hot Sticks, Static Discharge Sticks, Rescue Tools

ALWAYS Inspect Before Use and Maintain as Required

Keep the Tools and Equipment Clean

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Electrically Insulating GlovesGlove Classes by Use Voltage

Procure Through Your Local D/S ES&H Department

Use Leather Protectors with Gloves Gloves must be tested after every 6 months of use

through Fermilab’s program (April 1 and October 1 are Scheduled Exchange Dates)

Class 00 500 voltsClass 00 500 volts Class 0 1,000 voltsClass 0 1,000 volts

Class 1 7,500 voltsClass 1 7,500 volts Class 2 17,000 voltsClass 2 17,000 volts

Class 3 26,500 voltsClass 3 26,500 volts Class 4 36,000 voltsClass 4 36,000 volts

273

Over Voltage CategoryThe level and energy of voltage impulses or

surges is dependent on the location. The closer the location is to the power source, the higher the available fault current, the higher the category

IEC 61010 defines four locations or categories:CAT IV “Origin of installation”

Utility level and any outside cable run

CAT III Distribution wiring, including “mains” bus, feedersand branch circuits; permanently installed loads.

CAT II Receptacle outlet circuit; plug-in loads.

CAT I Protected electronic circuits

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CAT III-

600 V

CAT III-1000 V

CAT IV-600 V CAT III-

1000 V

Voltage Testing EquipmentMeters

Use Cat III Rated 600 or 1000 Volt for Indoor Work (Fluke T3 Tester is Stocked)

Use Cat IV for Outdoor WorkProximity – Inductive Voltage ProbesThe Wiggy – No Longer Acceptable

Test Before and After UseLOTO after use check

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Meter Safety ChecklistWatch for:Cracked or oily caseBroken input jacks

No Meter is Safe When Improperly

Used. Use meters within their rating.Use meters designed for measurements on

power circuits.Use replacement fuses approved by the

manufacturer278

Pertinent DefinitionsFlash Protection Boundary

Distance from an exposed live part within which a person could receive a 2o burn from an arc-flash

Incident energy necessary for a 2nd degree burn is 1.2 cal/cm2 with an exposure time of 1 second

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Pertinent Definitions

Arc Thermal Protection Value (ATPV) A rating associated with PPE such as face

shields, hoods, jackets, coats and coveralls that is expressed in cal/cm2

Flame-Resistant (FR)The property of a material whereby combustion

is prevented, terminated, or inhibited following the application of a flaming or non-flaming source of ignition, with or without subsequent removal of the ignition source

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1997 Arc-Flash Accident at F0 Compressor Room

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Fault Current and Duration Determine the Incident Energy of the

Arc-Flash

Fault CurrentShort Circuit or Bolted Fault CurrentAvailable Fault Current is Not Infinite

Limited by the Utility Generator, Transformers, Conductor Sizes and Length

Different Values within the CircuitTransformer Impedance (%IZ)

- Fundamental to the Value of the Short Circuit Current of a Transformer

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First Calculate the Transformer’s Full Load CurrentI FLA = (Transformer KVA Rating x1000)/

(Secondary Voltage Line to Line X 1.732)

2,000 KVA, 13.8KV to 480 VAC2,000 KVA, 13.8KV to 480 VAC 2,406 Amps2,406 Amps

1500 KVA, 13.8 KV to 480 VAC1500 KVA, 13.8 KV to 480 VAC 1,804 Amps1,804 Amps

750 KVA, 13.8 KV to 480 VAC750 KVA, 13.8 KV to 480 VAC 902 Amps902 Amps

500 KVA, 13.8 KV to 480 VAC500 KVA, 13.8 KV to 480 VAC 601 Amps601 Amps

75 KVA, 480 VAC to 120/208 VAC75 KVA, 480 VAC to 120/208 VAC 208 Amps208 Amps

45 KVA, 480 KVA to 120/208 VAC45 KVA, 480 KVA to 120/208 VAC 125 Amps 125 Amps

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Then Calculate the Short Circuit CurrentI SCA = (1FLA X 100) / (Transformer %IZ x 0.9)

2000 KVA 480 VAC Out with 5.8%IZ2000 KVA 480 VAC Out with 5.8%IZ 46,086 Amps46,086 Amps




75 KVA 120/208 VAC Out with 4.3%IZ75 KVA 120/208 VAC Out with 4.3%IZ 5,379 Amps5,379 Amps

45 KVA 120/208 VAC Out with 4.1%IZ45 KVA 120/208 VAC Out with 4.1%IZ 3,385 Amps3,385 Amps

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Typical Trip Curves

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Typical Trip TimesCircuit Breakers

0.1 second or 6 cycles typical. Varies by Manufacturer and Current. See Trip Curves.

Current Limiting FusesGenerally one-half of a line cycle. Classes RK1, J, T and L are best.

Yard Transformers: Consult with FESS (Joe Pathiyil) for specific

location trip times

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Other Factors to ConsiderConductor size also serves to limit the

available short circuit current due to the natural resistance of the wire

Short Circuit Currents for Utilization Equipment are Most Always Less than those of the Sourcing Panelboard

Exposure depends on distance to incident energy. 18 Inches is a typical value used.

“Open” or apply the “Box Factor”

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Flash Hazard AnalysisThe Flash HA determines the Flash Protection

Boundary and the protective clothing and PPE requiredRefer 130.3 on page 25

Requires knowledge of Fault current Duration of the fault currentLocation of potential arc-flash and Worker body position

290

Flash Protection BoundaryNFPA 70E 130.3 (A):

D FPB = (2.65 X MVA bf X t)1/2

Systems 600 volts or less default boundary 4’

2000 KVA with t = 0.12000 KVA with t = 0.1 2.4 Feet2.4 Feet





45 KVA with t = 0.0545 KVA with t = 0.05 0.3 feet0.3 feet

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Wear and Care of PPEWear CottonAvoid Scratching Eye ProtectionNo Bleach or Fabric SoftenersWear Clothing Loose, rather than Tight Layering Increases Protection Dry is Better than Wet

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Safe Work PracticesBe AlertUse Common SenseNo blind reaching. If view is obstructed, you

cannot work on live parts.Illumination must be providedConductive articles (jewelry, clothing) shall not

be worn

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Safe Work PracticesPlan for Emergencies

Know how to de-energize Quickly orBe prepared to pull employee free with an

Insulated Rescue HookHave the Means Available to Contact

Emergency Personnel - Dial 3131Know CPR & Where AED’s are located

Contact ESH Section for training

See FESHM 5048 for additional SWPs

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Verification of De-EnergizationMost Important Step in LOTOAssume Energized

PPE, Voltage Rated Tools and GlovesEstablish Appropriate Boundaries

Do not use Proximity Meters as your Primary Testing Tool (HV excepted)

Know your Test Equipment is WorkingTest Before and After Use

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THANK YOU

OPEN DISCUSSION

Electrical Safety Malagement

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