Electrical Failure Analysis for Fire and Incident Investigation

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Electrical

Failure Analysisfor fire & incident investigationswith over 400 illustrations

Dr. Marcus O. Durham, PE, CFEI, CVFI

Dr. Robert A. Durham, PE, CFEI, CVFI

Rosemary Durham, CFEI, CVFI

Jason Coffin, CFEI, CVFI

THEWAY Corp.

PO Box 33124

Tulsa, OK 74153

918-496-8709

www.ThewayCorp.com

Edition: 110511

Copyright 2009 - 2011 All rights reserved.
http://www.thewaycorp.com/http://www.thewaycorp.com/acehttp://www.thewaycorp.com/


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Electrical Failure Analysis

for fire & incident investigations

with over 400 illustrations

Contact:THEWAY Corp.P.O. Box 33124

Tulsa, OK 74153918-496-8709

[email protected]

Editor: Marcus O. Durham

Cover Design: Marcus O. DurhamPrinted in United States of America

First printing by Dream Point Publishers, September 2010

Library of Congress Control Number

ISBN:

Copyright 2009 - 2011 by Marcus O. Durham, Theway Corp.

All rights reserved under International Copyright Law. Contents and/or cover may not be

reproduced in whole or in part in any form without the express written consent of the

Publisher.
http://www.thewaycorp.com/mailto:[email protected]://www.thewaycorp.com/acemailto:[email protected]://www.thewaycorp.com/


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TABLE OFCONTENTS

Table of Contents ................................................................................................. 3Preface .................................................................................................................. 9

0.1 Overview ................................................................................................ 9Chapter 1 - Fundamentals ................................................................................... 11

1.1 Introduction .......................................................................................... 111.2 Its All About 3s ................................................................................. 121.3 Measure ................................................................................................ 121.4 Calculate .............................................................................................. 121.5 Impedance ............................................................................................ 131.6 Recap ................................................................................................... 131.7 Wire purpose ........................................................................................ 141.8 Source of power ................................................................................... 141.9 Nominal voltages ................................................................................. 151.10 Conductors ...................................................................................... 151.11 Review ............................................................................................ 16

InterludeAnalysis Team ................................................................................. 17

Chapter 2 - How it failsResult of Failure ....................................................... 192.1 Introduction .......................................................................................... 192.2 Metals ................................................................................................... 192.3 Electrical metal conditions ................................................................... 202.4 Failures ................................................................................................. 202.5 Sources of ignition ............................................................................... 212.6 Non-contact ignition ............................................................................ 222.7 An Illustration ...................................................................................... 222.8 Debunking arc-mapping myths ............................................................ 232.9 Fault Forms .......................................................................................... 242.10 Heat transfer .................................................................................... 242.11 Temperature and power ................................................................... 252.12 Fire .................................................................................................. 25

2.13 Review ............................................................................................ 252.14 BibliographyIllustrations ............................................................. 26

Chapter 3Why it Fails - Cause of Failure ....................................................... 273.1 Introduction .......................................................................................... 273.2 Why? Cause of failure .......................................................................... 273.3 Process ................................................................................................. 283.4 Physics ................................................................................................. 283.5 Components of system ......................................................................... 293.6 Missteps ............................................................................................... 303.7 Deterioration ........................................................................................ 303.8 Probability factors ................................................................................ 303.9 Outside influence ................................................................................. 313.10 Electrical measure ........................................................................... 31

3.11 Review ............................................................................................ 323.12 Bibliography - Illustrations ............................................................. 33

Chapter 4Heating Devices .............................................................................. 354.1 Introduction .......................................................................................... 354.2 Thermal cut-offs ................................................................................... 354.3 Fixed .................................................................................................... 36

4.3.1 Source ......................................................................................... 364.3.2 Path ............................................................................................. 364.3.3 HVAC heaters ............................................................................ 374.3.4 Cooktop & Ovens ....................................................................... 374.3.5 Clothes dryers ............................................................................. 384.3.6 Recessed lights ........................................................................... 384.3.7 Fluorescent lights........................................................................ 39


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4 Electrical Failure Analysis Durham

4.3.8 Enclosed lights ........................................................................... 394.4 Portable ................................................................................................ 40

4.4.1 Source & Path ............................................................................ 404.4.2 Ceramic and other heaters .......................................................... 404.4.3 Lamps ........................................................................................ 404.4.4 Kitchen appliances ..................................................................... 414.4.5 Microwave ................................................................................. 414.4.6 Office appliances ....................................................................... 41

4.5 Handy .................................................................................................. 414.5.1 Source & Path ............................................................................ 414.5.2 Hair dryers ................................................................................. 424.5.3 Hair irons ................................................................................... 424.5.4 Clothes irons .............................................................................. 424.5.5 Tools .......................................................................................... 424.5.6 Battery chargers ......................................................................... 43

4.6 Review ................................................................................................. 43Chapter 5Cooling & Other Devices ............................................................... 47

5.1 Introduction ......................................................................................... 475.2 Common risks...................................................................................... 475.3 Cooling ................................................................................................ 485.4 Fan ....................................................................................................... 48

5.5 Water ................................................................................................... 495.6 Class 2 power supplies ........................................................................ 495.7 Electronics ........................................................................................... 505.8 Review ................................................................................................. 50

Chapter 6Protection ....................................................................................... 536.1 Introduction ......................................................................................... 536.2 Current ................................................................................................. 536.3 Voltage ................................................................................................ 536.4 GFCI .................................................................................................... 546.5 AFCI .................................................................................................... 546.6 Surge Protection Systems .................................................................... 546.7 True UPS ............................................................................................. 556.8 Battery Back-up UPS .......................................................................... 55

6.9 Surge suppressors ................................................................................ 556.10 Power strips .................................................................................... 566.11 Protected power strips ..................................................................... 566.12 Caveats - U/L .................................................................................. 566.13 Extension cords............................................................................... 566.14 Review ............................................................................................ 56

Chapter 7Grounding ...................................................................................... 597.1 Introduction ......................................................................................... 597.2 Investigator perspective ....................................................................... 597.3 3-in-1 ................................................................................................... 607.4 Grounding system ................................................................................ 607.5 Neutral ................................................................................................. 617.6 Stray .................................................................................................... 617.7 Stray 120/240V .................................................................................... 617.8 Ground differences .............................................................................. 627.9 Grounding electrode ............................................................................ 627.10 Ground values ................................................................................. 627.11 Illustrationcirculating current ..................................................... 637.12 How much is too much? ................................................................. 647.13 Measurement .................................................................................. 647.14 Grounding & lightning ................................................................... 657.15 Sum it up ......................................................................................... 657.16 Review ............................................................................................ 657.17 Bibliography - Illustrations ............................................................ 66

Chapter 8Codes & Law.................................................................................. 678.1 Introduction ......................................................................................... 67


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Table of Contents 5

8.2 National Electrical Code ...................................................................... 678.3 Jurisdiction ........................................................................................... 688.4 National Electrical Safety Code ........................................................... 688.5 State Law ............................................................................................. 698.6 Importance ........................................................................................... 698.7 IEEE 142 .............................................................................................. 698.8 NFPA 780 ............................................................................................ 708.9 NFPA 921 ............................................................................................ 708.10 Professional responsibility .............................................................. 718.11 Review ............................................................................................ 71

Chapter 9Electric and Communication Utilities ............................................. 739.1 Introduction .......................................................................................... 739.2 Electric utility ....................................................................................... 739.3 Communications .................................................................................. 749.4 Radio & Television .............................................................................. 749.5 CATV ................................................................................................... 759.6 Network powered broadband ............................................................... 759.7 Intersystem Bonding ............................................................................ 769.8 Review ................................................................................................. 77

Chapter 10Lightning....................................................................................... 7910.1 Introduction ..................................................................................... 79

10.2 Differential potential ....................................................................... 7910.3 Lightning transients ......................................................................... 7910.4 Strokes ............................................................................................. 8010.5 Control ............................................................................................ 8010.6 Ground ............................................................................................ 8110.7 Bond ................................................................................................ 8110.8 Errors & omissions .......................................................................... 81

10.8.1 Clear air and end poles........................................................... 8110.8.2 Poor ground electrode ............................................................ 8210.8.3 Rebar ...................................................................................... 8210.8.4 Gas pipe ................................................................................. 8210.8.5 Satellite dish & cable ............................................................. 82

10.9 Grounding & lightning .................................................................... 83

10.1 lightning Report .............................................................................. 83Chapter 11Artifact identification .................................................................... 8511.1 Introduction ..................................................................................... 8511.2 First ................................................................................................. 8511.3 Sleuth .............................................................................................. 8511.4 Corporate memory........................................................................... 8611.5 Legwork .......................................................................................... 8611.6 Exemplar ......................................................................................... 8611.7 Team ................................................................................................ 86

Chapter 12User Warnings .............................................................................. 8712.1 Introduction ..................................................................................... 8712.2 Warnings ......................................................................................... 87

Chapter 13Safety ............................................................................................ 8913.1 Introduction ..................................................................................... 8913.2 Personal Protection Equipment ....................................................... 8913.3 Scene evaluation .............................................................................. 9013.4 Lockout / tagout .............................................................................. 90

Chapter 14Ethics ............................................................................................ 9114.1 Introduction ..................................................................................... 9114.2 Morality ........................................................................................... 9114.3 Ethics vs law ................................................................................... 9214.4 Client ............................................................................................... 9314.5 Predilection ..................................................................................... 9414.6 Support ............................................................................................ 9414.7 Public and private ............................................................................ 95


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14.8 Rules ............................................................................................... 9514.9 Resolution ....................................................................................... 9614.10 Authors ........................................................................................... 9614.11 Bibliographyillustrations ............................................................ 96

Chapter 15Practices & Procedures ................................................................. 9715.1 Introduction .................................................................................... 9715.2 Economics ...................................................................................... 9715.3 Scientific method ............................................................................ 9815.4 Fire departments ............................................................................. 9815.5 Initial identifier ............................................................................... 9915.6 Origin & cause .............................................................................. 10015.7 Engineers ...................................................................................... 10015.8 The rest of the story ...................................................................... 101

Chapter 16Water Impact .............................................................................. 10316.1 Introduction .................................................................................. 10316.2 3-in-1 failure modes ...................................................................... 10316.3 Conducting.................................................................................... 10316.4 Corrosion ...................................................................................... 10316.5 Deposition ..................................................................................... 10316.6 Manifestation ................................................................................ 10416.7 Migration ...................................................................................... 104

16.8 Mitigation ..................................................................................... 10516.9 Machination .................................................................................. 10516.10 Review .......................................................................................... 105

Chapter 17Petrochemicals ........................................................................... 10717.1 Introduction .................................................................................. 10717.1 Units ............................................................................................. 10717.2 Properties ...................................................................................... 10717.3 Conversions .................................................................................. 10817.4 UL flammability rating ................................................................. 10817.5 Electrical fault and flammability .................................................. 10917.6 Heat release rate ............................................................................ 10917.7 Codes ............................................................................................ 11017.8 National Fuel Gas Code ................................................................ 111

17.9 Regulations ................................................................................... 11117.10 Analysis ........................................................................................ 112Chapter 18Energy Analysis - Fire Movement and Energy Transport .......... 113

18.1 Introduction .................................................................................. 11318.2 Energy........................................................................................... 11318.3 Units ............................................................................................. 11418.4 Its All About 3s .......................................................................... 11418.5 Distance sidebar ............................................................................ 11418.6 Energy - Measure .......................................................................... 11518.7 Energy - Calculate ........................................................................ 11518.8 Energy - Review ........................................................................... 11518.9 Transport - Measure ...................................................................... 11618.10 Transport - Calculate .................................................................... 11618.11 Transport - Impedance .................................................................. 11718.12 Transport - Review ....................................................................... 11718.1 Temperature .................................................................................. 11818.2 Ignition temperatures .................................................................... 11918.3 Plumes .......................................................................................... 11918.4 A thing called entropy .................................................................. 11918.5 Realms of energy .......................................................................... 12018.6 Review .......................................................................................... 120

Chapter 19Biological Effects ........................................................................ 12319.1 Introduction .................................................................................. 12319.2 Routes ........................................................................................... 12319.3 Electrical / Biological Research .................................................... 12319.4 Some Players ................................................................................ 124


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Table of Contents 7

19.5 Effect of Shock .............................................................................. 12419.6 Its Threes...................................................................................... 12519.7 Whats the Difference?.................................................................. 12519.8 Code Basis? ................................................................................... 12619.9 Stray Current ................................................................................. 12719.10 Electromagnetic Energy ................................................................ 12719.11 Summary - Its Just Physics .......................................................... 12819.12 Bibliography - Illustrations .......................................................... 128

Chapter 20Projects ....................................................................................... 12920.1 Introduction ................................................................................... 129

Chapter 21Plateselectrical failure photos .................................................. 13121.1 Introduction ................................................................................... 131

Authors ............................................................................................................. 145Dr. Marcus O. Durham, PE, CFEI, CVFI .................................................... 145Dr. Robert A. Durham, PE, CFEI, CVFI ..................................................... 145Rosemary Durham, CFEI, CVFI ................................................................. 146Jason A. Coffin, CFEI, CVFI ...................................................................... 147

Supplemental .................................................................................................... 14922.1 Electrical Failure Questionsinitial ........................................... 14922.2 Electrical Failure Questionsfollow-up ..................................... 15022.3 Electrical Shock Survey ................................................................ 151

22.4 Evaluation Form - electrical failure analysis ................................. 153finis ................................................................................................................... 155


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PREFACE

0.1 OVERVIEWThe book is structured for anyone working in the failure analysis industry. The course is particularlydesigned for individuals that encounter electrical systems in the process of incident investigations. Thisincludes engineers, technicians, investigators, insurance, legal, supervisors, and staff. There is enoughtechnical information that any investigator will benefit from the material, illustrations, and explanations.

The book is not intended to make the user an electrical expert, but to broaden the investigators insight intoelectrical systems.

There are over 400 illustarations. The majority are photos of actual incidents we have investigated. Otherphotos are of events we have created in our research and are used as illustrations and aids. There arenumerous diagrams to document the discussion.

The book has purposefully limited the use of equations and math to make it more accessible. That does not

limit the technical value and discussion. Only one chapter on Energy Transport is heavily structured withmath to illustrate the thermodynamic engineering principles. That material can be bypassed by non-engineers.

At the completion of the book and short course, the participant will understand the components of and knowhow to look at failures, particularly as related to electrical. This investigation will involve considerations ofthe Codes and Standards. As members of several Standards organizations, we can assure you that issuesaddressed in these references are only there because someone had a problem. The discussion will furtherinvolve the relationship between investigators, engineers, and legal, as well as the role of public and privatesector processes.

In addition to a book structured for electrical failures, there are hands-on components and illustrations. Thereare numerous plates of electrical failures that we have created in our research. The creation assures the

analysis and description is appropriate.A field exercise will be conducted to see actual equipment and failures. There will be problem solvingindividually and with a team.

The book has hundreds of color photographs. However, printing cost of color is expensive.

Bring your computer. The entire book, in color, can be downloaded for personal access during discussions.

Enjoy and good learning!


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$universal engineering symbol

$, t, qualityengineering trade-offs

CHAPTER 1-FUNDAMENTALS

1.1 INTRODUCTIONElectrical power is the primary form of energy in residences andbusiness. It is commonly used, but its functions are seldom considered.Electrical systems receive very little attention in proportion to their

impact; moreover, most operations are critically dependent on electricalenergy. Whether for lighting, heating, motors, computers orenvironmental systems, electricity has become the most used and flexibleenergy form.

The major reasons that study of electrical system is shunned are threefold. The first reason is fear of the perceived hazards associated withelectricity. The second obstacle is a lack of understanding of thefundamental theory. The third hurdle is the fact that electrical conceptsmust be explained by nebulous models. Electricity defies the normalsenses. One cannot see, hear, taste, smell, or touch electricity withoutsignificant hazard.

A good grasp and working knowledge of the electrical fundamentals can,nevertheless, be obtained without being a graduate electrical engineer.This book is presented in a form designed to assist future quickreference, as well as to provide a background for understanding electricalphenomena.

Electricity is a convenient form to transfer energy. Seldom is electricalenergy generated and used directly. On the contrary, electrical systemsconvert an available energy source such as gas, coal, hydro, nuclear,wind, or solar to electrical energy. The generated electricity is thenconveniently transferred to a load center. The devices at the load centerconvert the electrical energy back to another useful energy form such aslight, heat, or mechanical motion.

A generic electrical system covers equipment from a generator or powersupply through controls to a motor or load.

GENERATOR MOTORCONTROLLERTRANSFORMER METER

This book does not specifically address the transmission and distributionof electrically energy. Rather, the concepts covered are applied to the topof the power pole to the bottom of the basement. Since every electricalpower circuit has the same form, the concepts discussed are applicable to

any situation where electric energy is used. The items of discussion willbe basic terminology, application, and failure considerations.

In addition to technology, the design and installation of any electricalsystem must consider three major items - safety, environment, and cost.In the design, manufacture, and installation of any item there are trade-offs to achieve a particular dollar, time, or quality value. Failures, then,are a result of poor quality, misuse, or abuse of the product.

Understanding electricity

3-D: a triad example

Hear no evil, See no evil, Speak no evil


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1.2 ITSALLABOUT3SElectrical systems, as all physical systems, operate based on the Trinityor Triad Principle [1] which states:

Any item than can be uniquely identified can be further

explained by three components.

The necessary terms for an electrical system can be identified using thisgrouping of three quantities. If a discussion of a system has either moreor fewer items, it is either a combination of unique terms, or aninadequately explained or inadequately defined system.

1.3 MEASUREOnly three items can be measured in any energy system. All othercomponents are calculated from these. The measured components are

pressure (potential), flow (transfer rate), and time.

It follows, then, that only three items can be measured in an electricalenergy system.

Voltage (V) - measured as Volts - is the potential force or pressure in acircuit. It exists whether anything is connected or not. Voltage ismeasured across, or as the difference between, two points. Voltage issimilar to pounds per square inch (psi) on a water line.

Current (I) - measured as Amps - is the rate or quantity of flow through apath. Current can be measured only if a load or fault is connected andoperating. The measure for current is an Amp, which is a quantity ofelectrons per second. Current is similar to gallons per minute on a waterline.

Time event (t) - measured in seconds - is the elapsed time betweenevents. The reciprocal of time is the frequency (f), whici is measured inoscillations per second.

The three measurements combine in one term to produce energy (W).

Energy is the work or activity performed due to force. It is the commonmeasure between electrical, mechanical, and chemical systems.

1.4 CALCULATEFrom these three measured variables, three things can be calculated. Allelectrical relationships can be derived from the three measured terms -voltage current, and time. Since the terms are unlike, you cannot add or

subtract. The only thing left to do, then, is to multiply and divide.

Power (S) - expressed in Volt-Amps - is the product of voltage andcurrent. Power is energy or work that occurs over some period of time.The asterisk simply notes a time change on the current.

Impedance (Z) - expressed in Ohms - is the ratio of voltage to current(Volts per Amp). Impedance is the opposition to current flow. Therelationship is called Ohms Law.

Parameter Symbol Units What

Voltage V Volts potential

Current I Amps flow rate

Time t seconds duration

Impedance

divide

Flow rate is like current

Powermultiply

Pressure is like voltage

3 measures in 1 term3in


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Chapter 1 Fundamentals 13

Delay (td) - is the difference is the time between voltage and current. Itmay be expressed in seconds or in angular terms. It is the phase shiftbetween voltage being at a maximum and current being at a maximum.In power systems it is called power factor. It is the differential that arisesin the Calculus.

EXAMPLES

Ex1.4-1

Given: 120 Volts and 10 Amps.What is the impedance?

Ex1.4-2

Given: 120 Volts and 10 Amps.What is the power?

1.5 IMPEDANCEThe opposition to current flow is called impedance. Impedance is aconsequence of how electrical conductors are configured. As would beexpected, there are three types of opposition.

Resistance (R) is natural opposition of any conductor. Most conductorsare wires made of copper or aluminum. Resistance is the friction of aconductor. A resistorconverts electrical energy into mechanical energyin the form of heat.

Inductance (L) results from a conductor being bent into a coil. A coilconverts electrical energy into a magnet. A coil stores magnetic energy.Coils are used to make relays, motors, and transformers.

Capacitance (C) results from two conductors being close to each other.A capacitorstores electrical energy. A capacitor can be used to smoothout the electrical energy. Capacitors are used in electronic circuits and toreduce the effect of time delay from a coil. In power circuits, capacitorsare often used to assist with motor starting.

For each type of impedance, there is corresponding power consumption.These three combine to create the product Volt-Amp. The most familiarof the three is resistance which creates heat and the resulting power isWatts.

1.6 RECAPTake a minute to review all the electrical terms. Remember they arealways in groups of three.

There are three things that can be measuredvoltage (pressure), current(flow rate), and time.

There are three things that can be calculated the ratio calledimpedance, the product called power, and the time delay.

Finally there are three types of impedance or opposition resistancemakes heat, coils make magnets, and capacitors store and smoothelectricity.

Parameter Symbol Units What

Impedance Z Ohms () ratio

Power S VoltAmps product

Delay td or seconds differenc

Impedance Z Energy

Resistance R mechanicalInductance L magnetic

Capacitance C electric

Wire corresponds to pipe

Resistor

That is all there is

Capacitor

Dielectric

Between plates

Plates

are Al foi

Outer cover is

plastic or metal

Alternating plates

connect to terminals

Inductorcoil of wir


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That is all there is. There is nothing else in the fundamentals ofelectricity.

1.7 WIRE PURPOSEElectricity operates in a circuit. The energy starts at a point, travelsthrough wires to a load that does some work, then returns back to the

starting point. Wires have one of three purposes in the circuit.Hot conductor carries the current to do the work. When looking at astandard receptacle, this is the short prong. It is the black wire and isconnected to the brass color terminal.

Neutralconductor is the return or common conductor that completes thecurrent path back to the source. This is the wide prong on a 120Vreceptacle. It is the white wire and is connected to the silver colorterminal. It is carrying current, but, under ideal circumstances, thevoltage measured to ground is zero.

Ground conductor is the safety path. It does not carry current duringnormal operations, but is a path for when things go wrong. This is the

round prong. It is the green or bare wire and is connected to the greencolor terminal. All metal associated with the electrical system should bebonded to the ground in a specified manner.

The neutral is connected to the ground system at one point, and one pointonly. This is typically in the main circuit breaker panel. If there is a paneland a sub-panel, the neutral in the second panel is not connected toground. Doing so would make an energized path for current through theground wiring.

The wires are typically grouped together in a cable. Permanentlyinstalled cable in a residence is often NM, or non-metallic sheath, cable.In common usage it may be referred to as Romex, which is one brand.

Appliance and extension cords may not have a ground conductor if thereis no risk of a user touching metal that can be energized. Theseappliances are often referred to as double insulated.

1.8 SOURCE OF POWERAll common electrical power is carried in conductors or wires. Thearrangement of these wires determines the wire function. There are threefundamental power supplies.

Direct currentis generally associated with batteries. It delivers a steady,constant voltage. The color scheme used is a red wire for positive and ablack wire for the negative.

Single-phase (1) is an electrical system that uses only two currentcarrying conductors. The supply is generally derived from a rotatingmachine that causes a cyclic voltage variation. The color scheme used isblack for the hot side and white, or grey, for the neutral or common. Theground wire is identified with green. This is the most common typeelectrical system in residences and commercial installations.

Three-phase (3) is a system that uses three current carrying conductors.The system is actually three single-phase systems connected together.The color scheme uses any color for the current carrying conductors,although black is the most common. The ground wire is still identified bygreen.

DCmobile battery

Standard 120, 15A receptacle

120 / 240 V receptacle

H1 H2N G

120 V 120 V

240 V

Standard 120 / 240 V single-phase


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Chapter 1 Fundamentals 15

1.9 NOMINAL VOLTAGESThere are many different system voltage levels. For failure analysis thesecan be separated into three categories non-lethal, standard, and highenergy.

Non-lethalis electrical supplies less than 50 volts. Electronics, portable,and mobile items are typically low voltage items. Common voltages are

3, 5, 9, 12, and 24 volts. Electric welders also operate in this voltagerange. Although in a non-lethal system, the voltage is low and will notfatally injure someone, clearly the power systems can still have adequateenergy to cause a fire, or to cause some injury.

Standardpower voltages are typically 120 and 240 Volts, single-phase.This is by far the most common system. They predominate in bothresidences and commercial installations. A 240 Volt source has two hotconductors. A 120 Volt source uses one of the hot connectors and aneutral. A 240 Volt source is actually two 120 Volt sources with theneutral as the common connection. Because 120/240 Volt systems are soprevalent, they are a frequent source of injury and fire. Theseinstallations are covered by theNational Electrical Code.

Large energy voltages are anything higher than 240V. Large motors andloads operate at 277 Volts to 7,200 Volts, while utility lines operatebetween 12,470 Volts and 1,000,000 Volts. Obviously, these arepotentially very dangerous to both people and property. However,because they are usually used only by authorized and trained individuals,failure is not as common as standardpower systems. Inside facilities,these installations are covered by theNational Electric Code. Utility typesystems are covered by theNational Electrical Safety Code.

1.10 CONDUCTORSPaths for electricity can consist of simple metal, insulated metal, or agroup of paths.

Conductors are metal material that is used for an electrical path. Themost common metal used for conductors in residential and commercialinstallations is copper. Aluminum is used outside of buildings and forlarge feeders in buildings. Gold and silver are used in electronics.

Wire consists of a conductor covered with insulation. The componentscan be compared to the water circuit discussed earlier. The size ordiameter of the conductor (pipe) determines how much current cansafely flow. The thickness and type of insulation is like wall thickness ofpipe and determines the voltage (pressure) rating. The length of the wire(pipe) causes a voltage or pressure reduction at the end.

Cable is simply more than one wire that is bundled together. It has anouter covering called a jacket.

DCportable battery

Three-phase large power

Three-phase pole top

Welderlow voltage but high current


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1.11REVIEWElectrical fundamentals always exist in groups of three.

Measuredvalues are

voltage

current time

Calculated values are

Impedance (ratio) Power (product) Shift (time difference)

Impedance components are

resistance inductance capacitance

Purpose of a wire is

hot neutral ground

Source of power is

direct current single-phase three-phase

Nominal voltage ranges are

non-lethal standard large-energy

Conductors are used as

single conductor wire cable

CablesNM 12, NM 14, UF , UF w/ gnd

Wirestranded, solid

Ground Al #2 strand

Hot Al #2 strand

Neutral

Neutral

Ground


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INTERLUDEANALYSISTEAMAfter the electrical concepts and before failure analysis, it is worthwhileto consider how we get there. It is a team effort.

Fire investigators look to where the fire originates the area of originand what was the sourcecause of ignition. Equipment systems that canfail are electrical, mechanical, or chemical.

Engineers look at the systems to determine how the failure occurred andwhy. The next chapter will look at how electrical systems fail. Then wewill look at why or the causes of failure. Engineers look at themechanism of the failure.

Subsequent chapters will look at specifics of particular equipment andsystems.

An alternative terminology provides differentiation in the scale of theinvestigation. Investigators look at the large scale macro. Engineerslook at the detailsmicro.

INVESTIGATOR ENGINEERcause of fire cause of failure

where - origin how system failed

ignition sourceelectrical, mechanical, chemical

why system failed

macro micro

knowledge of fire knowledge of systems

CodesNFPA 921 CodesNEC, NESC, IEEE

A later chapter will discuss the details of the investigation process.


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CHAPTER 2-HOW IT FAILS

RESULT OFFAILURE

2.1 INTRODUCTIONThe investigator determines the area of the origin of the fire and what

caused thefire. The cause may be electrical, mechanical, or chemical.

The engineer determines the cause of thefailure of equipment, if there isa defect, and why the equipment failed. Sometimes there is an overlap ondetermination ofwhatcaused the fire.

These chapters give insight into why things fail so there can be greaterunderstanding as to what caused the fire. The first part is the way thingsfail. The next section is why things fail.

The discussion will not get into identifying specifics, since that is a verydetailed process. Similarly, it will not get into the codes, standards, andregulations.

Electrical activity is a common term for investigators to use whenreferring to failures that are associated with electrical systems. The termis generic and may refer to either a cause or result.

The presence of electrical activity implies that there is need for furtherinvestigation to ascertain whether the electrical system was an issue inthe event and to ascertain why the activity was precipitated.

2.2 METALSMetals are a key item to investigate a fire. They tend to survive in somecondition. Furthermore they hold and show the heat patterns.

Steel and stainless steel are iron-based (ferrous) materials. Iron is notoften used for an electrical conductor, but is used for enclosures. Steel isused in the core of motors and transformers. Ferrous materials are anadequate conductor that may contribute to an electrical related failure.Appliances and some tools have these materials. Structural members alsohave ferrous materials. Steels melt about 2600F or higher; they survivemost incidents. Mechanical strength, however, may be lost at muchlower temperatures, resulting in structural failure.

Copper is the predominant electrical material. It has a meltingtemperature of about 1980F. It survives most fires in some form and is aprimary indicator of electrical involvement in the fire.

Aluminum is the second most used electrical wire. Aluminum meltsabout 1220F. It seldom survives a fire, but that fact can be used inanalysis. Aluminum has several installation issues and the connectionscan cause a fire. Copper should not be connected to aluminum since apoor connection will result and can cause a fire. Special provisions mustbe made when this type of connection is necessary.

The temperature values described are typical. Different alloys will haveother properties.

Metal F C

Steel 2600 1427

Copper 1981 1082

Aluminum 1220 660

Investigatorsdetermine cause offire -whatis source of ignition

Engineersdetermine cause offailure -how equipment failswhy equipment failed

Energized - generative

If you cannot fix it with a hammer,

you have an electrical problem.-wry philosophy


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2.3 ELECTRICAL METAL CONDITIONSMetals are clearly associated with fire both as a contributing cause and asan indicator. How the conductor was used at the time of the incident willdetermine the pattern or indication of failure. The three conditions forelectrical fire relation are energized generative, energized result, and de-energized. The illustrative photos are from actual incidents we have

investigated.Energized generative includes electrical items that are the reason for thefailure or fire. There are indicators that a wire is energized. Similarlythere are patterns and results that show a wire or conductor may be thecause of the event. These are complex and must be evaluated in thecontext of all the other events, patterns, and information associated withthe incident.

When the components are the cause of the fire, they are often

destroyed by the intense energy at the location of the incident. Therefore, there is very little published information and illustrationsabout the damaged items; however, adjacent parts may survive in someform. Identification comes about by the process of elimination. This isthe part of the scientific method of gathering data, developing hypothesisand testing the hypothesis.

The most common indication is a divot in the metal conductor. Theremay be a corresponding bead where metal was deposited. If componentsare found that are the cause they will have this form. However, this

form may exist and not be the cause.

Energized resultincludes electrical items that are energized at the time ofthe fire, but the damage is due to encroaching heat from the incident.There are resulting indicators that illustrate the wire was energized, butdid not fail and cause the event. The most common indication is a beadof metal conductor with a clear line of demarcation.

Non-energized items cannot be an electrical cause of the failure orincident since there is no electrical energy. Nevertheless, the componentsare metal and will have distinctive patterns and can be used as anindicator for direction of progression and location of other sources. Themost common indication is simply melting and flowing of the metal.

Balls may be similar to beads, but witout the clear demarcation. Ballswill tend to have bubbles from popping gas and impurities in the metal.Metal may be lost from pitting, but it will lack a clear divot.

Each of the conditionsenergized generative, energized result, and non-energizedhas characteristics and patterns to assist with the analysis. A

major part of the process is elimination of other potential sources.

2.4 FAILURESFailures of electrical systems and components are directly related to thethree items that can be measured. Each of the three causes a unique typeof failure. There are three ways an electrical system fails insulationloss, connections, and transients.

Insulation loss causes a voltage breakdown failure. The loss of insulationallows current to take a path other than the preferred path down the wire.The resulting current can create heat.

Energized - result

Non-energized

Insulation loss mechanical damage

Connection loose circuit breaker


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Chapter 2 How It Fails 21

Loss of insulation can result from mechanical damage, inadequatematerial during manufacture, and electrical stress from over-voltage.

Connections that are inadequate cause a current type failure. A poorconnection causes a heat build-up which can ignite surroundingmaterials. Contaminants such as moisture can begin oxidization whichincreases the resistance of the connection. Oxidation products can makethe connection appear to be tight.

Three common situations create inadequate connections. (1) Switchcontacts can be misaligned, pitted, or too small. (2) Contaminants such aswater, carbon, and debris can create an unintended path that will get hot.Debris may include damaged insulation. (3) Connectors that are loose getvery hot.

Warning: We have created fire with a connection that had a resistance aslow as only 0.25 Ohms. That is very close to a solid connection.

Transients or surges are time-related, very fast noise that gets injectedonto the power system. Transients overload the system, cause localizedheat, and can cause damage to the insulation.

Transients can be caused by switches, lightning, or intermittentconnections. These are perhaps the most difficult to recognize since thesituation may not exist for a long period of time and likely is notrepeatable. Nevertheless, transients are extremely common events thatoccur every time any electrical item is energized.

2.5 SOURCES OF IGNITIONSources of ignition from electrical systems can be either from contactwith energized metal or non-contact due to radiation. Contact ignitionhas three formsconnections,sparks, and arcs.

Connections cause power type heating. This is also called 2I Rheat

failure because the power is equal to the square of the current (current xcurrent) times the resistance. It is also called a high impedance failurebecause the impedance is greater than preferred.

The heat generated by this type failure increases with time, current, andthe resistance. In this arrangement the temperature of the connectionsimply increases over time. As heat increases, the impedance of theconnection can also increase, causing additional heat generation.Temperatures can easily exceed the ignition temperature of mostcombustibles. This is by far the most common cause of electricalignition. Although it is not as dramatic as others such as an arc.

Sparks are the heated and luminous metal particles that are ejectedthrough an insulating material such as air or wire insulation. Since theseare projectiles, they can traverse a varied path. The particle will be wellabove the melting temperature of the metal. Although possible, sparksare an uncommon cause because of low power density and rapid cooling.

Arcs are a short circuit through an insulation material, including air. Anarc-flash can create temperature in excess of 35,000F, a brilliant flashof light. An arc-blast, which is the result of the arc, can also create apressure wave that can cause materials to fly and a loud noise. Copperexpands 67,000 times during a conversion to vapor and shrapnel cantravel at 1600 km/hr (700 mph).

Connection heating*

Spark particles flying

Transient noise L-N

Arc flash50A, 250V, 14AWG


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An arc at 240 V is equivalent to 2.4 MW or approximately 2.4 sticks ofdynamite. Incidentally, this is also the heat released from a polyurethanesofa.

2.6 NON-CONTACT IGNITIONNon-contact ignition requires a separate analysis and has unique

properties.Radiation takes many forms but all are electromagnetic in nature.Radiation is derived from radar and microwaves as well as other highfrequency radio transmitters. Radiation heats the molecules of matterthrough a medium such as air, without significantly affecting the air.

Microwave ovens typically are heating water molecules. However, metalwithin the field will cause a disturbance and create extreme heatequivalent to a smelter. Note the microwave oven containing brick that isprotecting the metal can.

Ignition of most materials will occur if not protected from heat.

In addition,

2

I R heating can create enough heat energy to ignitematerials that are not in direct contact with the conductor. This is a formofconvective heating.

2.7 ANILLUSTRATIONAn electric arc-welder and mig-welder are excellent examples of anenergized conductor and the various ways that a fire may be the cause orthe result. The advantages of using a welder over other illustrations arereduced effects of char, the controllable current, and repeatable results.

All three contact ignition conditions exist connection,sparks, and arc.Sparks do occur, and can ignite combustible materials if they are in the

vicinity of a hot spark. By definition an arc is occurring, but there is nottypically ignitable material in the area. The high current and contact

between the electrode and the metal cause substantial 2I R heat.

All three metal conditions exist energized cause, energized result, and

de-energized.

Like all other ignitions sources, the electrical activity is complex andmust be evaluated in the context of all the other events, patterns, andinformation associated with the incident.

Where the energized electrode strikes the grounded metal, the electrodemetal is completely obliterated. There is no evidence of an electroderemaining. Therefore, it is not possible to say where the incident started

on the electrode. Nevertheless, there are indications of the remainingitems that do show involvement.

An energizedconductor will have a divot or cup at the place where metalwas transferred. This is sometimes called a parting arc, which isredundant. By definition, all arcs are the result of parting contact points.

Note the illustration for a welding electrode as well as the otherphotographs of actual incidents.

An energized resultwill have a rounded bead or ball associated with thecooling. The two conductors may be welded together. There will be adistinct line of demarcation at the bead.

Non-energized result of heating*

Radiation heating in microwave*

electrode

arcweld pool

weld metalbase metal

Arc metal transfer divot

Electric weldingarc, spark, heat*

Energized cause, result, nonenergized*


23/155


The result of a short circuit on stranded wire shows up as beading onindividual conductors. This is the result of heating on the individualwires, rather than ambient heating.

A non-energized result of heating will have characteristic pock marks,splatter, and the metal will not flow and join into a weld. The metal mayalso have indications of stretching.

Once a conductor is severed, current ceases to flow in the separatedcomponent. That conductor is de-energized and no further electricalactivity is possible; however, the energized electrode can continue tohave further cause or results. Therefore, it is necessary to track theconductor to the fault farthest from the source to find the initial incident.Remember, just because an electrical conductor is energized and faultsdoes not mean it is the cause of the incident.

2.8 DEBUNKING ARC-MAPPING MYTHSQuestion: If a fault occurs in the breaker panel, can there be later faultingat a location downstream of the panel?

There is a significant issue to consider when looking at arcing. On astandard 120/240 Volt power supply, there are two sources. Each hot lineor leg is separately energized. Therefore, one leg can be de-energizedwhile the other continues to supply power and can be a cause of failurethat is farther from the source.

Question: Is the most electrical activity in the area of origin?

Some investigators less familiar with the underlying electrical principlesattempt to look at all the arcing in an area. They assume the area of mostarcing is in the area of orign.

Au contraire. A fault may occur on a single conductor and trip the supplyon that line. Other breakers are still energized and may display activity

later in the incident.

Warning: Arc-mapping only shows information about activity on a

single conductor. Arc-mapping can only validly be used to show the

farthest point on a particular circuit.

Arc mapping is another of those ideas that many in the industry havetaken as gospel, based on a fragment of science, that has later beenproven to be unscientific. We have seen very bad decisions about origins,based on mis-application of this concept. Unfortunately, arson has beenadvocated when there was a simple electrical explanation. The concepthas been so generally accepted, that it will cause tremors among some.Just because someone does it, does not make it right.

Arc-mapping has been so improperly misapplied and erroneously used tovalidate an area of orign that a different term should be used to trace thearcing on a circuit.

Arc-tracingor some similar term should be used to identify a particularcircuit activity.

Based strictly on the figures, the only thing known for sure is that Ddid not occur first, since another fault is further down the line.

Arc tracingwhich fault occurred first?

A B C E F

L1 L2 L3 L4 L5

X

X

X

X

X

X

D

Arc tracingwhich fault (x) occurred fir

A B C E F

H1 H2

X

X

X

D

Main Breaker

Arc tracingwhich fault (x) occurred fir

Floating neutral created heat & corrosio


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2.9 FAULTFORMSElectric faults can follow three forms direct, breaking, and highimpedance faults.

A relatively low impedance, or direct, fault creates arcs across aninsulating material (or air). These type faults generate intense localizedheat, high temperature ejecta, and loss of material (divots) in conductors.

These type faults are those most easily recognized, particularly by thoseless experienced in electrical failure.

Faults created by making or breaking an electrical connection, such asswitching or pulling apart energized cable. These type faults have a veryhigh frequency component and a resulting sudden increase in voltage.They can damage insulation, particularly in areas where electricalinductance is high, such as at a bend in wire. These are sometimereferred to as parting arcs, though this is an unnecessarily limitingterm.

A relatively high impedanceconnection fault is a very frequent cause offires. This type fault is common when electrical contacts misalign, or

where insulation on cables is partially damaged, but not completelyremoved. A loose connection is actually a high impedance connectionfault. This type fault results in localized heat that can easily exceedignition temperature of common combustibles.

1. The most dangerous characteristic of the high impedance type faultsis that they draw current more consistent with a load than a short.Protection systems, such as fuses and circuit breakers, would notoperate to prevent overheating from this type fault.

2. From our research a fault with an impedance as low as cancause temperatures to exceed 700F.

3. Faults generating heat as low as 11 23 watts has been shown tocreate enough heat to initiate combustion. There are indications thatthe amount of power required may be even lower.

Example: On a twelve volt circuit, such as on a vehicle or wall-wartpower supply, a 23 watt fault would draw approximately two (2) amps.This is a much lower current draw than can be detected by simple fusing.

Risks: High impedance connection faults do not create an easilyidentifiable arc, and thus are not easy to identify visually.

2.10HEAT TRANSFEROnce heat is generated, in order to have a fire, the heat must be

transferred to other locations. Energy always transfers from a warmersource to a cooler place. There are three vehicles for heat transferconduction, convection, and radiation.

These obviously are closely related to heat sources. Good electricalconductors tend to be good heat conductors.

Conduction is heat transfer from one material to another by directcontact.

Convection is heat transfer by fluid currents from one region to another.The fluids can be liquid, which gives better transfer, or gas, which givesless transfer.

Heat transferthree vehicles

Conduction

Convection

Radiation

High resistance connection caused fire

Bend in conduit creates higher inductance

Direct faultarc through char


25/155


Radiation is the heat transferred by solids, liquids, and gases in the formof electromagnetic waves that occur due to elevated temperatures. Nocontact or circulation is required.

Note the illustration of the three vehicles of heat transfer. Conductionoccurs in the handle due to direct contact. Convection occurs in the fluiddue to the circulation between the hot and cold regions. Radiation occursthrough air largely due to infrared waves.

Heat propagates the results of a failure. Heat patterns and metal conditionare used to ascertain the type of heat transfer and the source of theenergy.

2.11 TEMPERATURE AND POWERA failure is related to many components and can be expressed in manyways, all of which are related. The relationships will be simply statedwithout mathematical complications. A later chapter covers themathematical treatise in detail, for those interested.

Elevated temperature is often the first visible manifestation.

Ignition is dependent on the temperature.

Temperature is the environmental energy over the conversioninefficiency called entropy.

Energy over time is the power.

Power density is the concentration of power over an area.

Power is the product of the current squared and resistance.

From these relationships, there is clearly an interaction of electricalenergy to temperature and a resulting potential for failure.

2.12 FIREFor a fire to occur, there have traditionally been three requirements -fuel,ignition source, and oxidizer. Some sources modify the definition toinvolve a sustainable chemical reaction.

Fuelis a combustible material that that provides energy. It will burn orrapidly oxidize. The result is a reduction to its base chemicals.

Ignition is the process of initiating combustion or catching fire. It resultsin elevated temperature of the combustible material.

An oxidizer is a substance that allows combustion to take place. Themost common oxidizer in standard combustion is oxygen. Oxygen is an

element that combines with most elements, is essential for plant andanimal respiration, and is required for nearly all combustion. It comprisesabout 21% of the air. Chlorine and other halogens are also rapidoxidizers.

2.13 REVIEWA failure can result in catastrophe, such as fire. There are numerouscomponents to the cause of a failure. First is how items fail.

Conditions are the following:

Seldom do systems

have problems when

only one component

is improper.

Failures andcatastrophes are the

result of multiple

conditions.

Thermocouple temperature

Heat patterns on stainless microwave


26/155


energized cause energized result de-energized

Failures are are the following:

insulation loss connections

transients

Sources of ignition areare the following:

connections sparks arcs

Non-contactignition is radiation.

Heat transferis byare the following:

conduction convection

radiationFire requires the following:

combustible material ignition source oxygen

2.14BIBLIOGRAPHYILLUSTRATIONSSelect photos courtesy of following. Permission requested, pendingresponse.

Connections,

http://www.flirthermography.com/images/gallery/SPLi_irA0716_005.jpg

Microwave metal, Photo courtesy Rory Earnshaw,http://www.popsci.com/diy/article/2003-09/smelting-microwave

Welder,https://reader009.{domain}/reader009/html5/0410/5acc7b8ca947e/5acc7b9e5

Weld splatter,http://www.mig-welding.co.uk/gasless/gasless-weld.jpg

Weld through,https://reader009.{domain}/reader009/html5/0410/5acc7b8ca947e/5acc7b9f0


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CHAPTER 3WHY ITFAILS-

CAUSE OFFAILURE

3.1 INTRODUCTIONThe previous chapter looked at how equipment fails and the contribution

of this failure to a fire. This chapter will discuss why equipment fails.The how is more associated with the equipment while why is morerelated to the process of design, manufacture or use of the equipment.

Seldom do systems have problems when only one component isimproper. Failures and catastrophes are the result of multiple conditions.

But forone of the problems, there would not be a failure.

As an example, a hair dryer may have a fault. There is no consequenceuntil power is applied. It was not the electric power that caused thefailure, but this was a necessary ingredient. Failure analysis must look atallthe contributing factors to determine which is the crux of the problem.

Often there are multiple contributions to the failure. The interaction ofthese different factors must be identified in order to determine theconsequences of each.

3.2 WHY?CAUSE OF FAILUREThere are three parties that may contribute to a failure supply,product,and user.

Each has a unique role and experience level. Therefore, the responsibilityfor segments will be different.

Supply is used to describe the electrical system up to the point that theuser has some action such as turning on a switch or plugging in an

appliance. Supply has three levels utility, building, and appliance. Thesupply then includes the utility as well as the electrical installer.

The utility operates under the National Electrical Safety Code (NESC)and is usually regulated by the state. The installer operates under the

National Electrical Code (NEC) and is licensed by the state or localjurisdiction. If the utility, or utility contractor, performs work on thebuilding, such as relocating a supply point, the utility is also the installerand must follow theNEC.

Both industry standards have a similar charge for safety.

NESCArticle 010 Purpose states The purpose of these rules is thepractical safeguarding of persons during the installation, operation,or maintenance of electric supply and communication lines andassociated equipment.

NECArticle 90.1(A) Practical Safeguarding states The purpose ofthis Code is the practical safeguarding of persons and property fromhazards arising from the use of electricity.

The Why of a supply failure is a result of problems with the installation,

operation, ormaintenance.

Productis used to describe equipment and items whether on the supplyside or the user side.

Failures & catastrophesare the result of multipleconditions.

Failure Analysisdetermine cause offailure -how equipment failswhy equipment failed

NECelectrical standard

NESCutility standard


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The Why of a product failure is a result of defects in design,manufacturing, ordistribution.

Userdescribes the person that employs the product and the supply. Theuser is not assumed to be knowledgeable in the supply or product designor manufacture.

Why the usercan cause a failure is through misuse, abuse, orneglect.

3.3 PROCESSProductdefects are the result of design, manufacture, and distribution.Design is an inherent problem with the product, but it may be manifestonly under certain circumstances. Manufacture is an occassional problembecause of manufacturing tolerances. Distribution is the process of

getting the product from the manufacture to the installer / user andinvolves storage and handling damage.

Supply fails because of problems with the installation, operation, andmaintenance.

Installation can be associated with the product, supply, or user. It willseparated from those since a different party often makes installation of anappliance. Installation is often directed by industry standards to assurecompliance with safe practices at the time.

Operation includes how the device is used. This would include thingssuch as input power quality, ambient environmental conditions, and

loads placed on the device. Maintenace is how the device is taken careof. This would include lubrication, cleaning, and repair.

The usercan cause a failure through misuse, abuse, orneglect. Misuse isimproper application of the device. In essence misuse is applying thedevice in a way it was not intended. Abuse is damaging the device.Neglect is ignoring the device and allowing it to deteriorate.

There is clearly an interaction between the processes and their failureconsequences. For example, neglect will impact maintenance, which mayshow a design or manufacturing defect.

3.4 PHYSICSPhysics identifies the source of the scientific system that contributes to afailure. Physics are electrical, mechanical, and chemical systems. Eachproduces a thermalresponse because of the energy conversion from oneform to another.

The physics describes both a system and a type of failure. For example,an electrical system can fail because of mechanical and chemical effects.

Electrical systems involve the flow of electrons, magnetic effects, andoptical sensing. Electrical is associated with wires, electro-magneticradiation, and light. Electrical failure is because of loss of insulation(voltage effect) and poor connection (current effect) with time, or fromtransients.

WhyCause of Failure !

Supply: installation, operation, maintenanceProduct: design, manufacture, distributionUser: misuse, abuse, neglect

Typical supply manual

Switch contacts misaligned

Hairdryer inlet blocked

Electrical, mechanical, chemical


29/155

Chapter 3 Why It Fails 29

Mechanical systems involve fluid flow and physical items that can betouched. Mechanical systems include HVAC, plumbing, and machinery.Electrical systems can fail because of mechanical conditions.

Chemical systems involve processes and material reactions. Chemicalsystems include hydrocarbons and plants. Electrical systems can failbecause of chemical reactions.

Thermalenergy is a consequence of each of these physics processes andcan be the result of any or all. Thermal energy is measured bytemperature change.

To make the analysis more interesting, mechanical, and chemicalsystems generally have electrical energy. Therefore, the separationbetween systems is very intertwined, and the interactions are subject tointerpretation.

3.5 COMPONENTS OF SYSTEMAn electrical system consists of three networks - source, path, and

feedback.Each of the networks has three elements. The source includes

supply, return, andprotection. The path includes conductors, switch, andconnections. The feedback includessensor, controls, and load.

SYSTEMsupply

Source return / strayprotection

conductorsPath switch

connection

sensorFeedback controls

load

The resulting system has nine components. Each component of thesystem is subject to electrical, mechanical, and or chemical effects.Furthermore, each can be be attributed to the product, supply, and/or userparties.

LoadControls

SwitchProtection

Supply

Connect Sensor

ConductorReturn

The source is the energy input. Supply problems include power qualitysuch as voltage variation as well as transients. Return problems arealternate or stray paths including grounds. Protection is fuses, breakers,and surge systems. Protection problems include improper size andconnection.

Cable, phone, electric source

Thermal - something got hot

Mechanical damage to cord

Chemicals


30/155


Thepath is the route of the energy. It involves the conductors or wires.The switch is the device to break and control the path. The connectionsare the joints between different conductors. The problems with the pathare predominantly associated with heating from poor connections andhigh resistance.

Thefeedbackis the control of the load. The sensor detects the conditionto control, such as temperature, speed, or light. The controls are thecircuits including electronics and relays that modulate the load. The loadis the energy conversion output to the user. Load can be mechanicalmotion, heat, or light.

3.6 MISSTEPSIn addition to the equipment and the physics, failure of an electricalsystem may be a consequence of missteps, misques, and mistakes. Thethree missteps are mis-size, mis-construction, and mis-material.

Mis-size of conductors and protection can result in excessive current andresulting heat.

Mis-construction will provide inappropriate paths for current and createvoltage stress.

Mis-materialis improper material for the application. For example, a lowtemperature insulation may melt when exposed to heat.

3.7 DETERIORATIONEquipment and materials deteriorate with age, environment, and use. Inaddition, users can hasten deterioration by damage, wear, and

application.

Deterioration can eventually lead to failure and associatedcatatrophicconsequences. Deterioration and wear are normal result of ageand use. Nevertheless, deterioration from old age should not result inignition.

3.8 PROBABILITY FACTORSThe probability of failure and resulting fire depends on three factors -

proximity to combustibles, cooling loss, and exposure time. This is avariation of the three requirements of a fire - fuel, ignition, and oxygen.

Proximity to combustibles involves material properties, distance, and thearea of exposure.

Cooling loss implies barriers to conduction (heat sink), convection

(circulation), and radiation (air flow). The barriers can be from blockedair paths or failure of fans. Lint build-up can block air flow and can becombustible.

Exposure time indicates heat exposure that allows temperature to elevateto igntion.

As proximity decreases, cooling loss increases, and exposure timeincreases, the probability of failure increases.

MIS-STEPS

Mis-size

Mis-construction

Mis-material

DETERIORATION

Mechanical User

Age Damage

Use Wear

Environment Application

Ground resistance > 25

60A wire feeds two 60A breakers

Actual TCO temp: 285F, wire rating: 221F


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3.9 OUTSIDE INFLUENCETransients are one of the electrical areas that could precipitate failures.Transients that cause failure are frequently from an outside influence.The influence can be utility, weather, or through the earth. Each has aseparate chapter devoted to the issue. Only an introduction is noted atthis point.

These outside influences are frequently ignored by some investigators asoutside the realm. A quip heard is You cannot subrogate against God orthe utility which acts like god. In essence, the comment implies no oneis responsible. That simply reflects an incomplete understanding.

If a new roof leaks, it is because of weather in the form of rain, which isan act of God. While God is responsible for the rain, the installer ormanufacturer is responsible for the damage. Lightning is no different.

One of our papers was titled Lightning Damage: Act of God or Act ofNegligence? The key word is damage. As the paper illustrates, lightningand weather is an act of God, but the damage is an act of negligence.

In virtually every instance of outside influence, the damage caused isbecause something was done improperly. In most cases it is non-compliance with an existing standard, code, or law. So, you candetermine the cause and assign responsibility for damage.

A few examples illustrate the issues.

1. Lightning in the area results in failure of flexible gas line. Thereare usually installation and manufacturing problems.

2. Power outage results in appliance failure and fire. There areusually code problems by the utility or installer. There may alsobe manufacturing deficiencies.

3. Someone is shocked and later there may be a fire. There is a

code discrepancy by the installer, utility, or manufacturer.

4. Lightning storm results in appliance failure and perhaps fire.There is probable code incompliance by utility and installer.

As an example, the Empire State building in New York City has beenstruck by lightning multiple times each year, yet it is undamaged by theintense energy, because the installation is proper. Note there are usuallymultiple streamers from the single stroke of lightning. The result isseveral individual strikes associated with a stroke.

If there is a fire associated with conductors in earth, weather, andelectricity, there is a probable non-compliance with codes and hence a

responsibility for the damage.

3.10 ELECTRICAL MEASURENumerous impact and effects of failure have been discussed. Regardlessof the system, mechanism, or problem, electrical failures are the result ofone of two electrical issues (voltage and current) and associated time.The issues are dependent on the only items that can be measured.

Loss of insulation is voltage related.

Poor connection is current related.

Microwave heat-sink and fan

Generator refueled when hot

Controlled lightning*


32/155


Transients and heat are time related.

That is all there is. There is nothing else to describe electrical failures.

3.11REVIEWA failure can result in catastrophe, such as fire. There are numerouscomponents to the cause of a failure. Why it fails is often associated with

a personal action.

Parties to failures are supply, product, and user.

Physics describes both asystem and a type of failure.

electrical mechanical

chemicalThermalis a consequence of energy conversion of physics processes

A system is comprised of three networks - source, path, and feedback.

Missteps are

mis-size mis-construction mis-material

Deterioration of mechanical occurs with

Probability of failure and resulting fire depends on three factors

proximity to combustibles cooling loss exposure time

Electrical failure is related to the measures.

Loss of insulation is voltage related. Poor connection is current related.

PARTIES

Supply Product User

Installation Design Misuse

Operation Manufacturing Abuse

Maintenance Distribution Neglect

SYSTEMsupply

Source return / strayprotection

conductorsPath switch

connection

sensor

Feedback controlsload

DETERIORATION

Mechanical User

Age Damage

Environment WearUse Application

Failure should not cause fire!

Lightning control

Thats all there is


33/155


Transients and heat are time related.

3.12 BIBLIOGRAPHY-ILLUSTRATIONSSelect photos courtesy of following. Permission requested.

1. Lightning,http://turkish.wunderground.com/data/wximagenew/g/GrahamF/

4.jpg


34/155


35/155

CHAPTER 4HEATINGDEVICES

4.1 INTRODUCTIONAll electrical systems generate heat. Heating devices are electricalappliances and apparatus that use heat as a primary component of theirfunction. Heating devices include space heaters, heating ventilation

furnace, clothes dryers, hair dryers, hair irons, clothes irons, electriccook-tops, electric ovens, light fixtures, microwave ovens, and similarequipment. Clearly this is a common use of electrical energy.

Heating devices can be broken into three categories based on how theyare mounted or operatedfixed,portable, and handy (hand operated).

The heating units described above are noted by two major features: Firstthey are electric powered and second they have an electric driven heatsource. In many cases, there is a high temperature surface of a resistiveheating element that can be involved.

Risks: In addition to problems that happen with any electrical device,

there are some that are particularly associated with heating devices. Anycomponent of a system can fail. Every type of failure can occur.

Where particular risks are noted, they are common conditions. Most ifnot all of the issues, we have personally observed.

4.2 THERMAL CUT-OFFSThe operating temperature of a device is generally controlled by athermostat. In order to maintain a target temperature, the device increases

Electrical Failure Analysis for Fire and Incident Investigation

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