Dr Antony Anderson CEng FIEE Electrical Consultant

Dr Antony Anderson CEng FIEE/FIET

Sherlock Holmes on the job - The Importance of Electrical Failure Investigations

(Original version published as "Uncovering the empowering evidence" in Your Witness, May 2009

1   Society depends on reliable electricity

Society depends on the reliable supply of electricity for use in homes, offices, hospitals and factories. Ships, aircraft, trains and automobiles also require their own extensive electrical power systems to power a multitude of on-board electrical and electronic systems, many of which are safety critical.

2     Electrical failures have to be investigated to prevent recurrence.

Toyota Tacoma sudden acceleration  crash
Tacoma sudden acceleration
© Visconi
We take electricity for granted until we get trapped in a lift in total darkness, or an airport baggage carrousel breaks down and separates us from our luggage, or our computer locks up on us just as we are printing an urgent report, or an automobile exhibits a fit of electronic disobedience and accelerates of its own accord into a brick wall or wraps itself round a tree. Then, for a moment, we realize our total dependence on electricity and our vulnerability. We may ask many questions: what went  wrong? why? how soon can the fault can be repaired? what will it cost? how can a recurrence be prevented? who may be to blame?  We call for an electrical investigation.

2    Pinning down causes is difficult and time consuming

winding fault
Inter-layer winding fault showing partially melted conductor - an indication of arcing
Electrical failure analysis - pinning down the causes of an electrical or electronic malfunction - is often difficult and time consuming. In some cases the resultant damage  destroys much of the evidence of the initial cause. With electrical fires, for example, the question may be: did the fire cause the electrical damage or did  the electrical damage cause the fire?  Hasty investigation may cause investigators to reach the wrong conclusions  - arson for example - when more careful sifting and analysis of the fire debris might  have revealed signs of electrical arcing, the potential indicator of an electrical fault. In other cases, electrical machine failures for example, there may be signs of incipient damage elsewhere in the machine that may provide clues as to possible fault mechanisms.

3   Intermittent electronic malfunctions challenge the forensic skills of the electrical    investigator

Fretting and micro-arcing damage on a sensor input pin to a control microprocessor on an automobile automatic stability system
Intermittent electronic malfunctions represent a subtle challenge to the forensic skills of the electrical investigator, because the system may well return to its normal operating state of its own accord and the malfunction may not  reappear for years. Failing to find an intermittent electronic malfunction in the here and now does not mean that there never was a malfunction, merely, that, like McCavity, T.S.Eliot's Mystery Cat,  an electronic system malfunction may leave little by way of a permanent trace behind it. Electromagnetic interference and software malfunctions are, as it were, the hidden paw of McCavity behind many seemingly mysterious intermittent electronic malfunctions, for which no physical fault, in the form of a failed component, may be found. Absence of proof of an electronic malfunction, in a vehicle, for example, is not proof of absence. Unfortunately, investigators often assume that absence of proof is proof of absence. For instance, drivers may come to be blamed, by fallacious argument, for what might well be electronic system disobedience.  

4   Electrical investigations vary in scope and cost.

generator core fault
Core fault damage as seen
during core disassembly

generator core fault damage
Core fault damage from a large generator set out in a sandbox

Electrical investigations. vary enormously in their scope. A  stator core failure in large power station may require a multi-disciplinary investigation team and cost many tens of thousands of pounds expenditure. The cost of the investigation can be justified because of the lost revenue caused by not solving the problem. Investigation of an electrical fire in a vehicle or a building would, in all probability, be on a much reduced scale. Sometimes the failure of a mass-produced component, itself costing very little, may have such disastrous knock-on effects that an electrical investigation quite out of proportion to the cost of the component may be justified. An example would be the investigation of a small hydraulic pressure switch placed in the brake master cylinder of about 16M vehicles built by one American manufacturer that has led to many hundreds of  under-hood fires.

5  Electrical investigations demand a careful and thorough approach

In all electrical investigations a similar careful and thorough approach has to be applied. Firstly there has to be a non-intrusive investigation and only when this has been completed should the more detailed investigation commence. Samples may need to be gathered up and recorded, much as in an archaeological dig. It isn't very helpful to the investigation if nobody records where samples come from!  Likewise photographs  must be taken systematically. Often there is loss of evidence through the taking of poor photographs. The use of a tripod combined with a small aperture allows the depth of field to be maximised, giving maximum clarity to photographs. A watchmaker's eyeglass is ideal for spotting all the interesting electrical clues that may well be much too small to notice otherwise. And it is quite surprising what may be recorded by the use of a good close-up lens.

6    Electrical investigators should keep an open mind as long as possible.

Electrical Investigators should try to maintain an open mind on possible causes for as long as possible. They should fully explore in their report writing even those potential causes that they think unlikely and explain why they have rejected them. Otherwise, they may one day find themselves in court trying to explain why they failed to consider some potential cause which, in hindsight, it is obvious that they should have considered. Such a failure to follow a proper investigation methodology is unlikely to go down well in court!

7   Electrical Investigators should look for the unexpected

meandering interlaminoar
Meandering interlaminar
breakdown in the stator core
of a large generator
Electrical investigators should  look for the unexpected, for what  they have not seen before.  The electrical investigator's  life can full of surprises and that is what makes it so interesting.

Antony Anderson May 2009