The eave, gutter and downspout where the first fire started.Rear rafter with second fire at eave with minimal charring.Eave flashing lifted showing roofing nail heads and circular charring around points where metal flashing arced.Arcing melted holes in the flashing and burned away the black paint.Eave flashing with burned holes that caused pyrolysis of the wood rafter beneath. Neighbor’s house abuts in the background.Metal flashings make contact between adjacent houses allowing stray electric current.Although there was electrical power wiring below the eave’s fire origin, inspection showed that it did not initiate the fire.Attic below the first fire has only low power wires that couldn’t start a fire, and drop down char that resulted from the fire above and outside.
Broken Utility Wire Causes House Fire
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Neighbors noted smoke showing at the side eave of a Row House. The fire department extinguished the small blaze, and performed “overhaul” by cutting open the roof to assure no further spread of the fire. No obvious cause was noted.
Two days later a similar smoldering fire erupted in an eave fascia board at the rear of the residence. Again no obvious cause was identified but this time several electrical appliances had “popped” or smelled of smoke so the Electric Utility was called to disconnect power until the causes could be identified. At that time the utility “troubleman” discovered that, of the three overhead wires traditionally serving a house, the un-insulated (bare) one, called the “neutral” wire, was broken. He measured and recorded the unbalanced voltages typically found at a house during this type of “open” condition.
Determine Cause and Origin of consecutive residential fires
Resolve seven conflicting forensic reports
Address the veracity of various expert witnesses
Justify subrogation to the Utility Company
Address the homeowner’s claim that all house wiring was damaged and
At the time I was retained, the homeowner had refused the settlement offer of his insurer, refused to repair the damages, and claimed months of lost tenant rent from uninhabitability due to a lack of power. He had retained an independent adjuster thereby establishing an adversarial position with his insurer as well as his electric utility. The owner claimed that the Utility’s open neutral wire had damaged his house wiring system that now must be entirely replaced.
I received several reports. The insurance company had retained a fire investigator who performed a standard C&O analysis. Although he could not specifically identify the mode of ignition, he located the origin to the attic, and concluded that the fire was “probably due to an electrical system failure.” When asked if he had any unusual electrical background or expertise he admitted to none. His judgment of electrical cause would not, on its own, stand up to forensic scrutiny.
An electrical contractor known to dabble in forensic investigations wrote a terse letter stating that the fire cause could not be electrical in nature because there were no electrical wires in the area of the origin of the fire.
A Building Department Electrical Inspector viewed the property and wrote “Verify that the existing wiring and electrical equipment that may have been damaged by overvoltage retains operational integrity.” The owner, a holder of an electrical contractor’s license, “taking literary license,” declared that the Building Department agreed with him that the house wiring could be damaged and must be replaced to current codes.
Another electrical contractor was called in to measure the insulation resistance of the whole house’s wiring. He declared that the wiring tested OK. The owner claimed that his test procedure was faulty and therefore not applicable.
In a letter to his insurance company (through the independent adjuster) the owner stated that he had conferred with several professional acquaintances, both contractors and engineers, who all “felt” that a wiring system exposed to an open neutral condition would be dangerous and must be completely replaced.
Read and analyze the reports
Inspect the Site
Determine the Cause and Origin
Write a report addressing the other opinions
Respond to any critiques of my analysis
Testify at Mediation
On the day of my inspection I met with my insurer-client’s initial fire C&O investigator to benefit from his percipient knowledge and avoid repeating work already done. I verified that there was no electrical power wiring present at the origin of the first fire.
I explained to the owner that during an open neutral condition, although appliances and fixtures can fail from overvoltage, the voltage within the house wiring can never exceed the nominal supply voltage of 240V, well below the 600V rating of the house’s wiring, and excess currents in any of the wiring cannot exceed the safe limits set by the circuit breakers or fuses. He agreed with my logic but could not let go of the feeling that somehow some massive short circuit in his wiring had caused the trouble and its damage must be excised.
As I viewed the charred debris saved from the second eave fire I noticed several perfectly round “heavy char” spots (called “Alligatoring” in C&O lingo for its resemblance to the skin of a reptile) in a field of otherwise mildly sooted wood. I “reconstructed” the eave and flashing using the saved pieces and noted there was a small hole in the galvanized metal flashing coincident with each of the circles of char.
Closer examination revealed that electrical arcs had caused the holes in the metal. From prior experience with open neutral fires, I knew immediately that the electrical current, that was denied passage through the broken neutral wire, had found a path into the bonded heating ducts and the plumbing’s roof vents, and eventually the roof’s metal flashings and rain gutters, then transferred to similar abutting components of a neighboring house and finally back to the power pole.
Only the sheet metal components of a building that could become energized are required to be electrically bonded to each other and connected to the electrical system’s neutral wire. Typically the flashings are only casually connected to each other in a manner that can allow stray electrical current to pass, but could easily generate excessive heating. (All “intended” electrical connections must be made in a manner that minimizes heating to avoid fires.)
Although this path of electrical current and mode of ignition are familiar to me, they are sometimes difficult for others to understand, so in my report, not only did I have to explain this finding, with liberal use of diagrams, in a manner that even a non-technical juror could understand, I also had to address the opinions, qualifications, and egos of the other experts in a professionally appropriate manner.
Upon receipt of my report through his independent adjuster, the homeowner immediately protested, and then commissioned a competing report from a licensed engineer who designed power plants and large transmission lines worldwide, per his visually impressive web page, yet demonstrated no experience with distribution and residential wiring. This engineer, to justify his condemnation of the house’s wiring, proposed that the fires had occurred from a short circuit somewhere within the house that drew so much current that it caused the supply’s voltages to drop from 120 volts to 94 and 58 volts, values he took from the lineman’s report.
To account for both fires this condition would have had to last for three days and would have also caused an extreme brownout in ten neighbor houses, which no one had reported. It would not have accounted for the three day separation between incidents. Further, based on a simple calculation, his hypothesis would have required the service drop wires, normally rated for 200 amps, to carry 2,000 amps which would have caused their insulation to melt; again this was not reported nor observed. This overcurrent was his purported cause for the break in the neutral at the pole. But since this current would have to pass through the house’s wiring to justify the owner’s need for a full wiring replacement, it also had to pass through the breaker panel, which would have tripped the main and possibly a smaller breaker, precluding any house wiring damage.
Although it is professionally appropriate to propose alternate hypotheses to support reasonable doubt, they must not only pass forensic scrutiny, but also a physics reasonability test. Yet professionally it was not enough for me to write a report merely declaring that every other “expert” was just plain wrong. I needed some defining evidence.
I know from the laws of electricity that even in an unbalanced neutral condition the two voltages must always sum to the supply voltage, which in this case was 252V (126+126 from the note). During every open neutral condition, when one leg's voltage goes higher, the other goes the same amount lower. The only consistent interpretation of the troubleman’s measurements is to read the value written after 94 volts as 158 volts, making the sum then 252 volts (94+158). It is much more likely that the troubleman, out of habit, started to write the 94/158 as "94 volts /58 volts" instead of assuming that a logically unsupportable overcurrent existed for three days. A meter misread or display error could explain the difference in his reading 126V/126V/245V and the expected 252 volts.
Although a typical electrical C&O report might take only two pages, my report addressing each expert’s credibility, background, and possible point of view, required 22 pages to finally resolve this case.
The electrically caused fires resulted from a broken Utility Company wire
The origins were at the roof’s eaves
No electrical power wiring was present at the origins
Electrical current was diverted through roof flashings
Poor electrical connections at the flashings initiated pyrolysis in the wooden fascia boards that eventually smoldered
At mediation, in a PowerPoint presentation, I showed in graphic detail how the grounding and bonding wiring required by the National Electrical Code created a situation during an open neutral where electrical current can flow through roof flashing. Faced with an NEC proscription that the earth may not be used as the sole grounding conductor the Utility still balked at a settlement, even though the mediator, who was a retired judge, initially pondered why they would even attempt to delay.
After much back-and-forth it appeared that they might have intended to use this claim to create a case law precedent potentially useful in other litigation. The technical forensic presentation proved so overwhelmingly convincing that the utility yielded, remitting a satisfying sum in subrogation to the insurance company.
Fire Cause and Origin
Power Wiring and Circuits
National Electrical Code (NEC)
General Order 95
Electrician Trade Practice
Lock Out / Tag Out
708 Trancas Street
Napa, CA 94558