Less known is that the cable systems that tie down at least 10 perhaps hundreds of the power poles planted throughout the backcountry may also pose a threat because they are capable of conducting electricity.
The hazard occurs when support cables loosen and sway in heavy winds, creating the potential for arcing sporadic sparks that can ignite weeds and other vegetation.
The power-pole design was declared dangerous by an independent analyst retained by an insurance company to examine potential causes of the October fires. There is no proven link between the design and the fires, but the consultant's findings have prompted state utility regulators to open their own investigation.
San Diego Gas & Electric Co. says its system is safe and complies with state regulations.
Regular inspections have found no evidence of arcing in the backcountry transmission system, a utility spokeswoman said.
Officials at the California Public Utilities Commission, which regulates SDG&E and other investor-owned utilities, agreed that the 69,000-volt transmission system does not appear to violate regulations.
But they are troubled by the design and said rule changes may be needed to address their concerns, which for now are limited to SDG&E, even though other power companies may use similar systems.
Raffy Stepanian, a PUC program manager in charge of safety and reliability, said he has opened an investigation in light of information compiled by the analyst that suggests arcing has occurred.
This is a very serious concern for me, said Stepanian, who sent a PUC engineer to inspect the poles with the analyst and convened a meeting with SDG&E recently.
The support cables, also known as guy wires and down guys, are designed to help poles withstand the high winds that blow through the backcountry every year. Two metal cables run from each side of the poles to the ground, forming an inverted V.
In some cases, the cables appear to be attached to the poles through a single metal bolt, with no insulators to stop electricity that can come from ground and other currents.
That opens the possibility, albeit remote, that when lightning strikes or power lines are downed by wind, the electricity could move through the ground and circulate through the steel support cables.
Any looseness in the connections between those cables and the metal rods that anchor them to the ground could generate sparks especially when winds increase the friction potentially igniting nearby weeds and brush.
The risk is obvious in communities such as Ramona and Santa Ysabel, which suffered serious damage in recent wildfires.
In burned stretches of those areas, several guy wires recently appeared loose enough to sway by more than a foot, a violation of PUC orders to keep cables taut.
On some poles, black smudges were visible in places where support cables connected by a single bolt were fastened to the 8-foot anchor rods buried below ground.
Along SDG&E's Transmission Line 637, for example, a network of poles and wires that runs east-west across the hills outside Ramona, black patches were visible in at least 10 places where down guys were tied to anchor rods.
To the north, just inside the La Jolla Indian Reservation, cables that support a pole along Transmission Line 682 also were blackened at the point where they fastened to the anchors.
Edward Clark is the electrical engineer who studied the support-cable design as part of his work for an insurance company. He had the smudges tested by an independent lab, which concluded that the material contained carbon an element left behind after a burn.
There should not be any sparking whatsoever, said Clark, whose December complaint to regulators went unheeded until The San Diego Union-Tribune called the Public Utilities Commission. If it's built the way it's supposed to (be), you don't have a problem.
When asked about the smudges, SDG&E said in a statement that at least one black spot singled out by Clark is actually an old paint band applied by the manufacturer. Any signs of burning along SDG&E equipment are probably due to the wildfires, spokeswoman Stephanie Donovan said.
Clark is a former utility field manager from Huntington Beach who works as a consultant and expert witness. Insurers hire professionals like him to hunt for evidence that might help them recover some of the claims they expect to pay in the wake of major calamities.
Clark has testified for and against utilities for years. He was a consultant for SDG&E in 2000 and for SDG&E's parent company, Sempra Energy, on another case as recently as last fall.
He declined to identify the insurer he is working with because executives did not want to discuss his findings publicly, but he said they know he is speaking with the media.
Clark is convinced that the support cable setup caused October's Witch Creek fire. He also blames the 2003 Cedar and Paradise fires on the design, even though a lost hunter was convicted in connection with the Cedar fire and state investigators suspect the Paradise fire was arson.
Clark said he noticed the potential for conductivity within the first hour of his investigation and told his client to alert SDG&E. The insurance company set up a Dec. 17 meeting with utility executives where Clark presented his conclusions.
When the utility failed to respond after that meeting, Clark said, he decided to create a Web site detailing his research. Then he started contacting regulators and the media. I know I pissed off a lot of people, he said. But this is important.
SDG&E confirmed that the December meeting took place but disagreed with Clark's findings.
We looked at the information and discussed it fully, Donovan said. We don't think he's right.
Donovan declined to say why some guy wires on SDG&E's 18,000-mile transmission and distribution system are designed in a way that might allow for conductivity. She pointed out that the design is not prohibited by state regulations. SDG&E officials are limited in what they can say because the utility has been sued by victims of last year's wildfires, Donovan said. But she defended the company's safety practices.
If arcing had been a problem, our maintenance personnel and inspectors would have identified it long ago and we would have sought changes in the state regulatory codes to protect both our customers and employees, Donovan said in an e-mailed statement.
PUC officials said the situation outlined by Clark needs to be investigated regardless of whether it violates existing regulations.
It may come out that there's a need for a rule change to deal with this sort of an issue, said Richard Clark, director of the commission's Consumer Protection and Safety Division.
If that's what needs to be done, we'll do that, said Clark, who is not related to the Huntington Beach consultant. We are extremely concerned.
California is one of a handful of states that write their own power-line standards, so the safety and compliance of SDG&E's equipment is determined strictly by the PUC.
General Order 95, the 575-page document laying out rules regarding electrical transmission, was adopted in 1941 and has been amended dozens of times since.
The setup discovered by Edward Clark does not constitute a technical violation of the order, the PUC said.
Regulations call for guy wires to be separated by at least 3 inches and in many cases 1 foot as a way to prevent arcing. Wires on the poles inspected by Clark appear to meet that requirement because the bolt connecting the cables is longer than 3 inches.
There is no way to determine how prevalent the design is outside San Diego County. No single agency collects detailed data on transmission lines, which vary in design from state to state and region to region depending on local weather conditions such as wind or ice.
A representative for one publicly traded utility said privately that his company probably employs a design similar to the SDG&E system.
Most states rely on guidelines in the National Electrical Safety Code, published every five years by the Institute of Electrical and Electronics Engineers. The institute declined to discuss the down-guy design used by SDG&E.
The Rural Utilities Service, an arm of the U.S. Department of Agriculture, lends money to electric cooperatives so they can upgrade equipment.
Administrator James Andrew said that when utilities connect multiple support cables to the same pole, they usually build in insulators or take other steps to prevent conductivity.
Fires caused by arcing in support cables are a remote possibility, Andrew said. I'm sure there's a fire somewhere that was started by a guy wire.
Experts in electrical engineering contacted by the Union-Tribune said the support system noted by Clark should be reconsidered by regulators and the utility.
Mohamed El-Sharkawi, a professor of electrical engineering at the University of Washington, examined Clark's findings and said they represent a serious safety issue.
If you allow current to go through that guy wire and you have loose fitting somehow, then you would expect there might be some arcing, said El-Sharkawi, an expert on power-system dynamics and control. Somebody needs to look into that.
Martin Graham, a University of California Berkeley professor emeritus who also has researched electrical transmission extensively, said the design appears to be a defect that needs fixing. He said one solution might be to apply some form of chemical or plastic sealant to the connection between the down guys and anchor rods so they are not as susceptible to looseness during wind gusts.
Clark is right; it's a very big problem, Graham said. But if they get the right (sealant), they could probably spray it on and it could last 10 or 20 years.