BRONX, N.Y.—They arrive in wooden coffins and body bags, with yellow "toe tags." The evidence is carefully protected. A team of highly skilled scientists quickly starts the "autopsy" with a visual examination, sampling, and dissection.
But these "bodies" are not murder victims. They're defective electric cables sent by large municipal utilities all over America. The "forensic" experts are engineers from New York City's Consolidated Edison (Con Ed) power utility at the one-of-a kind Cable & Splice Center for Excellence, a $10-million facility in the Bronx, N.Y., dedicated to sussing out the source of the nation's cable breakdowns.
The center opened in July 2003. It was established by members of the Electric Power Research Institute (EPRI), a national consortium of utilities that conducts research on electric power issues, which was eager to avoid future power failures. Con Ed, with its highly respected, 30-year-old failure analysis lab, was the logical choice to diagnose the causes of cable breakdowns in vast metropolitan networks. Con Ed's database contains 80,000 records of cable failures they've analyzed.
"We go to all our different databases to put our information quilt together, considering every potential cause," says Vincent Ammirato, a senior engineer at the Center. Full analysis of a failed cable takes several weeks, after preliminary reports have cited a suspected cause. "Working backwards to correlate with the hypothesis, we perform simulations and test chemistry, hardness, moisture and endurance," he adds.
EPRI members from around the country send as many as 30 cables that have stumped their own company’s best investigators. In addition, the Center's staff of chemical, mechanical, materials and electrical engineers performs about 1,800 mostly visual autopsies on cables that belong to Con Ed.
Cable sections sent in for examination are usually three to five feet (one to 1.5 meters) long and an inch to six inches (2.5 to 15 centimeters) wide. They arrive at the center via plane, train and truck in containers including sealed PVC tubes shaped like shoulder-fired missiles. All samples have been tested to confirm that they contain no significant levels of polychlorinated biphenyls (PCBs), a highly toxic man-made chemical that is often used inside a cable and come with information from the utility about the specific cable or splice and the conditions under which it failed.
It is key, says Neil Weisenfeld, director of the Center, to protect the tubes and transport them rapidly to preserve any possible evidence such as moisture levels in the insulation or marks on the lead covering.
Once the damaged cargo arrives at the center, it is photographed and videotaped—and the autopsy begins on a long rectangular steel table there. "I'm checking for color, oxidation, smell and oil viscosity—everything but taste," senior engineer Richard Ragusa says as he delicately taps on a length of failed cable. Ragusa and fellow engineers Ammirato and Joseph Watts, all in blue lab coats, slice through the cable's layers to carefully photograph, analyze and determine its age.
Sometimes they can immediately determine the likely source of trouble, such as water damage evidenced by visible stains. If still unclear about the cause of a problem, the engineers take the specimen to a room filled with state-of-the-art instruments where senior engineer Ammirato cuts a sample from the outer sheath of the cable section with a diamond saw blade and encapsulates it in epoxy, which holds the metal firmly. A vacuum chamber removes any bubbles in the epoxy, because they might hide defects in the sample, such as a crack.
Twenty-four hours later, after the epoxy has hardened, the solidified sample will be ground, buffed with diamond or silver polish and placed under a microscope. Through heating and cooling a cable's metal grains can change, allowing microcracks to form. These permit water, a possible failure cause, to enter through the outer sheath.
An atomic absorption spectrometer, an instrument that determines the concentration of metal in a particular sample, analyzes the cable's covering, which is 99 percent lead. Tiny amounts of copper, zinc, silver and iron comprise the remaining 1 percent. This outer covering is liquefied with acid, for chemical analysis. The solution containing the metal is sprayed into a flame in the spectrometer. This instrument registers the intensity of a particular color in the flame, which tells the percentage of each element in that specific sample.
Certain combinations of elements have more corrosion resistance. When a corrosion-resistant covering failures, the cause could be abrasion from a cable support (a piece of metal that attaches the cable to the wall of the manhole.)
Next, a titrator, an instrument that measures the concentration of a dissolved substance, searches for moisture in the insulation of a failed cable. If moisture is found, samples from each of the three layers of the flawed cable are tested to determine its origin.
"If more water was near the failure, it's likely that water caused the failure soon after it entered the cable, rather than over a long period of time," says Alyson Barry, a mechanical engineering graduate student at Manhattan College.
The sample is then put through a device which looks like a high-tech, high-speed pendulum, to determine the extent of its deterioration based on the how many bends its insulation can withstand. Associate engineer Lauren Fox says brand-new insulation can endure 50,000 bends or more; these samples snap after just 250 folds, indicating that the cable insulation had become brittle, less pliable, and breakable over time, making it susceptible to failure. “Information about the particular age and type of cable that has become so brittle and breakable is valuable for our database,” Weisenfeld says.
Among the most frequent causes of failure: mechanical damage, water entry and wear and tear—all of which may divert the current away from the designated path within the cable. Underground water, from rain or streams, can enter cables and splices through nicks in the outer covering. Mechanical damage can occur when cables are cut by workers who inadvertently slice it with a backhoe or jackhammer while doing other repairs or construction nearby.
Wear and tear is caused by age as well as the expansion and contraction of the cable resulting from variations in power usage over a typical day, which can gradually rub away the cable's protective coating. A cable’s outer covering may also corrode and crack under pressure from urban stressors such as stray direct current (DC) from nearby subways, which reaches it through galvanic action (a type of energy generated by electric current), or snowmelt containing heavy salt, which can get underground around manholes.
Once the experts pinpoint the probable flaw, the utility that sent this particular cable is notified of failure risks in similar cables, especially those from the same manufacturer or installation date.
The last step in the process is to review all the data to confirm the cause of the failure. For example, one of the cables examined turned out to have been destroyed by rodents. Occasionally, in an attempt to polish and sharpen their teeth, rats gnaw through the lead covering.
Often the center's findings are used as evidence in lawsuits filed against contractors, construction management companies, and manufacturers that failed to recall defective cable materials. But mostly, the intel is used to improve future cable and prevent similar problems. "The more data we can get on each failure's cause, the more valuable our work is to the industry," Weisenfeld says.
"The causes of some system component failures are quite complex. You need very strong technical understanding, plus an excellent lab for dissecting components to understand the root cause of the failure," says Rick Hartlein, director of the National Electric Energy Testing Research and Applications Center at the Georgia Institute of Technology. "The Cable Center is 'CSI Bronx'."