Classification societies weigh costs, safety of aluminum power cables


Historically, classification societies have only approved aluminum power cables for limited use on vessels. But in June, DNV GL, one of the world’s largest classification societies, announced new general type-approval standards that clear the way for the use of the cables in a wide variety of areas, including propulsion.

The type approval is valid for five years and applies to any DNV GL-classed vessel or offshore oil rig, representatives from DNV GL said. But other classification societies have reacted with skepticism to DNV GL’s announcement, citing safety concerns with aluminum and international standards for shipboard power cables.

Type approval of aluminum came at the request of Sweden-based Amo Specialkabel and at least one other cable manufacturer, according to Ivar Bull, principal engineer at DNV GL. Representatives from Amo Specialkabel declined comment for this story.

In order to issue type approval under the standards of the International Association of Classification Societies (IACS), DNV GL had to test the aluminum cables in a real-world situation, Bull said. For the past three years, experts from Amo Specialkabel and DNV GL tested the cables on Olympic Artemis, a support vessel owned by Bibby Offshore, a company based in the United Kingdom.

“Aluminum cables supplied the power to one of the ship’s thrusters,” Bull said. “It worked very well, and when we inspected the terminations and cables, (there were) no hot spots.”

Standards for testing
According to The Aluminum Association, a trade group based in Arlington, Va., use of aluminum in electrical wiring has grown rapidly since the end of World War II, and it has become the conductor of choice for utility companies. Bull said this is largely due to the metal’s lower weight and cost compared to copper cabling, even though copper is a better electrical conductor.

But IACS standards have long favored copper cables for most uses on vessels. The organization’s unified requirements for electricity, Part 7 (UR E7), state that electrical cables not only need type approval by a classification society but also must comply with International Electrotechnical Commission (IEC) standards.

Current IEC standards state that shipboard power cables should be made of copper. The IACS, however, does allow for exceptions to these guidelines. The final paragraph of UR E7 states that any cable not tested in accordance with IEC standards must be “of an equivalent or higher safety level.”

“It basically says, ‘We want copper cables, but if you want to use something else, you have to demonstrate that it works.’ You’ve got to prove that whatever you’re installing meets or exceeds those (IEC) standards,” said Demetri Stroubakis, director of corporate global business development for the American Bureau of Shipping (ABS), a Houston-based classification society.

A technician verifies the condition of cable terminations by thermography.

Courtesy DNV GL

DNV GL said that the aluminum cables on Olympic Artemis stood up to rigorous testing. According to Bull, the tests showed no sign of electrical resistance — a major cause of hot spots — especially at the crucial termination points.

DNV GL said that a survey of Olympic Artemis confirmed perfect connections in the conductors after more than 11,000 operating hours. This cleared the way for the society to issue a class program, CP-0409, containing the design, testing and documentation requirements for type approval of terminal lugs used to connect aluminum cables.

The program details several tests that aluminum cables must pass, including watertightness, electrical resistance and salt mist analysis. Nikos Spath, head of media and public relations at DNV GL, said the testing program was developed based on information gathered during the Olympic Artemis pilot installation.

Weight and expense
Due to the inherent competitiveness of the shipping industry, as well as changing technology, DNV GL representatives believe more operators may soon consider aluminum as a viable alternative to copper.

“There’s lots of disruptions in the market, and everyone looks for ways to save costs,” said Simon Adams, senior communications manager for DNV GL. “Competition is really fierce in the market for shipping.”

According to Bull, copper is about three times more expensive than aluminum. He said that aluminum cables require more expensive terminations and installation procedures, but he still has faith in the metal’s long-term competitiveness. Aluminum’s lower weight also can play a big role in its attractiveness to operators.

“The weight of cables can be replaced by more cargo, or if the cargo is kept constant, you will have (lower) fuel costs if you have a lighter vessel,” Bull said.

Recently, the drive to reduce emissions and fuel consumption has given rise to electric and hybrid propulsion systems in the maritime industry. DNV GL representatives believe this trend bodes well for the future use of aluminum.

Manufacturers like ABB Marine Systems, a branch of Switzerland-based multinational corporation ABB Group, acknowledge that electric propulsion systems typically demand much more cabling than their diesel counterparts.

“Additional cables are needed from generators to the main switchboard, from the switchboard to frequency converters, and from there to the propulsion motors,” said Antti Lehtela, contract manager for ABB Marine & Ports.

Electric propulsion systems, like this Azipod unit from ABB Marine Systems, typically require more cabling than diesel systems. Advocates say aluminum holds promise for such applications because it is lighter and costs less than copper.

Courtesy ABB Marine Systems

Safety considerations
Despite the lower cost and the growing variety of uses for aluminum, Stroubakis said that power cables must perform consistently for the duration of a vessel’s designed life cycle. He expressed concern with the relatively short life cycle of aluminum power cables, noting that their conductivity and insulation tends to degrade over time when exposed to marine conditions.

Stroubakis also believes operators have to take safety into account when weighing aluminum against copper.

“Copper, as it oxidizes, remains conductive. If copper cable becomes kinked during service, it’s a little more forgiving and less likely to develop hot spots,” he said. “Aluminum, as it oxidizes, turns into aluminum oxide, which is highly resistive and increases the probability of developing hot spots in the electrical system. If there is mechanical damage to the cable during service, that could also create a resistive condition and lead to hot spots, a cable failure and potentially result in a fire.”

However, Bull is confident that the requirements for terminations included in DNV GL’s new class program will minimize the risk of hot spots.

“We know there are possible issues, but these are addressed and taken care of by well-designed and well-tested terminations with the correct installation methods,” he said.

Bull went on to explain that terminations must be covered with tubing to prevent humidity from interfering with the aluminum conductor.

ABS has approved aluminum cables for very specific applications, but it isn’t considering extending a general type approval for them, according to Stroubakis. When asked about aluminum power cables, Daniel Giani, regional chief executive for Bureau Veritas, said his classification society only accepts copper, citing IEC standards. He did mention that Bureau Veritas is working on certification of aluminum bus bars.

Stroubakis said that ABS recognizes owners’ concerns about construction costs, but he strongly emphasized that IACS requirements exist to promote vessel safety, which is why they are included in ABS Rules. Bull believes that operators don’t have to sacrifice safety in order to save money if they want to adopt aluminum.

“Copper cables are easier to terminate or connect, but when it’s done correctly, we (are) very confident that based on this testing and knowledge about possible issues, we have achieved equivalent safety levels,” Bull said.

By Professional Mariner Staff