New Jersey utility brings in trenching sled to bury underwater lines

underwater transmission line trenching sled
Image credit FirstEnergy Corp.

Earlier this month, Jersey Central Power and Light completed replacement of an underwater high-voltage transmission line which stretched more than a mile across Barnegat Bay along the Tunney-Mathis Bridges.

The work by JCP&L, a subsidiary of FirstEnergy Corp., was done to enhance electric service reliability to New Jersey’s barrier islands.

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Dredging operations in recent years are believed to have damaged the underwater transmission line that ran through the area, necessitating its replacement. The new 34.5-kV line is one of four high-voltage power sources serving approximately 30,000 JCP&L customers on the barrier islands, including the communities of Point Pleasant Beach, Bay Head, Mantoloking, Normandy Beach, Brick, Lavallette, Dover/Toms River, Ortley Beach, Seaside Heights, Seaside Park, Berkeley and Island Beach State Park.

The new line now safely sits 10 feet below the bay’s soft, sandy base. Each of the three cables that make up the line are wrapped with 28 strands of aluminum armor wire, providing robust protection and eliminating the need for a bundled armor casing commonly used in underwater power line projects.

“This project supports our commitment to using new, innovative ways to improve service reliability by utilizing an emerging technology that placed the submarine line in a safer location while also minimizing the work’s impact on the bay’s fragile ecosystem,” said Jim Fakult, president of JCP&L. “The new line helps ensure that our barrier island customers will have the reliable service they need in these peak summer months.”

To bury the line, JCP&L brought in a special underwater trenching sled, marking the first time the technology was used by any FirstEnergy company. The sled used water jets at 150 pounds-per-square-inch pressure to blast a trench about one foot wide and 10 feet deep in which to lay the new power cables.

A large barge carried massive reels of armored submarine cable, hydraulic and water pumps, surveillance monitors, control systems, and other gear as it pulled the 12-ton, school bus-sized sled at rates up to 10 feet per minute. As the sled was pulled along the bottom of the bay, the trench simply collapsed behind it, leaving only a shallow depression marking the location of the line. The 5,800-foot crossing was completed in a matter of days.

JCP&L serves 1.1 million customers in the counties of Burlington, Essex, Hunterdon, Mercer, Middlesex, Monmouth, Morris, Ocean, Passaic, Somerset, Sussex, Union and Warren.

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