American Transmission Co. projects

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ATC completes electric cable replacement in Straits of Mackinac

New solid-core cables operational, electric reliability reinforced and some mitigation work forthcoming

PEWAUKEE, Wis. – American Transmission Co. has completed the process of removing six submarine electric transmission cables and installing two new submarine cables on the lakebed of the Straits of Mackinac. Cable removal began in fall 2020, and the approximate seven-month process to install the new cables and backfill the trench now largely concludes ATC’s Straits Cable Replacement Project.

“This was a unique and challenging project to construct,” said ATC Vice President of External Affairs and Communications Greg Levesque. “The ATC team and our contractor partners worked nearly 45,000 consecutive safe hours on shorelines, aboard barges and in waters up to 280 feet deep. With the project now in service, these two new circuits in the Straits reinforce electric reliability for our local distribution customers and their energy consumers in the state of Michigan.”

ATC partnered with LS Cable Systems America Inc., a subsidiary of LS Cable & System Ltd of South Korea, to produce and install the replacement transmission cables. Durocher Marine, a division of Kokosing Industrial Inc. contracted with LS Cable Systems America to remove the remaining submarine cables and replace both circuits with two, three-phase 138,000-volt cables containing solid dielectric insulation.

“One of our biggest priorities was making sure the original fluid-filled cables were safely removed from the Straits without any fluid release into the water and that effort was successful,” said ATC Consultant Project Manager Dustin Johanek. “The newly installed cables contain solid dielectric insulation instead of fluid so they will not leak if there is a future inadvertent impact.”

In April 2018, ATC’s two transmission circuits were damaged when a ship anchor severed two of the six cables and severely damaged a third. The three undamaged cables were reconfigured to form a temporary single transmission circuit, allowing ATC to restore one electrical connection between the Upper Peninsula and lower Michigan while the dual circuit replacement project took place. Two operating circuits are needed to effectively manage electric reliability within the region.

While installation of the cables is complete, ATC has identified some cable locations within the Straits that will require additional support and erosion mitigation.

“ATC and our contractors made every effort to install and stabilize the cables during construction,” said Johanek. “After completing a detailed survey analysis of the two newly installed cables, we discovered some areas beneath the cables that will require additional support to reinforce reliability and mitigate potential erosion by installing rock fill. Given the allocation of time for permit evaluations and ability to safely perform the marine work, we anticipate this effort will take place in 2023.”

ATC initially received permits from the U.S. Army Corps of Engineers and Michigan’s Department of Environment, Great Lakes and Energy to conduct the cable replacement work and is in the process of filing permit applications with both agencies for the forthcoming mitigation work. Since 2018, ATC continues to collaborate with Michigan tribal nations to gather input and provide project updates.

A full-feature video about the project and construction process can be viewed here.

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ATC is a Wisconsin-based company that moves energy along the regional electric grid in parts of Wisconsin, Michigan, Minnesota and Illinois, serving more than 5 million electric consumers. We are experts at what we do: planning, maintaining, operating and protecting the grid. As the electric industry moves toward renewable generation sources, we are transforming our system to continue delivering energy reliably and safely. We proudly support STEM education programs that empower youth with the skills needed to succeed in tomorrow’s energy workforce. For more information, visit and follow us on LinkedIn and X (Twitter).