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Greenwich Substation and Line Project

Eversource is modifying the Cos Cob Substation to accommodate new transmission lines. We expect to start construction of the new lines and the new Greenwich Substation in early 2019.  


As part of always working to serve you better, Eversource is preparing to construct two, new, 115-kilovolt (kV) transmission lines and build a new substation to improve reliability in Greenwich.

The new lines will extend 2.3 miles from Eversource’s existing Cos Cob Substation on Sound Shore Drive to the new Greenwich Substation at 290 Railroad Avenue. The new lines will run underground, primarily under town streets, including those in Bruce Park.

The project also includes modifications at the Cos Cob Substation located at 12 Sound Shore Drive.

Greenwich project map

Click to enlarge map

Project Facts:

  • Underground route length: 2.3 miles
  • Location: Greenwich, Connecticut
  • Line voltage: 115,000-volt (115-kV) transmission line
  • Substation: One new transmission-level substation and modifications to the existing Cos Cob Substation
  • Siting review by: The Connecticut Siting Council (CSC)
  • Application filing to the CSC: June 26, 2015
  • CSC approval issued: November 9, 2017
  • Cos Cob Substation start of modifications: May 12, 2018
  • Start of preparation for warehouse building demolition and pre-construction site preparation for Greenwich Substation: September 12, 2018

Next Steps (estimated timetable, subject to change):

  • Development & Management (D&M) Plans (construction plans) to CSC for approval: First Quarter 2019
  • CSC Decision on remaining D&M Plans: First - Second Quarters 2019
  • Start of construction on remaining project sections: Early 2019 


Following receipt of the CSC’s application approval, Eversource is required to submit construction plans, called Development & Management Plans (D&M Plans), to the CSC for its approval before construction can begin. These plans include, but are not limited to, further design detail, final site plan, construction sequencing, traffic management plans, work hours and laydown/staging areas. There are multiple D&M Plans for this project.

On February 20, 2018, Eversource submitted the Cos Cob Substation D&M Plan to the CSC. It was approved by the CSC on April 12, 2018.

On May 18, 2018, Eversource submitted the Greenwich Substation Warehouse Building Demolition and Pre-Construction Site Preparation D&M Plan to the CSC. It was approved by the CSC on June 21, 2018.

On October 3, 2018, Eversource submitted the Greenwich 115-kV Underground Transmission Lines D&M Plan to the CSC, including following seven appendices: 

Eversource intends to submit the two remaining D&M Plans to the CSC in the coming months, one for the crossing of Indian Harbor and the other for construction of the new Greenwich Substation. They will be posted here when available.  


Eversource will begin construction of the approved portion of the project after receipt of the CSC's approval of each D&M Plan. Work will be done in sections, rather than continuously in any one area.

Cos Cob Substation

Modifications to the Cos Cob Substation began on May 12, 2018, and will continue through 2019.

Work activities within the existing substation property will include vegetation removal; grading, digging and trenching; installation of new equipment and retaining walls; and then restoration of areas disturbed by the work.

Work hours will typically be 7 a.m. to 6 p.m., Monday through Friday, and 9 a.m. to 5 p.m. on Saturdays. Due to weather or other circumstances, from time to time the crews may need to work longer hours or work on a Sunday.

Greenwich Substation

Preparation for the removal of the existing warehouse and pre-construction site preparation for the substation began on September 12, 2018, and will continue through early 2019.

Preparation includes the installation of a temporary security fence, removal of the building and related materials, vegetation removal, and grading of the site.

Work hours will typically be 7 a.m. to 6 p.m., Monday through Friday, and 9 a.m. to 5 p.m. on Saturdays. Due to weather or other circumstances, from time to time the crews may need to work longer hours or work on a Sunday.

Underground Transmission Line Construction

Upon receipt of required approvals, construction of the new 115-kV underground transmission line will begin. This work is anticipated to start in early 2019 and be complete by the end of 2019. Additional information on the schedule and location of the underground transmission line work will be posted when available.


Beginning with municipal briefings and other community outreach efforts, Eversource engages the community throughout the lifecycle of a project to provide information, answer questions and listen to concerns.

As the project proceeds through construction, Eversource is committed to updating neighbors, businesses, and the Greenwich community about construction activities in the area. 


For more information about the Greenwich Substation and Line Project, please email or call 800-793-2202.