The Martha’s Vineyard Commission Thursday unanimously approved Comcast and NStar’s application to install an undersea cable to provide backup service to the Island.

NStar and Comcast requested approval for the installation of a 4.5 mile undersea hybrid fiber optic and electric cable between Falmouth and Martha’s Vineyard, with the cable going underneath the sea floor and coming to land on Squantum avenue and Main street in Vineyard Haven.

The project was first presented to commissioners in December, with NStar representatives saying that out of four existing NStar cables coming to the Island, one does not work. The additional cable would provide redundancy to ensure that service isn’t interrupted, they said.

The cable will end in manholes around the Vineyard Sound’s edge, and from the manholes the cables will be separated and routed in different directions. According to commission documents, construction is to begin in fall 2013 and last no longer than four months.

At the meeting Thursday, commissioner Leonard Jason Jr. said the West Tisbury board of selectmen requested that two fiber cables should be set aside for municipal use, and he wanted to make that a condition of approval. Other commissioners noted the Comcast had balked at that request. Mr. Jason’s amendment was voted down.

In a continuation of a public hearing about Verizon’s proposal to install a cell tower off New Lane in West Tisbury, the wireless company announced some changes to the proposal: the height of the proposed tower is slated to be reduced from 80 feet to 66 feet, and, unlike previously-suggested locations, will be located outside of the coastal district. Verizon has said the proposed tower would improve cellular coverage in the area around West Tisbury’s town hall.

The project has led to concerns from neighbors and residents that the tower would be a visual disturbance, while others have supported the project because it would improve cellular service.

“It’s obtrusiveness has been reduced,” said Carl Gehring, who appeared on behalf of Verizon. Verizon has said it prefers a monopine (fake tree) design, which could allow other carriers to use the tower, as opposed to a stealth monopole. Several residents have objected to the monopine idea.

Tucker Hubbell, the chair of the West Tisbury zoning board of appeals, said he didn’t want to see the pole restricted in size, because the town might prefer options that would allow more than one carrier to use the tower, and the choice between a stealth pole and a monopine should be up to the West Tisbury zoning board.

“Virtually the entire opposition to this is aesthetic, and that is essentially a regional issue,” commissioner Doug Sederholm said. “I don’t know how we can possible abdicate responsibly to a town board on this issue.”

The project now moves to a post-public-hearing land use committee review.