Mercer Island Electric Upgrade Project

Mercer Island electric upgrades

Project updates

As this work is in its early stages, you may notice PSE staff and contractors in the project area conducting fieldwork, such as soil testing or surveying existing infrastructure.

Project overview

The electric infrastructure that serves Mercer Island is aging and needs to be replaced to create a more reliable and resilient power grid.

PSE plans to replace the underwater electric cables that serve Mercer Island, increase the cables’ capacity, and make upgrades to the four cable stations located at each end of the cables (see project area to the right). By investing in these improvements, PSE will:

Minimize the risk of outages and unplanned repairs
Support increasing electrification and the island’s future energy needs
Increase service reliability for Mercer Island businesses and residents
Support mobility across the region, including energizing Sound Transit’s East Link light rail line and WSDOT facilities on the I-90 bridge between Seattle and Bellevue
Strengthen the system’s resilience against severe weather

To help ensure continued electric service during construction, PSE will install a temporary overhead transmission line along the south side of I-90 before beginning construction on the underwater cable crossings. This temporary line adds redundancy to the electric system, reducing the risk of outages during construction.

Photo renderings

Please note, these photo renderings are for discussion purposes only and may change pending public, regulatory and utility review.

Temporary overhead transmission line (Barnabie-Enatai)

Existing: I-90 bridge looking east.

Temporary: I-90 bridge looking east.

Existing: Looking east from Barnabie Cable Station.

Temporary: Looking east from Barnabie Cable Station.

Existing: Looking west from Enatai Cable Station.

Temporary: Looking west from Enatai Cable Station.

Map of Mercer Island showing island in Lake Washington and including surrounding highways

Project area (Click to download)

The northern cable crossing is located adjacent to I-90 between the Barnabie (Mercer Island) to Enatai (Bellevue) cable stations. This crossing includes both transmission and distribution cables. The southern cable crossing is located between the Flood (Mercer Island) and Quendall (Renton) cable stations and includes transmission cables only.

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Process

PSE is currently working on engineering and permitting and conducting initial outreach about this project. Throughout this project, we will keep the community informed of our progress, opportunities to engage, and potential impacts.

Chart of Mercer Island electric project timeline

Schedule

Below is our current schedule for construction of each phase of this project. Note, this schedule could change depending on the progress of permitting.

Mercer Island Schedule