Merrill to Coolidge 69kV Transmission Line Project

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Voltage – 69kV
Estimated completion date – Q1 2027
Location – Arizona, Pinal County, Coolidge – Florence area 

Project Need


The project is needed to increase electric service capacity and improve the reliability of the electric transmission system in the Arizona Public Service (APS) territory in Pinal County between the existing Merrill and Coolidge substations.

Currently, electrical service to the Merrill Substation is supplied from a single source of power flowing in one direction. If there is a power outage on the system, there is limited capacity to redirect power flows to the areas in need. That could interrupt our ability to provide power to customers in the area. The project will connect the Merrill and Coolidge substations to create a looped system, improving reliability in the region.

Project Description and Features

The project involves constructing, operating and maintaining a 69 kilovolt (kV) transmission line between the existing Merrill and Coolidge substations. The 69kV transmission line will be approximately eight to 12 miles long, depending on the route selected.

Similar in appearance to other APS 69kV lines in the area, the proposed 69kV transmission line will be constructed as a double-circuit configuration (three wires per circuit, six wires total) on steel monopoles with a 12kV line built underneath on the same structure, referred to as underbuild. It is anticipated that the monopoles will be approximately 65 feet in height depending on terrain and engineering/design requirements (e.g., crossing roads and other power lines). The transmission line will require a right-of-way or easement approximately 60 feet wide (30 feet on each side of the line) to safely construct, operate and maintain the line.

Project Planning

In early 2023, we initiated a siting study to identify and evaluate alternative routes for the proposed transmission line, assess potential environmental impacts and support the public outreach process.

When developing alternative routes, we evaluate criteria like environmental impacts, engineering and construction feasibility, land acquisition timing and costs, regulatory approvals, potential impacts on existing and planned neighborhoods and input from agencies and the community.

Public Input

An important component of this siting process is to gather input from the public (property owners, residents and businesses) in the project siting area. We have implemented an extensive public outreach and planning process, including public information open houses and newsletters.

On September 14, 2023, we hosted a public open house to introduce the project and encourage public input on the project and several route segment alternatives. The input we received contributed to our siting study and resulted in the identification of three preliminary alternative routes. Now, we want your input on the preliminary alternative routes. We invite you to join us at an upcoming public information open house meeting at the time and location listed below, or online by visiting www.merrillcoolidgeopenhouse.com after December 7. Attendees will be able to learn about the project, the siting process, route alternatives and ask questions and provide input on the location of the new line.

Anticipated Project Schedule

Project Planning 2023-2024 | Permitting 2024 | Construction Q4 2026 | In Service Q1 2027


Open Houses Newsletters Project Maps Fact Sheet
FAQ Page
Comment Form (Opens in new window)  
For more information: Project information phone line: 1-602-812-5829 or toll free at 1-888-687-2144
Project email: MerrilltoCoolidge@aps.com
  Lupe Martinez, Siting Consultant
Arizona Public Service
2121 West Cheryl Drive
Mail Station 3293
Phoenix, AZ 85021
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