Rio Rico-Harshaw 138kV Transmission Line Project

In April 2023, the Arizona Power Plant and Transmission Line Siting Committee voted unanimously to grant UNSE’s application for a Certificate of Environmental Compatibility (CEC) for the Rio Rico to Harshaw 138 kilovolt (kV) Transmission Line Project. The Arizona Corporation Commission reviewed and approved the CEC in June 2023.

The Rio Rico to Harshaw Line will involve the construction of an approximately 19 mile, single-circuit 138 kV transmission line mounted on steel monopole structures. The project will interconnect UniSource’s existing 138 kV transmission system to the proposed Harshaw Substation through a Proposed 138 kV switchyard in Rio Rico.

The line will serve the Hermosa Project, a mine exploration project in Santa Cruz County owned by Arizona Minerals Inc. (AMI), a subsidiary of South32, while improving service reliability for residential and other electric customers in the vicinity, including the Flux Canyon, San Rafael Valley, Washington Camp and Lochiel areas. UNSE’s existing 13.2-kV distribution line does not have sufficient capacity to support current and future energy needs in these areas while also satisfying the Hermosa Project’s anticipated energy requirements.

For project related inquiries, please send an email to or call (833) 783-0396.

Project Details

UniSource Energy Services: Additional documents

Additional documents

Additional information