Where are underground lines in Arizona?

First a quick primer on the two systems—transmission and distribution—that make up the grid:

FERC Transmission vs. Distribution

Underground distribution is extremely common in Arizona, while underground transmission is less common but growing as density increases. Arizona defines transmission as 115kV and above, while FERC defines transmission as 69kV and above. We will use FERC’s definition since that is how the utilities report their data to the federal government.

Notably, SRP does not report its data to the federal government. Thus, we must derive SRP data from state filings.

Underground Transmission Lines

Here are some maps of the largest underground transmission lines in Arizona:

Central Phoenix 230kV ~14 miles

Adjacent to Central Phoenix is an underground line installed by APS 50 years ago. It is currently being refurbished and re-conductored in phases by APS at a cost of about $8 million per mile.

Tempe / Adjacent to ASU and Tempe Town Lake 230kV ~8 miles

Adjacent to ASU and Tempe Town Lake are two miles of four parallel duct banks containing 230kV or 69kV transmission lines. Thus, all in all, it is about 8 miles of underground transmission lines.

Chandler 230kV ~ 7 miles

SRP has placed two 230kV projects underground in Chandler: Price Road and Intel HIP. The Price Road project was a double circuit project (meaning double the conduit and wires per mile). And, Intel HIP was a double circuit and two-wires per phase project (meaning quadruple the conduit and wires per mile). SRP completed these projects at a cost of about $10 million per mile.

Other Recent Underground Transmission Lines

In its 2023 FERC filings, APS said that it had 59 miles of underground transmission lines in its system. Here are some of the other lines they’ve listed in recent years:

As time and data permit, we will add more maps here of underground lines in Arizona.