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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

Source: APS Phoenix Line Upgrade Website

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

Source: ACC Docket L-00000D-14-0292-00169, Line Siting Case 169

Source: APS Tempe Town Lake 230kV OH/UG Conversion Project Presentation by Ted Nishioka

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 ~ 3.5 miles

Source: ACC Docket L-00000B-17-0182-00175, Line Siting Case 175

Source: ACC Docket L-02217B-21-0322-00195, Line Siting Case 195

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:

#	Project Name	Location	Year	Co.	kV	Miles
1	County Line-Buyan	Gila Bend	2020	APS	69	4.5
2	Ocotillo-Tempe	Tempe	2020	APS	69	0.8
3	Indianola-Midtown	Central Phoenix	2019	APS	69	0.6
4	Country Club-Midtown	Central Phoenix	2019	APS	69	0.2
5	Commerce-Turf	North Phoenix	2019	APS	69	0.5
6	Commerce-Deer Valley	North Phoenix	2019	APS	69	0.5
7	Dale-Via Dona	Scottsdale	2018	APS	69	5.2
8	Business District	Scottsdale	2018	APS	69	0.78

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