UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

DATE OF REPORT

(DATE OF EARLIEST EVENT REPORTED): December 21, 2012

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Item 8.01 Other Events

2012 TEP Rate Case

As previously reported, TEP filed a rate request with the Arizona Corporation Commission (ACC) on July 2, 2012. The rate application is based on a test year ended December 31, 2011. TEP’s rate application requests that new rates become effective no later than August 1, 2013.

On December 21, 2012, ACC Staff and several other intervenors filed their direct testimony in TEP’s rate proceeding. The procedural schedule calls for parties to file rate design testimony on January 11, 2013. Formal settlement discussions can begin January 15, 2013. If a settlement is not reached, TEP’s rebuttal testimony is due February 4, 2013 and ACC Staff and intervenor surrebuttal testimony is due February 25, 2013. Hearings before the administrative law judge on either a settlement agreement or a litigated case are scheduled to begin on March 6, 2013.

While the positions of the parties may change through the course of the rate proceeding, the table and text below summarize TEP’s request and the direct testimony filed by ACC Staff and other intervenors.

Testimony filed by the Residential Utility Consumer Office (RUCO) included adjustments that would result in an increase to TEP’s annual non-fuel base rate revenues of approximately $27 million. RUCO’s testimony also included: OCRB of approximately $1.2 billion; a capital structure of 43.5% equity and 56.5% debt; a return on equity of 10.00%; a weighted average cost of capital of 7.28%; FVRB of approximately $1.9 billion; and a return on FVRB of 5.11%. RUCO’s filing indicated that it is still conducting discovery and may modify certain revenue requirement adjustments when rate design testimony is due on January 11, 2013.

Testimony filed by Arizonans for Electric Choice and Competition (AECC) included adjustments that would result in an increase to TEP’s annual non-fuel base rate revenues of approximately $83 million. AECC’s testimony also included: OCRB of approximately $1.4 billion; a capital structure of 42.85% equity and 57.15% debt; a return on equity of 10.10%; a weighted average cost of capital of 7.21%; FVRB of approximately $2.2 billion; and a return on FVRB of 5.30%.

TEP’s rate application also included various mechanisms designed to recover costs between rate cases associated with lost kWh sales due to the ACC’s energy efficiency and distributed generation requirements, investments in energy efficiency programs and costs of compliance with environmental regulations. ACC Staff and certain other intervenors have taken various positions related to such cost recovery mechanisms. With respect to TEP’s proposed Lost Fixed Cost Recovery mechanism, ACC Staff and RUCO supported TEP’s proposal, with certain modifications.

ACC Staff and intervenors proposed various adjustments to TEP’s filing, some of which, if adopted in the final rate order, could cause TEP to write off certain costs. For example:

All testimony filed in TEP’s rate proceeding can be accessed on the ACC’s website at http://edocket.azcc.gov/. The docket number is E-01933A-12-0291.

TEP cannot predict the outcome of this proceeding or whether any of the above-mentioned positions will be adopted by the ACC.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, each registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.