Avista Electric Line Extension Schedule 51 Rate Adjustment

Office of the Secretary Service Date BEFORE THE IDAHO PUBLIC UTILITIES COMMISSION March 30, 2026

IN THE MATTER OF AVISTA ) CASE NO. AVU-E-26-02 CORPORATION’S ANNUAL RATE ) ADJUSTMENT FILING FOR ITS ELECTRIC ) LINE EXTENSION SCHEDULE 51 ) ) NOTICE OF MODIFIED ) PROCEDURE ) ) ORDER NO. 36985 On March 6, 2026, Avista Corporation, doing business as Avista Utilities (“Company”) applied to the Idaho Public Utilities Commission (“Commission”) requesting an order approving the update in costs and administrative changes to the Company’s Electric Line Extension Schedule 51 (“Schedule 51”). The Company requested a May 15, 2026, effective date. The Company requested its filing be processed by Modified Procedure, pursuant to the Commission’s Rules of Procedure 201-204, IDAPA 31.01.01.201-.204. The Commission now issues this Notice of Application and Notice of Modified Procedure establishing written comment deadlines.

YOU ARE HEREBY NOTIFIED that the Company’s Schedule 51 electric line extension tariff establishes the estimated costs for electrical infrastructure regularly used in extending electrical service, such as transformers and conduit. Application at 2. The Company represents the estimated costs set forth in Schedule 51 are determined from the recent average costs of the infrastructure. Id. The Company does not propose changing the average costing principle used to determine the estimated costs in Schedule 51. Id. YOU ARE FURTHER NOTIFIED that the Company filed additional documentation including workpapers and work order estimates, to support the cost updates in Schedule 51. Id. YOU ARE FURTHER NOTIFIED that the Company represents it will also update allowances for incoming commercial, industrial, and residential customers. Id. at 3. The Company represents that it calculated the revised allowances under the “embedded-cost methodology approach.” Id. The embedded-cost methodology approach works to make sure the cost for distribution/terminal facilities for each new customer is similar to the costs of the same infrastructure already allocated for in base rates. Id. New customers will have to pay for costs that

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exceed the updated allowances. Id. The Company represents it based the embedded cost calculation on the “Cost of Service study” from its most recent general rate case filing, Case No. AVU-E-25-01. Id. The following is a summary of the Company’s proposed changes to the allowances: Service Schedule Existing Proposed Schedule 1 Individual Customer (per unit) $2,545 $2,755 Schedule 1 Duplex (per unit) $2,035 $2,205 Schedule 1 Multiplex (per unit) $1,530 $1,655 Schedule 11/12 (per kWh) $0.19912 $0.21041 Schedule 21/22 (per kWh) $0.18388 $0.20083 Schedule 31/32 (per kWh) $0.32929 $0.35568

YOU ARE FURTHER NOTIFIED that the Company represents its “Construction & Material Standards” filed with its application reflect the most recent revisions to the “National Electric Safety Code.” Id. at 3-4. YOU ARE FURTHER NOTIFIED that the Company represents it will update the average costs for primary circuits, secondary circuits, service circuits, and transformers. Id. at 4. The following is an overview of the Company’s proposed update to the average costs: Present Proposed Overhead Primary Circuit Fixed Cost $5,536 $5,952 Variable Costs $11.20 $12.04 Underground Primary Circuit Fixed Costs $2,583 $2,754 Variable Costs $13.55 $14.31 Underground Secondary Circuit Fixed Costs $647 $688 Variable Costs $12.75 $13.18 Overhead Secondary Circuit Fixed Costs $2,279 $2,466 Overhead Service Circuit $5.06 $5.56 Underground Service Circuit $10.29 $10.78 Overhead Transformer $5,308 $5,222

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Padmount Transformer $10,003 $9,134

YOU ARE FURTHER NOTIFIED that the Company represents that the contributing factors for the increase in average costs for primary circuits, secondary circuits, service circuits, and transformers are “higher overheads and vehicle costs.” Id. The Company represents the increased vehicle costs are due to expenses for maintenance and repair of the Company’s fleet vehicles and higher fuels costs. Id. The Company represents the higher overhead costs are due to increased costs for labor and benefits. Id. at 5. YOU ARE FURTHER NOTIFIED that the Company represents that based on the current Construction & Material Standards and the average construction costs for 2025, it will update its residential development costs to the following: Residential Developments Present Proposed Total Cost per Lot $ 3,849 $ 3,818 Less: Service Cost $ 516 $ 541 Developer Responsibility $ 3,333 $ 3,277 Developer Refundable Payment $ 2,545 $ 2,755 Builder Non-Refundable Payment $ 1,304 $ 1,063 Allowance $ 2,545 $ 2,755

YOU ARE FURTHER NOTIFIED that the Company will remove language from the tariff to clarify that developers who pay for extension costs described in 4.b.1) can apply for a refund annually for each permanent customer that is connected in the development in the first five (5) years following the start of construction. Id. YOU ARE FURTHER NOTIFIED that the Application is available for public inspection during regular business hours at the Commission’s office. The Application is also available on the Commission’s website at www.puc.idaho.gov. Click on the “ELECTRIC” icon, select “Open Cases,” and click on the case number as shown on the front of this document.

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YOU ARE FURTHER NOTIFIED that all proceedings in this case will be held pursuant to the Commission’s jurisdiction under Title 61 of the Idaho Code, and that all proceedings in this matter will be conducted pursuant to the Commission’s Rules of Procedure, IDAPA 31.01.01.000

et seq.

YOU ARE FURTHER NOTIFIED that the Commission has determined that the public interest may not require a formal hearing in this matter, and that it will proceed under Modified Procedure pursuant to the Commission’s Rules of Procedure 201-204, IDAPA 31.01.01.201-.204. The Commission notes that Modified Procedure and written comments have proven to be an effective means for obtaining public input and participation. YOU ARE FURTHER NOTIFIED that persons desiring to state a position on this Application may file a written comment explaining why the person supports or opposes the Application. Persons who would like a hearing must specifically request a hearing in their written comments and explain why written comments alone are insufficient. Persons interested in filing written comments, must do so by April 23, 2026. Comments must be filed through the Commission’s website or by e-mail unless computer access is unavailable. To comment electronically, please access the Commission’s website at http://www.puc.idaho.gov/. Click the “Case Comment Form” and complete the form using the case number as it appears on the front of this document. To file by e-mail, persons must e-mail the comments to the Commission Secretary and all parties at the e-mail addresses listed below. Persons submitting a comment by e-mail must provide their name, address, and the Case Number under which they are commenting. Persons submitting a comment by e-mail also acknowledge that submitting a comment in an open case constitutes a public record under Idaho Code § 74-101(13), and all information provided by such person is available for public and media inspection. If computer access is unavailable, then comments may be mailed to the Commission and the Parties at the addresses below. Persons submitting a comment by mail must provide their name, address, and the Case Number under which they are commenting. Persons submitting a comment by mail also acknowledge that submitting a comment in an open case constitutes a public record under Idaho Code § 74-101(13), and all information provided by such person is available for public and media inspection.

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For the Idaho Public Utilities For the Company: Commission: Commission Secretary Anni Glogovac Idaho Public Utilities Commission Patrick Ehrbar P.O. Box 83720 Avista Corporation Boise, ID 83720-0074 P.O. Box 3727 secretary@puc.idaho.gov 1411 E. Mission Avenue, MSC 27 Spokane, WA 99220 anni.glogovac@avistacorp.com patrick.ehrbar avistacorp.com YOU ARE FURTHER NOTIFIED that the Company must file any reply comments by April 30, 2026. YOU ARE FURTHER NOTIFIED that if no written comments or protests are received within the time limit set, the Commission will consider this matter on its merits and enter its final order without a formal hearing. If written comments are received within the time limit set, the Commission will consider them and, in its discretion, may set the same for formal hearing. ORDER IT IS HEREBY ORDERED that this Application be processed under Modified Procedure, Rules 201-204, IDAPA 31.01.01.201-.204. Persons interested in submitting written comments must do so by April 23, 2026. The Company must file any reply comments by April 30, 2026. IT IS FURTHER ORDERED that parties comply with Order No. 35375, issued April 21,

1. Generally, all pleadings should be filed with the Commission electronically and will be deemed timely filed when received by the Commission Secretary. See Rule 14.02. Service between parties should continue to be accomplished electronically when possible. However, voluminous discovery-related documents may be filed and served on CD-ROM or a USB flash drive.

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DONE by Order of the Idaho Public Utilities Commission at Boise, Idaho this 30 day of th March, 2026. __________________________________________ EDWARD LODGE, PRESIDENT __________________________________________ JOHN R. HAMMOND JR., COMMISSIONER __________________________________________ DAYN HARDIE, COMMISSIONER ATTEST: Monica Barrios-Sanchez Commission Secretary

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