Exhibit 99.1 CENTURI & RIGGS DISTLER PRESENTATION JULY 2021 1Exhibit 99.1 CENTURI & RIGGS DISTLER PRESENTATION JULY 2021 1

DISCLOSURE This document contains statements which constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995 (“Reform Act”). All statements other than statements of historical fact included or incorporated by reference in this document are forward-looking statements, including, without limitation, statements regarding the Company’s plans, objectives, goals, intentions, projections, strategies, future events or performance, and underlying assumptions. The words “may,” “if,” “will,” “should,” “could,” “expect,” “plan,” “anticipate,” “believe,” “estimate,” “predict,” “project,” “continue,” “forecast,” “intend,” “promote,” “seek,” and similar words and expressions are generally used and intended to identify forward-looking statements. For example, statements regarding operating margin patterns, customer growth, the composition of our customer base, seasonal patterns, payment of debt, interest savings, replacement market and new construction market, forecasted operating cash flows and results of operations, sufficiency of working capital and current credit facility, the Company’s views regarding its liquidity position, projected financial performance and contract renewals are forward-looking statements. All forward-looking statements are intended to be subject to the safe harbor protection provided by the Reform Act. A number of important factors affecting the business and financial results of the Company could cause actual results to differ materially from those stated in the forward-looking statements. These factors include, but are not limited to, customer growth rates, conditions in the construction market, the effects of regulation/deregulation, changes in capital requirements and funding, the impact of conditions in the capital markets on financing costs, changes in construction expenditures and financing, changes in operations and maintenance expenses, accounting changes, future liability claims, results of bid work, impacts of structural and management changes, construction expenses, differences between actual and originally expected outcomes of Centuri construction agreements, competition, and our ability to raise capital in external financings. In addition, the Company can provide no assurance that its discussions regarding certain trends relating to its financing and operating expenses will continue in future periods. All forward-looking statements in this document are made as of the date hereof, based on information available to the Company as of the date hereof, and the Company assumes no obligation to update or revise any of its forward- looking statements even if experience or future changes show that the indicated results or events will not be realized. We caution you not to unduly rely on any forward-looking statement(s). All financial figures and calculations reference Company provided documents and may not match the audited financials due to adjustments and the exclusion of certain subsidiaries. We use certain information in this presentation that has been obtained from third parties, including Riggs Distler & Company, Inc. While we believe this information to be accurate, we have not independently verified all such information. This presentation shall not be deemed an offer to sell, or a solicitation of an offer to purchase, any securities of Southwest Gas Holdings, Inc. or its subsidiaries. Certain non-GAAP measures are used in this presentation, including EBITDA. For definitions of such non-GAAP measures and reconciliations to the most comparable GAAP measure, see the Appendix to this presentation 2 2DISCLOSURE This document contains statements which constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995 (“Reform Act”). All statements other than statements of historical fact included or incorporated by reference in this document are forward-looking statements, including, without limitation, statements regarding the Company’s plans, objectives, goals, intentions, projections, strategies, future events or performance, and underlying assumptions. The words “may,” “if,” “will,” “should,” “could,” “expect,” “plan,” “anticipate,” “believe,” “estimate,” “predict,” “project,” “continue,” “forecast,” “intend,” “promote,” “seek,” and similar words and expressions are generally used and intended to identify forward-looking statements. For example, statements regarding operating margin patterns, customer growth, the composition of our customer base, seasonal patterns, payment of debt, interest savings, replacement market and new construction market, forecasted operating cash flows and results of operations, sufficiency of working capital and current credit facility, the Company’s views regarding its liquidity position, projected financial performance and contract renewals are forward-looking statements. All forward-looking statements are intended to be subject to the safe harbor protection provided by the Reform Act. A number of important factors affecting the business and financial results of the Company could cause actual results to differ materially from those stated in the forward-looking statements. These factors include, but are not limited to, customer growth rates, conditions in the construction market, the effects of regulation/deregulation, changes in capital requirements and funding, the impact of conditions in the capital markets on financing costs, changes in construction expenditures and financing, changes in operations and maintenance expenses, accounting changes, future liability claims, results of bid work, impacts of structural and management changes, construction expenses, differences between actual and originally expected outcomes of Centuri construction agreements, competition, and our ability to raise capital in external financings. In addition, the Company can provide no assurance that its discussions regarding certain trends relating to its financing and operating expenses will continue in future periods. All forward-looking statements in this document are made as of the date hereof, based on information available to the Company as of the date hereof, and the Company assumes no obligation to update or revise any of its forward- looking statements even if experience or future changes show that the indicated results or events will not be realized. We caution you not to unduly rely on any forward-looking statement(s). All financial figures and calculations reference Company provided documents and may not match the audited financials due to adjustments and the exclusion of certain subsidiaries. We use certain information in this presentation that has been obtained from third parties, including Riggs Distler & Company, Inc. While we believe this information to be accurate, we have not independently verified all such information. This presentation shall not be deemed an offer to sell, or a solicitation of an offer to purchase, any securities of Southwest Gas Holdings, Inc. or its subsidiaries. Certain non-GAAP measures are used in this presentation, including EBITDA. For definitions of such non-GAAP measures and reconciliations to the most comparable GAAP measure, see the Appendix to this presentation 2 2

EXECUTIVE SUMMARY » Centuri Group, Inc. (“Centuri” or the “Company”) is a comprehensive utility services enterprise dedicated to delivering a diverse array of solutions to North America’s gas and electric providers – The Company generated LTM 3/31/21 revenue and compliance EBITDA of $1,979 million and $233 million, respectively th » On June 28 , 2021, Centuri entered into a definitive agreement to acquire Riggs Distler & Company, Inc. (“Riggs”) for a total enterprise value of $855 million – Riggs, a union electric utility services contractor primarily focused in the Northeastern U.S., generated LTM 3/31/21 revenue and adjusted EBITDA of $458 million and $58 million, respectively – On a run-rate basis, Riggs generated $75 million of adjusted EBITDA (including 14 incremental Master Service Agreements (“MSAs”) awarded with two utility providers (who are existing customers), which are expected to contribute an incremental ~$17 million of EBITDA by year-end 2022) » The acquisition enhances Centuri’s scale, geographic footprint, service offerings and financial profile, while retaining its MSA-driven utility services profile with long- term contracts and multi-decade average customer tenure with high quality counterparties 1 – Pro forma for the acquisition, the combined company generated LTM 3/31/21 revenue and run-rate adjusted EBITDA of $2,437 million and $308 million , respectively; note that Centuri has not modeled any cost synergies for the acquisition due to minimal overlap in the businesses today » The acquisition is expected to close in August or September, subject to regulatory approvals 1 Includes $17 million of run-rate adjustments from 14 new MSAs with two existing utility customers expected to be fully realized by year-end 2022 3 3 Source: Riggs provided financials; Riggs audited financial statementsEXECUTIVE SUMMARY » Centuri Group, Inc. (“Centuri” or the “Company”) is a comprehensive utility services enterprise dedicated to delivering a diverse array of solutions to North America’s gas and electric providers – The Company generated LTM 3/31/21 revenue and compliance EBITDA of $1,979 million and $233 million, respectively th » On June 28 , 2021, Centuri entered into a definitive agreement to acquire Riggs Distler & Company, Inc. (“Riggs”) for a total enterprise value of $855 million – Riggs, a union electric utility services contractor primarily focused in the Northeastern U.S., generated LTM 3/31/21 revenue and adjusted EBITDA of $458 million and $58 million, respectively – On a run-rate basis, Riggs generated $75 million of adjusted EBITDA (including 14 incremental Master Service Agreements (“MSAs”) awarded with two utility providers (who are existing customers), which are expected to contribute an incremental ~$17 million of EBITDA by year-end 2022) » The acquisition enhances Centuri’s scale, geographic footprint, service offerings and financial profile, while retaining its MSA-driven utility services profile with long- term contracts and multi-decade average customer tenure with high quality counterparties 1 – Pro forma for the acquisition, the combined company generated LTM 3/31/21 revenue and run-rate adjusted EBITDA of $2,437 million and $308 million , respectively; note that Centuri has not modeled any cost synergies for the acquisition due to minimal overlap in the businesses today » The acquisition is expected to close in August or September, subject to regulatory approvals 1 Includes $17 million of run-rate adjustments from 14 new MSAs with two existing utility customers expected to be fully realized by year-end 2022 3 3 Source: Riggs provided financials; Riggs audited financial statements

CENTURI OVERVIEW 4 4CENTURI OVERVIEW 4 4

CENTURI OWNED BY INVESTMENT-GRADE RATED SWX » SWX is a holding company that owns all of the shares of common stock of Centuri and Southwest Gas Corporation (“Southwest Gas”) Baa2 / BBB+ / BBB+ » Centuri represents SWX’s “utility infrastructure services” segment, which comprised ~59% and ~32% of SWX revenue and net income, respectively, in 2020 Baa1 / A- / A- Gas Utility Group Electric Utility Group Canada Group 5 5 Source: Centuri management

COMPANY HISTORY 1967 1987 1996 2000 2014 2017 2018 2020 2021 NPL Phoenix Southwest Strategic Industry Record Riggs Strategic Alliances Neuco Acquisition Founded Move Gas Growth Leadership Achievements Acquisition NPL was founded in NPL becomes a wholly- With a focus on Strategic Alliances With a 100-year vision Centuri expands its Centuri is ranked #12 Company-wide Riggs acquisition Gonvick, Minnesota as owned subsidiary of national growth, NPL developed to meet the for growth and geographical reach in in ENR’s Top 600 record safety expands Centuri Northern Gas Line Southwest Gas relocates long term needs of key diversification, Centuri the U.S. to include New Specialty Contractors performance union electric utility Constructors Corporation, following its corporate customers Construction Group is England with the distribution services Centuri grows electric Annual revenue completion of a $24 Over fifty years later headquarters to established as a holding acquisition of and adds significant million acquisition T&D services and increases to $1.95 NPL is still serving its Phoenix, Arizona company and enters the New England Utility access to expands geographic billion very first customer, now Canadian market with Constructors, Inc. renewables and 5G reach into the U.S. Gulf Electric Utility known as Minnesota the acquisition of Link- (Neuco) Datacom Coast region with the Energy Resources segment exceeds Line Group of acquisition of Linetec (MERC) 20% of revenue Companies Services, LLC Revenue exceeds $1 billion in first full year of combined company (2015) 6 6 Source: Centuri managementCOMPANY HISTORY 1967 1987 1996 2000 2014 2017 2018 2020 2021 NPL Phoenix Southwest Strategic Industry Record Riggs Strategic Alliances Neuco Acquisition Founded Move Gas Growth Leadership Achievements Acquisition NPL was founded in NPL becomes a wholly- With a focus on Strategic Alliances With a 100-year vision Centuri expands its Centuri is ranked #12 Company-wide Riggs acquisition Gonvick, Minnesota as owned subsidiary of national growth, NPL developed to meet the for growth and geographical reach in in ENR’s Top 600 record safety expands Centuri Northern Gas Line Southwest Gas relocates long term needs of key diversification, Centuri the U.S. to include New Specialty Contractors performance union electric utility Constructors Corporation, following its corporate customers Construction Group is England with the distribution services Centuri grows electric Annual revenue completion of a $24 Over fifty years later headquarters to established as a holding acquisition of and adds significant million acquisition T&D services and increases to $1.95 NPL is still serving its Phoenix, Arizona company and enters the New England Utility access to expands geographic billion very first customer, now Canadian market with Constructors, Inc. renewables and 5G reach into the U.S. Gulf Electric Utility known as Minnesota the acquisition of Link- (Neuco) Datacom Coast region with the Energy Resources segment exceeds Line Group of acquisition of Linetec (MERC) 20% of revenue Companies Services, LLC Revenue exceeds $1 billion in first full year of combined company (2015) 6 6 Source: Centuri management

CENTURI AT A GLANCE Overview Work Type Breakdown 1 1 Revenue Gross Profit » Comprehensive utility services enterprise dedicated to delivering a diverse Other Utility Other Utility array of solutions, including replacement and installation work, to North Services Services America’s gas and electric providers 14% 16% Gas Utility » Headquartered in Phoenix, Arizona with more than 9,000 employees 51% serving primarily utility customers across the U.S. & Canada Electric Gas Utility Utility Electric 61% 23% Utility » 50+ year operating history with significant growth trajectory, particularly with 35% recent expansion into electric utilities Historical Revenue 1 » 77% of revenue from multi-year MSAs that drive stable, recurring revenue ($ in millions) – Heavily weighted toward unit price and time and materials contracts, $1,979 $1,948 $1,751 with limited fixed-price lump-sum bids $1,522 » Strong blue-chip customer base with primarily investment grade credit- rated, investor-owned utilities and municipalities 2018 2019 2020 LTM 3/31/21 » Operates in two key segments across the U.S. and Canada: Historical Compliance EBITDA & Margin – Gas Utility: provides installation, replacement and maintenance of gas ($ in millions) $233 distribution, local transmission, station and storage facilities $219 $178 – Electric Utility: provides transmission line, distribution line, substation $141 and storm restoration electric services 11.8% 11.2% 10.2% 11.2% 11.9% 9.3% 10.2% 2018 2019 2020 LTM 3/31/21 1 As of LTM 3/31/21 7 7 Source: Centuri management; Centuri financial statementsCENTURI AT A GLANCE Overview Work Type Breakdown 1 1 Revenue Gross Profit » Comprehensive utility services enterprise dedicated to delivering a diverse Other Utility Other Utility array of solutions, including replacement and installation work, to North Services Services America’s gas and electric providers 14% 16% Gas Utility » Headquartered in Phoenix, Arizona with more than 9,000 employees 51% serving primarily utility customers across the U.S. & Canada Electric Gas Utility Utility Electric 61% 23% Utility » 50+ year operating history with significant growth trajectory, particularly with 35% recent expansion into electric utilities Historical Revenue 1 » 77% of revenue from multi-year MSAs that drive stable, recurring revenue ($ in millions) – Heavily weighted toward unit price and time and materials contracts, $1,979 $1,948 $1,751 with limited fixed-price lump-sum bids $1,522 » Strong blue-chip customer base with primarily investment grade credit- rated, investor-owned utilities and municipalities 2018 2019 2020 LTM 3/31/21 » Operates in two key segments across the U.S. and Canada: Historical Compliance EBITDA & Margin – Gas Utility: provides installation, replacement and maintenance of gas ($ in millions) $233 distribution, local transmission, station and storage facilities $219 $178 – Electric Utility: provides transmission line, distribution line, substation $141 and storm restoration electric services 11.8% 11.2% 10.2% 11.2% 11.9% 9.3% 10.2% 2018 2019 2020 LTM 3/31/21 1 As of LTM 3/31/21 7 7 Source: Centuri management; Centuri financial statements

COMPANY OVERVIEW Gas Utility Business Headquarters Phoenix, Arizona Lawrence, Massachusetts Salt Lake City, Utah Year Founded 1967 1972 2016 » Distribution and urban pipeline construction » Distribution and urban pipeline construction » Urban pipeline construction Primary Services » Pipeline integrity management » Trenchless technology » Pipeline integrity management » Station and facility construction » Regulated gas utilities » Regulated gas utilities » Regulated gas utilities Key End Market » Regulated combo utilities » Regulated combo utilities » Regulated combo utilities Geography » Throughout the U.S. » Massachusetts, New Hampshire, Maine » Utah, Nevada, Arizona Select Customers Bid Bid Bid 7% 26% 9% 1 Contract Type MSA MSA MSA 74% 91% 93% Employees ~4,500 ~300 ~225 Union Workforce Yes No No 1 As of LTM 3/31/21 8 8 Source: Centuri managementCOMPANY OVERVIEW Gas Utility Business Headquarters Phoenix, Arizona Lawrence, Massachusetts Salt Lake City, Utah Year Founded 1967 1972 2016 » Distribution and urban pipeline construction » Distribution and urban pipeline construction » Urban pipeline construction Primary Services » Pipeline integrity management » Trenchless technology » Pipeline integrity management » Station and facility construction » Regulated gas utilities » Regulated gas utilities » Regulated gas utilities Key End Market » Regulated combo utilities » Regulated combo utilities » Regulated combo utilities Geography » Throughout the U.S. » Massachusetts, New Hampshire, Maine » Utah, Nevada, Arizona Select Customers Bid Bid Bid 7% 26% 9% 1 Contract Type MSA MSA MSA 74% 91% 93% Employees ~4,500 ~300 ~225 Union Workforce Yes No No 1 As of LTM 3/31/21 8 8 Source: Centuri management

COMPANY OVERVIEW (CONT’D) Electric Utility Canada Group Business Headquarters Alexandria, Louisiana Phoenix, Arizona Vaughan, Ontario Cambridge, Ontario Year Founded 2014 2019 1994 1996 » Distribution and urban pipeline construction » Utility pole wire maintenance » Pipeline integrity management Primary Services » Transmission and distribution line construction » Telecommunication & electric underground construction & fabrication » Emergency electrical services restoration » Fabrication, gas pipeline, civil and industrial » Airport fueling systems Key End Market » Large investor-owned utilities (electric and combo) and municipalities » Primarily regulated gas utilities Geography » Throughout the Southeast, Southwest and Gulf Coast » Alberta, British Columbia and Ontario Select Customers Bid Bid 28% 19% 1 Contract Type MSA 72% MSA 81% Employees ~1,500 ~750 Union Workforce No (Linetec) / Yes (National Powerline) Yes 1 As of LTM 3/31/21 9 9 Source: Centuri managementCOMPANY OVERVIEW (CONT’D) Electric Utility Canada Group Business Headquarters Alexandria, Louisiana Phoenix, Arizona Vaughan, Ontario Cambridge, Ontario Year Founded 2014 2019 1994 1996 » Distribution and urban pipeline construction » Utility pole wire maintenance » Pipeline integrity management Primary Services » Transmission and distribution line construction » Telecommunication & electric underground construction & fabrication » Emergency electrical services restoration » Fabrication, gas pipeline, civil and industrial » Airport fueling systems Key End Market » Large investor-owned utilities (electric and combo) and municipalities » Primarily regulated gas utilities Geography » Throughout the Southeast, Southwest and Gulf Coast » Alberta, British Columbia and Ontario Select Customers Bid Bid 28% 19% 1 Contract Type MSA 72% MSA 81% Employees ~1,500 ~750 Union Workforce No (Linetec) / Yes (National Powerline) Yes 1 As of LTM 3/31/21 9 9 Source: Centuri management

BROAD EXISTING GEOGRAPHIC FOOTPRINT Centuri’s Significant North American Presence Across Key Business Units l Centuri Corporate Headquarters » Operations in 55 primary locations across 40 states and >9,000 l Canyon Pipeline provinces in the U.S. and Canada employees supporting l Linetec Services North American gas – 37 U.S. States l Neuco and electric utilities at l NPL – 3 Canadian Provinces peak season l NPL Canada l National Powerline » Over 1,000 active crews and over 9,000 employees at peak l WSN Construction season that are geographically dispersed by business unit Gas Utility Electric Utility Canada Group Existing Centuri Footprint 10 10 Source: Centuri managementBROAD EXISTING GEOGRAPHIC FOOTPRINT Centuri’s Significant North American Presence Across Key Business Units l Centuri Corporate Headquarters » Operations in 55 primary locations across 40 states and >9,000 l Canyon Pipeline provinces in the U.S. and Canada employees supporting l Linetec Services North American gas – 37 U.S. States l Neuco and electric utilities at l NPL – 3 Canadian Provinces peak season l NPL Canada l National Powerline » Over 1,000 active crews and over 9,000 employees at peak l WSN Construction season that are geographically dispersed by business unit Gas Utility Electric Utility Canada Group Existing Centuri Footprint 10 10 Source: Centuri management

DIVERSE, BLUE-CHIP CUSTOMERS 1 Top 20 Customers Revenue Relationship Contract Customer # Credit Rating Revenue as % of Total ($ in Millions) Length (Yrs) Length (Yrs) 1 A2/A $233 43 5 12% 6% 2 Baa1/A- 126 36 4 18% 2 6% 3 Baa1/A- 112 25 7 24% 6% 4 A2/A 111 19 5 30% 6% 5 Baa2/BBB+ 111 7 3 Top 5 35% 5% 6 A2/A- 103 17 5 40% 7 A3/BBB+ 5% 92 14 6 45% 5% 8 A3/A- 91 26 12 50% 9 Baa2/A- 4% 88 4 3 54% 10 Baa2/BBB+ 4% 85 44 3 Top 10 58% 3% 11 Baa2/BBB+ 65 13 8 62% 12 A3/A 3% 57 26 10 64% 13 Baa2/A- 3% 53 21 5 67% 14 Baa2/BBB+ 3% 52 4 4 70% 15 A3/BBB+ 2% 45 32 8 Top 15 72% 2 16 A2/A- 2% 37 53 7 74% 17 A2/A- 2% 36 5 3 76% 18 Baa1/BBB+ 2% 31 5 2 77% 19 A2/A- 2% 31 29 5 79% 2% 20 Baa1/A- 29 25 7 80% Top 20 Total – Average $1,588 22 6 1 As of LTM 3/31/21 2 11 Denotes Parent Company Rating; Opco customer unrated 11 Source: Centuri managementDIVERSE, BLUE-CHIP CUSTOMERS 1 Top 20 Customers Revenue Relationship Contract Customer # Credit Rating Revenue as % of Total ($ in Millions) Length (Yrs) Length (Yrs) 1 A2/A $233 43 5 12% 6% 2 Baa1/A- 126 36 4 18% 2 6% 3 Baa1/A- 112 25 7 24% 6% 4 A2/A 111 19 5 30% 6% 5 Baa2/BBB+ 111 7 3 Top 5 35% 5% 6 A2/A- 103 17 5 40% 7 A3/BBB+ 5% 92 14 6 45% 5% 8 A3/A- 91 26 12 50% 9 Baa2/A- 4% 88 4 3 54% 10 Baa2/BBB+ 4% 85 44 3 Top 10 58% 3% 11 Baa2/BBB+ 65 13 8 62% 12 A3/A 3% 57 26 10 64% 13 Baa2/A- 3% 53 21 5 67% 14 Baa2/BBB+ 3% 52 4 4 70% 15 A3/BBB+ 2% 45 32 8 Top 15 72% 2 16 A2/A- 2% 37 53 7 74% 17 A2/A- 2% 36 5 3 76% 18 Baa1/BBB+ 2% 31 5 2 77% 19 A2/A- 2% 31 29 5 79% 2% 20 Baa1/A- 29 25 7 80% Top 20 Total – Average $1,588 22 6 1 As of LTM 3/31/21 2 11 Denotes Parent Company Rating; Opco customer unrated 11 Source: Centuri management

DIVERSE REVENUE STREAMS UNDERPINNED BY STABLE MSA AGREEMENTS Contract Overview Diverse Service Offerings… 1 Work Type » Centuri has two types of agreements with its customers: master service agreements (“MSAs”) and bid contracts Electric 23% – Under MSAs, customers issue work authorizations that describe the location, timing, and other details regarding a job; Gas New 9% each work authorization is generally a single performance obligation Pipeline Integrity – Generally bid contracts are performed for existing utility 7% customers Gas 1 Replacement Other Utility Services – ~77% of Centuri’s revenue is contracted under multi-year 52% 9% MSA agreements with extension options, providing recurring revenue and earnings stability …Anchored by Strong Contractual Agreements » MSA and bid contracts are structured as either fixed price, unit 1 1 price, or time and materials Contract Pricing Type Contract Structure Type – Fixed price: set amount received for entire project scope Unit Bid Price – Unit price: pre-set price for discrete units of work in contract 23% 68% – Time and materials: pre-determined per-hour rates for Fixed employees and other direct costs Price 8% 1 – ~92% of Centuri’s revenue is generated from time and materials or unit price contracts, driving margin stability and minimizing risk Time and MSA Materials 77% 24% 1 As of LTM 3/31/21; % of Revenue 12 12 Source: Centuri managementDIVERSE REVENUE STREAMS UNDERPINNED BY STABLE MSA AGREEMENTS Contract Overview Diverse Service Offerings… 1 Work Type » Centuri has two types of agreements with its customers: master service agreements (“MSAs”) and bid contracts Electric 23% – Under MSAs, customers issue work authorizations that describe the location, timing, and other details regarding a job; Gas New 9% each work authorization is generally a single performance obligation Pipeline Integrity – Generally bid contracts are performed for existing utility 7% customers Gas 1 Replacement Other Utility Services – ~77% of Centuri’s revenue is contracted under multi-year 52% 9% MSA agreements with extension options, providing recurring revenue and earnings stability …Anchored by Strong Contractual Agreements » MSA and bid contracts are structured as either fixed price, unit 1 1 price, or time and materials Contract Pricing Type Contract Structure Type – Fixed price: set amount received for entire project scope Unit Bid Price – Unit price: pre-set price for discrete units of work in contract 23% 68% – Time and materials: pre-determined per-hour rates for Fixed employees and other direct costs Price 8% 1 – ~92% of Centuri’s revenue is generated from time and materials or unit price contracts, driving margin stability and minimizing risk Time and MSA Materials 77% 24% 1 As of LTM 3/31/21; % of Revenue 12 12 Source: Centuri management

PROVEN BUSINESS STRATEGY AND TRACK RECORD OF SUCCESSFUL ACQUISITION INTEGRATIONS » Acquisition strategy has allowed Centuri to diversify its utility services platform and expand its geographic footprint » Disciplined and targeted approach to evaluating opportunities, including strategic fit and synergy opportunities » SWX has been supportive of Centuri’s acquisition strategy, providing meaningful contributions in connection with acquisition financing – SWX commitment to cover the remaining 20% equity buyout of Linetec from 2022-2024; redeemable non-controlling interest fair value of $205 million recorded at 3/31/21 Acquisition History Business Purchase Price Key Features & Achievements » Expansion into Canadian market 2014 1 $205 million » Added Canada’s 3 largest gas utilities as customers f/k/a Link-Line Group of Companies » Expansion into New England » Entry into non-union gas market $100 million 2017 » Cumulative net cash returned through 2020 equals ~80% of purchase price » Expansion into Southeastern U.S. » Entry into non-union electric market 2 $379 million 2018 » Significant equity contribution from SWX » Doubled size of business in first 25 months of ownership » Expansion into Northeast and Mid-Atlantic » Expansion within union electric market $855 million 2021 » Expansion into 5G Datacom and renewables end markets » Enhanced ESG profile 1 $191 million of cash paid at close along with seller retained equity 2 13 $303 million funded at close for 80% equity stake; remaining 20% to be purchased from 2022-2024 13 Source: Centuri management

RIGGS DISTLER OVERVIEW 14 14RIGGS DISTLER OVERVIEW 14 14

RIGGS AT A GLANCE 1 Overview Segment Breakdown Revenue Adjusted EBITDA » Leading utility services contractor (electric & gas) in the Mid-Atlantic and Northeast U.S. Other Other Infrastructure Infrastructure Services Services » Headquartered in Cherry Hill, NJ with ~1,500+ employees 35% 21% Utility » 110+ year operating history with significant recent growth due to 16 Utility Segment Segment newly awarded incremental MSAs (including 14 with two existing utility 65% 79% customers) Historical Revenue 2 » 86% of revenue derived from multi-year MSAs ($ in millions) $458 $440 – Approximately 120 MSAs including key client relationships with Exelon, Avangrid, National Grid and PSE&G $401 $383 – Long-standing relationships with top customers, with no customer 1 representing more than 13% of revenue 2018 2019 2020 LTM 3/31/21 » Operates in two reportable segments: Historical Adjusted EBITDA & Margin – Utility Segment: provides overhead and underground electric ($ in millions) distribution services, overhead electric transmission, substation, gas $58 $55 distribution and 5G Datacom services $41 $41 – Other Infrastructure Services Segment: provides mechanical, 12.6% 12.8% electrical and heavy civil services to a variety of customers including 10.6% 10.3% heavy industrial, renewable, utility & generation and government 2018 2019 2020 LTM 3/31/21 1 As of FY2020 2 As of LTM 3/31/21 15 15 Source: Riggs provided financials; Riggs audited financial statementsRIGGS AT A GLANCE 1 Overview Segment Breakdown Revenue Adjusted EBITDA » Leading utility services contractor (electric & gas) in the Mid-Atlantic and Northeast U.S. Other Other Infrastructure Infrastructure Services Services » Headquartered in Cherry Hill, NJ with ~1,500+ employees 35% 21% Utility » 110+ year operating history with significant recent growth due to 16 Utility Segment Segment newly awarded incremental MSAs (including 14 with two existing utility 65% 79% customers) Historical Revenue 2 » 86% of revenue derived from multi-year MSAs ($ in millions) $458 $440 – Approximately 120 MSAs including key client relationships with Exelon, Avangrid, National Grid and PSE&G $401 $383 – Long-standing relationships with top customers, with no customer 1 representing more than 13% of revenue 2018 2019 2020 LTM 3/31/21 » Operates in two reportable segments: Historical Adjusted EBITDA & Margin – Utility Segment: provides overhead and underground electric ($ in millions) distribution services, overhead electric transmission, substation, gas $58 $55 distribution and 5G Datacom services $41 $41 – Other Infrastructure Services Segment: provides mechanical, 12.6% 12.8% electrical and heavy civil services to a variety of customers including 10.6% 10.3% heavy industrial, renewable, utility & generation and government 2018 2019 2020 LTM 3/31/21 1 As of FY2020 2 As of LTM 3/31/21 15 15 Source: Riggs provided financials; Riggs audited financial statements

MARKET LEADER IN NORTHEAST & MID-ATLANTIC Riggs By the Numbers Geographic Footprint 20 200+ Riggs Location States Annual Current Riggs Market Served Customers Expansion Opportunity 1 Riggs Storm Work Coverage ~120 19 Customer Company MSAs Facilities 1,200+ 800+ >1,500 employees Company Operating Vehicles Equipment Units 1 Out-of-system storm work accounted for less than 1% of revenue in 2020 and ~2.5% on average from 2018-2020 16 16 Source: Riggs provided financials and informationMARKET LEADER IN NORTHEAST & MID-ATLANTIC Riggs By the Numbers Geographic Footprint 20 200+ Riggs Location States Annual Current Riggs Market Served Customers Expansion Opportunity 1 Riggs Storm Work Coverage ~120 19 Customer Company MSAs Facilities 1,200+ 800+ >1,500 employees Company Operating Vehicles Equipment Units 1 Out-of-system storm work accounted for less than 1% of revenue in 2020 and ~2.5% on average from 2018-2020 16 16 Source: Riggs provided financials and information

ABILITY TO SERVE THE ENTIRE UTILITY AND INFRASTRUCTURE VALUE CHAIN Turnkey capabilities equip Riggs to serve as a one-stop shop for customers, resulting in revenue opportunities across the utility and infrastructure landscape Unique Ability to Serve All Customer Needs Why it Matters to Customers » Platform supports transmission, distribution, substation, conventional and renewable » Consolidate spend with a single, trusted provider generation, 5G datacom and other infrastructure services » Single provider streamlines project delivery and reduces costs by eliminating layers of » Riggs primarily self-performs all work, which eliminates the need for subcontractors, markup and duplicative indirect costs optimizes scheduling, reduces costs and improves quality » Self-performing work ensures consistent execution, quality and accountability » Skilled union workforce and extensive footprint enable rapid response for normal-course and emergent work Processing Plant Industrial Infrastructure Telecom Storage Small Cell Installation Regulators/Meters and Maintenance Electrical Infrastructure Power Station Distribution Automation Services Generation Renewables Distribution Infrastructure Transmission Step-Up Substation Substation Transformers Solar Panel Installation EV Infrastructure Battery Storage Comprehensive service Offshore Wind Capabilities cover the entire Utility and Infrastructure Value chain Keeping Critical Infrastructure Operating at Peak Performance 17 17 Source: Riggs provided financials and informationABILITY TO SERVE THE ENTIRE UTILITY AND INFRASTRUCTURE VALUE CHAIN Turnkey capabilities equip Riggs to serve as a one-stop shop for customers, resulting in revenue opportunities across the utility and infrastructure landscape Unique Ability to Serve All Customer Needs Why it Matters to Customers » Platform supports transmission, distribution, substation, conventional and renewable » Consolidate spend with a single, trusted provider generation, 5G datacom and other infrastructure services » Single provider streamlines project delivery and reduces costs by eliminating layers of » Riggs primarily self-performs all work, which eliminates the need for subcontractors, markup and duplicative indirect costs optimizes scheduling, reduces costs and improves quality » Self-performing work ensures consistent execution, quality and accountability » Skilled union workforce and extensive footprint enable rapid response for normal-course and emergent work Processing Plant Industrial Infrastructure Telecom Storage Small Cell Installation Regulators/Meters and Maintenance Electrical Infrastructure Power Station Distribution Automation Services Generation Renewables Distribution Infrastructure Transmission Step-Up Substation Substation Transformers Solar Panel Installation EV Infrastructure Battery Storage Comprehensive service Offshore Wind Capabilities cover the entire Utility and Infrastructure Value chain Keeping Critical Infrastructure Operating at Peak Performance 17 17 Source: Riggs provided financials and information

LONG-STANDING RELATIONSHIPS WITH BLUE-CHIP CUSTOMERS » Average relationships with top utility customers of over 30 years » Complementary to Centuri’s 22-year average tenure for top 20 customers No overlap between Riggs’ top 10 » Extensive relationship and long-term contracts with major investor-owned utilities in the Mid-Atlantic and Northeast U.S. customers and Centuri’s 1 top 20 customers » Largest customer accounts for 13% of revenue, with no other single customer accounting for > 10% of revenue » Many customer relationships have multiple discrete MSAs, which are highly sticky contracts 1 Customer Credit Rating MSAs Utility Other Current Services % of Revenue √ 1 A2/BBB+ 6 OHD, UGD, Substation, Gas, Civil, Electrical 13% √ 2 Baa1/A- 5 OHD, UGD, OHT, Matting, Substation 9% √ 3 Baa1/A- 4 OHD, OHT, Matting, Gas 6% √ 4 Baa2/A- 2 Gas 6% 5 A3/A 5√√ OHD, UGD, OHT, Matting, Gas, Civil, Electrical 5% √ 6 A2/A - Electrical, Mechanical, Civil 4% 7 Baa2/BBB+ 3√ OHD, OHT, Matting 5% √ 8 Baa1/A- 3 OHD, OHT, Substation 3% 2 √ 9 A3/A- - Electrical 3% √ 10 A3/A- 5 Mechanical, Electrical, Civil 3% Total 57% 1 As of FY2020 2 Denotes Parent Company Rating; Opco customer unrated 18 18 Source: Riggs provided financials and informationLONG-STANDING RELATIONSHIPS WITH BLUE-CHIP CUSTOMERS » Average relationships with top utility customers of over 30 years » Complementary to Centuri’s 22-year average tenure for top 20 customers No overlap between Riggs’ top 10 » Extensive relationship and long-term contracts with major investor-owned utilities in the Mid-Atlantic and Northeast U.S. customers and Centuri’s 1 top 20 customers » Largest customer accounts for 13% of revenue, with no other single customer accounting for > 10% of revenue » Many customer relationships have multiple discrete MSAs, which are highly sticky contracts 1 Customer Credit Rating MSAs Utility Other Current Services % of Revenue √ 1 A2/BBB+ 6 OHD, UGD, Substation, Gas, Civil, Electrical 13% √ 2 Baa1/A- 5 OHD, UGD, OHT, Matting, Substation 9% √ 3 Baa1/A- 4 OHD, OHT, Matting, Gas 6% √ 4 Baa2/A- 2 Gas 6% 5 A3/A 5√√ OHD, UGD, OHT, Matting, Gas, Civil, Electrical 5% √ 6 A2/A - Electrical, Mechanical, Civil 4% 7 Baa2/BBB+ 3√ OHD, OHT, Matting 5% √ 8 Baa1/A- 3 OHD, OHT, Substation 3% 2 √ 9 A3/A- - Electrical 3% √ 10 A3/A- 5 Mechanical, Electrical, Civil 3% Total 57% 1 As of FY2020 2 Denotes Parent Company Rating; Opco customer unrated 18 18 Source: Riggs provided financials and information

HIGHLY RECURRING REVENUE UNDERPINNED BY LONG-TERM MSAs AND STABLE CONTRACTS » Riggs has 60 unique utility MSAs and 59 non-utility MSAs across multiple geographies − Annual volumes consistent given steady rate base driven nature of utility spending programs − Work across both segments is predominantly small ticket, short in duration and driven by ongoing maintenance requirements − The percentage of revenue generated from MSAs is expected to increase through 2022 onwards driven by ramp up of newly won MSAs and expected utility revenue synergies » While Riggs maintains a component of fixed price work it is able to maintain stability and predictability of cash flows by: − Performing primarily recurring maintenance oriented work under short-term and small-dollar jobs − Predominantly working with established customers; ~80% of fixed price done under MSA contracts and over 60% with utility customers 1 1 Utility MSA Count Contract Structure Type Contract Pricing Type 60 Bid 14% 44 Fixed 42 Price 39% T&M and Unit Price 61% MSA 3/31/21 86% 2019 2020 LTM 3/31 1 As of LTM 3/31/21; based on % of revenue 19 19 Source: Riggs provided financials and information

CENTURI INTENDS TO RETAIN KEY MEMBERS OF RIGGS MANAGEMENT » Post acquisition, the Riggs management team will continue to manage the Riggs business as a standalone operating company » Similar to the Neuco and Linetec acquisitions, Centuri intends to retain key members of management via multi-year employment agreements, signing bonuses and earn-up incentive programs » Riggs’ management team averages approximately 23 years of industry experience, with CEO Steve Zemaitatis, Jr. having a 20+ year tenure with Riggs Executives Riggs Tenure Industry Tenure Executives Riggs Tenure Industry Tenure Steve Zemaitatis, Jr. Kenneth Mckay 22 years 22 years 5 years 15 years President & CEO VP General Counsel Albert Fosbenner William Fischer 2 years 25 years 5 years 20 years CFO VP Heavy Industrial Craig Zemaitatis Craig Belfato 15 years 16 years 2 years 20 years VP Overhead Distribution VP Mechanical Manfred Konrath Paul Creedon 37 years 37 years 5 years 25 years VP Underground Distribution VP Civil Scott Zemaitatis Jason McKay 17 years 19 years 4 years 21 years VP Transmission Chief Information Officer Scott Donadio Richard Neill 4 years 22 years 3 years 28 years VP Gas Distribution Senior Director of EHS Chris Johnston Joseph Mason 3 years 24 years 9 years 24 years VP Electrical & Substation Corporate Fleet Manager Average ~10 years ~23 years 20 20 Source: Centuri & Riggs ManagementCENTURI INTENDS TO RETAIN KEY MEMBERS OF RIGGS MANAGEMENT » Post acquisition, the Riggs management team will continue to manage the Riggs business as a standalone operating company » Similar to the Neuco and Linetec acquisitions, Centuri intends to retain key members of management via multi-year employment agreements, signing bonuses and earn-up incentive programs » Riggs’ management team averages approximately 23 years of industry experience, with CEO Steve Zemaitatis, Jr. having a 20+ year tenure with Riggs Executives Riggs Tenure Industry Tenure Executives Riggs Tenure Industry Tenure Steve Zemaitatis, Jr. Kenneth Mckay 22 years 22 years 5 years 15 years President & CEO VP General Counsel Albert Fosbenner William Fischer 2 years 25 years 5 years 20 years CFO VP Heavy Industrial Craig Zemaitatis Craig Belfato 15 years 16 years 2 years 20 years VP Overhead Distribution VP Mechanical Manfred Konrath Paul Creedon 37 years 37 years 5 years 25 years VP Underground Distribution VP Civil Scott Zemaitatis Jason McKay 17 years 19 years 4 years 21 years VP Transmission Chief Information Officer Scott Donadio Richard Neill 4 years 22 years 3 years 28 years VP Gas Distribution Senior Director of EHS Chris Johnston Joseph Mason 3 years 24 years 9 years 24 years VP Electrical & Substation Corporate Fleet Manager Average ~10 years ~23 years 20 20 Source: Centuri & Riggs Management

ACQUISITION RATIONALE 21 21ACQUISITION RATIONALE 21 21

RIGGS IS THE PERFECT FIT FOR CENTURI… Combining our existing industry-leading utility services platform with a scaled, union electric utility distribution focused provider A Perfect Complementary Fit A Balanced Service Provider » Enhances electric utility distribution service capabilities, with ability to cater to union and nonunion markets Nonunion » Access to attractive service adjacencies with outsized Union Gas Gas growth prospects in electrification, 5G and renewables Utility Utility » Complementary footprint with scale in a new attractive geography » Strong cultural alignment with shared focus on safety Union Electric Nonunion » World-class management teams bringing together Utility Electric Utility expanded relationships and best practices » Retains low-risk, recurring, MSA-driven utility distribution services profile 22 22 Source: Centuri managementRIGGS IS THE PERFECT FIT FOR CENTURI… Combining our existing industry-leading utility services platform with a scaled, union electric utility distribution focused provider A Perfect Complementary Fit A Balanced Service Provider » Enhances electric utility distribution service capabilities, with ability to cater to union and nonunion markets Nonunion » Access to attractive service adjacencies with outsized Union Gas Gas growth prospects in electrification, 5G and renewables Utility Utility » Complementary footprint with scale in a new attractive geography » Strong cultural alignment with shared focus on safety Union Electric Nonunion » World-class management teams bringing together Utility Electric Utility expanded relationships and best practices » Retains low-risk, recurring, MSA-driven utility distribution services profile 22 22 Source: Centuri management

…COMPLEMENTS CENTURI’S EXISTING BUSINESS… Centuri Riggs » Utility services enterprise dedicated to delivering a diverse and » Utility infrastructure services contractor with a primary focus on Business Overview comprehensive array of solutions to North America’s gas and electric union electric and secondary work in gas distribution and power providers generation, including renewables and industrial services Geographic » 55 primary locations across 37 states and 3 provinces in the U.S. » 19 company facilities serving 20 states with a focused presence in Footprint and Canada, respectively the Northeast and Mid-Atlantic » Revenue: $1,979 million » Revenue: $458 million Financial Summary (LTM 3/31/21) » Compliance EBITDA: $233 million (~12% margin) » Adj. EBITDA: $58 million (~13% margin) Other Utility Gas Utility Services 11% Other Utility 16% Services 23% Utility Service 1 Revenue Mix 5G Datacom Gas Utility Electric Utility 4% 61% 23% Electric Utility Industrial 50% 12% MSA Revenue 75%+ 85%+ 2 Contribution 1 Riggs utility service revenue mix as of FY2020 and Centuri as of LTM 3/31/21 2 As of LTM 3/31/21 23 23 Source: Centuri management & Riggs historical financials…COMPLEMENTS CENTURI’S EXISTING BUSINESS… Centuri Riggs » Utility services enterprise dedicated to delivering a diverse and » Utility infrastructure services contractor with a primary focus on Business Overview comprehensive array of solutions to North America’s gas and electric union electric and secondary work in gas distribution and power providers generation, including renewables and industrial services Geographic » 55 primary locations across 37 states and 3 provinces in the U.S. » 19 company facilities serving 20 states with a focused presence in Footprint and Canada, respectively the Northeast and Mid-Atlantic » Revenue: $1,979 million » Revenue: $458 million Financial Summary (LTM 3/31/21) » Compliance EBITDA: $233 million (~12% margin) » Adj. EBITDA: $58 million (~13% margin) Other Utility Gas Utility Services 11% Other Utility 16% Services 23% Utility Service 1 Revenue Mix 5G Datacom Gas Utility Electric Utility 4% 61% 23% Electric Utility Industrial 50% 12% MSA Revenue 75%+ 85%+ 2 Contribution 1 Riggs utility service revenue mix as of FY2020 and Centuri as of LTM 3/31/21 2 As of LTM 3/31/21 23 23 Source: Centuri management & Riggs historical financials

…ENHANCES SCALE & DIVERSIFICATION… 1 2017 Centuri Transformation 2021E Pro Forma Centuri Addition of electric utility creates comprehensive pure- Business Units play utility distribution services platform Revenue $1,246 2x+ increase in revenue $2,500 ($ in millions) Adjusted EBITDA Margin ~8% ~340 bps margin expansion ~11% 2 3 Projected Growth Mid-Single Digit Attractive growth profile Double Digit 4 MSA as % of Revenue 71% Growing MSA orientation 78% Other Utility Services Other 17% 3% Gas Utility Gross Margin Increased access to electric 42% 4 by End Market utility distribution Gas Electric Utility Utility 97% 41% 1 Reflects 2021 estimated figures unless otherwise noted 2 2017-2019 CAGR 24 3 24 2021-2023 CAGR 4 Source: Centuri management Pro forma is LTM 3/31/21…ENHANCES SCALE & DIVERSIFICATION… 1 2017 Centuri Transformation 2021E Pro Forma Centuri Addition of electric utility creates comprehensive pure- Business Units play utility distribution services platform Revenue $1,246 2x+ increase in revenue $2,500 ($ in millions) Adjusted EBITDA Margin ~8% ~340 bps margin expansion ~11% 2 3 Projected Growth Mid-Single Digit Attractive growth profile Double Digit 4 MSA as % of Revenue 71% Growing MSA orientation 78% Other Utility Services Other 17% 3% Gas Utility Gross Margin Increased access to electric 42% 4 by End Market utility distribution Gas Electric Utility Utility 97% 41% 1 Reflects 2021 estimated figures unless otherwise noted 2 2017-2019 CAGR 24 3 24 2021-2023 CAGR 4 Source: Centuri management Pro forma is LTM 3/31/21

…ADDS ESG OPPORTUNITIES… » Provides real ESG market messaging opportunity for SWX and Centuri with renewable projects Riggs has accomplished so far » Riggs has experience building several of the renewable opportunities Centuri has been assessing – Solar Projects – Anaerobic Digester Facilities – Battery Storage – EV Charging – Fuel Cells – Microgrid » Increases pipeline replacement capabilities which dramatically reduce methane emissions through system modernization and leak repair » Participation in Offshore Wind (“OSW”) projects when finally realized » Riggs resume improves overall SWX ESG narrative Diversity, 100+ Years of Tracking & Reducing Renewables and Clean Power Services Offshore Wind Community Equity and Direct Carbon Emissions Enabling GHG Savings and Resiliency Services Safety Inclusion A leading experienced partner to utilities in: Positioned to support Adopting Centuri Established community Proven safety culture EV Charging Battery expected wave of U.S. off- partner program and GHG Reduction Goal and excellent safety Fuel Cells shore wind projects critical employee “Helping Infrastructure Storage track record over Hands” philanthropic to decarbonizing coastal 100+ year history Smart Meters RNG Microgrids initiative population centers 25 25 Source: Centuri management…ADDS ESG OPPORTUNITIES… » Provides real ESG market messaging opportunity for SWX and Centuri with renewable projects Riggs has accomplished so far » Riggs has experience building several of the renewable opportunities Centuri has been assessing – Solar Projects – Anaerobic Digester Facilities – Battery Storage – EV Charging – Fuel Cells – Microgrid » Increases pipeline replacement capabilities which dramatically reduce methane emissions through system modernization and leak repair » Participation in Offshore Wind (“OSW”) projects when finally realized » Riggs resume improves overall SWX ESG narrative Diversity, 100+ Years of Tracking & Reducing Renewables and Clean Power Services Offshore Wind Community Equity and Direct Carbon Emissions Enabling GHG Savings and Resiliency Services Safety Inclusion A leading experienced partner to utilities in: Positioned to support Adopting Centuri Established community Proven safety culture EV Charging Battery expected wave of U.S. off- partner program and GHG Reduction Goal and excellent safety Fuel Cells shore wind projects critical employee “Helping Infrastructure Storage track record over Hands” philanthropic to decarbonizing coastal 100+ year history Smart Meters RNG Microgrids initiative population centers 25 25 Source: Centuri management

…AND REINFORCES CENTURI’S BUSINESS PROFILE Centuri + Riggs creates a premier diversified utility services company with balanced growth optionality Low Risk… …Drives Highest Growth and Least Volatility 1 1 Revenue by Contract Structure Revenue by Contract Type 2 3 Rank 10Y EBITDA CAGR 10Y EBITDA Volatility Bid Fixed Price 22% 14% Highest Least 1 growth volatile T&M and MSA Unit Price 78% 86% 2 …Plus Favorable Competitive Position… 3 Double-breasted workforce üüüüü Gas distribution services üüüüû No cross-country pipeline projects 4 üûûûü Electric distribution services üüüüü No cross-country electric transmission projects üûûûû 5 Enhanced ESG profile / Access to high-growth 5G üüüüü Denotes significantly increased capabilities from Riggs acquisition Denotes new capability from Riggs acquisition 1 Pro forma Centuri and Riggs; LTM as of 3/31/21 2 Compound Annual Growth Rate (CAGR) rankings based on change from 12/31/2010 to 12/31/2020 26 26 3 Volatility rankings based on Standard Error of the Regression (SER) statistics for 10 years ended 12/31/2020 Source: Centuri management

KEY CREDIT HIGHLIGHTS 27 27KEY CREDIT HIGHLIGHTS 27 27

KEY CREDIT HIGHLIGHTS 1 Leading Utility Services Company Consistent Free Cash Flow Generation 2 Commitment to a Conservative Credit Profile 3 4 Recurring and Stable Revenue from MSAs Blue Chip Customer Base with Longstanding Relationships 5 Favorable Industry Tailwinds 6 Highly Experienced Management Team 7 28 28KEY CREDIT HIGHLIGHTS 1 Leading Utility Services Company Consistent Free Cash Flow Generation 2 Commitment to a Conservative Credit Profile 3 4 Recurring and Stable Revenue from MSAs Blue Chip Customer Base with Longstanding Relationships 5 Favorable Industry Tailwinds 6 Highly Experienced Management Team 7 28 28

1 ENHANCED SCALE & DIVERSIFICATION… 1 $2,437 million of Revenue 1 $308 million of Adjusted EBITDA 2 Solidified North American Leader Diverse Earnings Composition End Market Geography Over 10,500 Top State Other Utility employees Services 15% supporting North 17% American gas All Other and electric Gas Utility 28% utilities at peak 42% season Electric Canada Utility 10% 41% Top 10 States 62% Customer Type Other 15% All Other 28% Utility Existing Centuri Footprint 85% Riggs Footprint 1 As of LTM 3/31/21; pro forma Centuri and Riggs; EBITDA includes $17 million of run-rate adjustments from 14 new MSAs with two existing utility customers expected to be fully realized by year-end 2022 29 2 29 As of LTM 3/31/21; Geography and Customer Type based on Revenue; End Market by Gross Profit Source: Centuri management1 ENHANCED SCALE & DIVERSIFICATION… 1 $2,437 million of Revenue 1 $308 million of Adjusted EBITDA 2 Solidified North American Leader Diverse Earnings Composition End Market Geography Over 10,500 Top State Other Utility employees Services 15% supporting North 17% American gas All Other and electric Gas Utility 28% utilities at peak 42% season Electric Canada Utility 10% 41% Top 10 States 62% Customer Type Other 15% All Other 28% Utility Existing Centuri Footprint 85% Riggs Footprint 1 As of LTM 3/31/21; pro forma Centuri and Riggs; EBITDA includes $17 million of run-rate adjustments from 14 new MSAs with two existing utility customers expected to be fully realized by year-end 2022 29 2 29 As of LTM 3/31/21; Geography and Customer Type based on Revenue; End Market by Gross Profit Source: Centuri management

1 …CREATES TOP PLAYER IN UTILITY SERVICES SECTOR 1 Top 10 Utility Services Firms ($ in millions) $5,502 $3,950 $1,620 $1,610 $1,547 $1,467 $731 $505 $350 Fourth largest utility services provider by total revenue 1 By 2019 Utility Revenue; includes Centuri + Riggs utility only pro forma FY 2019 revenue; MasTec pro forma for acquisition of Intren in May 2021 30 30 Source: ENR “The Top 600 Specialty Contractors”; October 2020; Company management 1 …CREATES TOP PLAYER IN UTILITY SERVICES SECTOR 1 Top 10 Utility Services Firms ($ in millions) $5,502 $3,950 $1,620 $1,610 $1,547 $1,467 $731 $505 $350 Fourth largest utility services provider by total revenue 1 By 2019 Utility Revenue; includes Centuri + Riggs utility only pro forma FY 2019 revenue; MasTec pro forma for acquisition of Intren in May 2021 30 30 Source: ENR “The Top 600 Specialty Contractors”; October 2020; Company management

2 CONSISTENT FREE CASH FLOW GENERATION » $400+ million of Free Cash Flow generation since 2018 » $100+ million in Free Cash Flow generation since 2018 » Key cash flow drivers: » Key cash flow drivers: – Stable, recurring revenue supported by majority MSA contract structure – Accelerated growth from recent MSA contract wins – Modest maintenance CapEx requirements, averaging ~2% of revenue – Modest maintenance CapEx requirements, averaging ~2% of revenue over the last 3 years over the last 3 years Allows Centuri to delever quickly and predictably following debt-financed acquisitions 1 Free Cash Flow and Free Cash Flow Conversion ($ in millions) ($ in millions) Free Cash Flow Free Cash Flow Conversion Free Cash Flow Free Cash Flow Conversion $50 $206 $48 $183 $34 $30 $123 $109 88% 86% 86% 84% 83% 77% 73% 69% 2018 2019 2020 LTM 3/31/21 2018 2019 2020 LTM 3/31/21 1 Free Cash flow defined as Compliance/Adjusted EBITDA – Maintenance Capex (as defined in the prior Credit Agreement for Centuri); Conversion defined as (FCF / Compliance/Adjusted EBITDA) 31 31 Source: Centuri & Riggs Financials2 CONSISTENT FREE CASH FLOW GENERATION » $400+ million of Free Cash Flow generation since 2018 » $100+ million in Free Cash Flow generation since 2018 » Key cash flow drivers: » Key cash flow drivers: – Stable, recurring revenue supported by majority MSA contract structure – Accelerated growth from recent MSA contract wins – Modest maintenance CapEx requirements, averaging ~2% of revenue – Modest maintenance CapEx requirements, averaging ~2% of revenue over the last 3 years over the last 3 years Allows Centuri to delever quickly and predictably following debt-financed acquisitions 1 Free Cash Flow and Free Cash Flow Conversion ($ in millions) ($ in millions) Free Cash Flow Free Cash Flow Conversion Free Cash Flow Free Cash Flow Conversion $50 $206 $48 $183 $34 $30 $123 $109 88% 86% 86% 84% 83% 77% 73% 69% 2018 2019 2020 LTM 3/31/21 2018 2019 2020 LTM 3/31/21 1 Free Cash flow defined as Compliance/Adjusted EBITDA – Maintenance Capex (as defined in the prior Credit Agreement for Centuri); Conversion defined as (FCF / Compliance/Adjusted EBITDA) 31 31 Source: Centuri & Riggs Financials

3 COMMITMENT TO CONSERVATIVE CREDIT PROFILE WITH PROVEN DE-LEVERAGING » Centuri has a demonstrated history of prudence and discipline when managing its balance sheet, despite being acquisitive » Significant cash flow generation has allowed Centuri to consistently and quickly delever below its total leverage target of 3.0x following acquisitions » Meaningful balance sheet support provided by parent equity contributions from SWX – SWX contributed $235 million in connection with the acquisition of an 80% stake in Linetec in 2018 – SWX commitment to cover the remaining 20% equity buyout of Linetec from 2022-2024; redeemable non-controlling interest fair value of $205 million as of 3/31/21 1 Net Leverage Over Time Riggs Acquisition SWX contributed $235 million or ~75% of Link-Line Neuco Acquisition Linetec Acquisition August 2021 upfront cash payment for 80% equity Acquisition November 2017 November 2018 stake, reducing leverage at close 4.1x October 2014 SWX commitment to cover the remaining 20% equity buyout of Linetec from 2022-2024 2.7x 1.9x 1.9x 1.7x 1.7x 1.5x 1.4x 2014 2015 2016 2017 2018 2019 2020 Pro Forma Q1'21 Peak leverage occurs in Q2 and Q3 due to working capital needs while trough occurs at year end 1 Defined as (Total Funded Debt – Unrestricted Cash & Equivalents) / LTM Pro Forma Compliance EBITDA (pro forma for the full 12-month impact of any acquisitions made during that fiscal year); 32 Please reference the Appendix for a reconciliation 32 Source: Centuri financials3 COMMITMENT TO CONSERVATIVE CREDIT PROFILE WITH PROVEN DE-LEVERAGING » Centuri has a demonstrated history of prudence and discipline when managing its balance sheet, despite being acquisitive » Significant cash flow generation has allowed Centuri to consistently and quickly delever below its total leverage target of 3.0x following acquisitions » Meaningful balance sheet support provided by parent equity contributions from SWX – SWX contributed $235 million in connection with the acquisition of an 80% stake in Linetec in 2018 – SWX commitment to cover the remaining 20% equity buyout of Linetec from 2022-2024; redeemable non-controlling interest fair value of $205 million as of 3/31/21 1 Net Leverage Over Time Riggs Acquisition SWX contributed $235 million or ~75% of Link-Line Neuco Acquisition Linetec Acquisition August 2021 upfront cash payment for 80% equity Acquisition November 2017 November 2018 stake, reducing leverage at close 4.1x October 2014 SWX commitment to cover the remaining 20% equity buyout of Linetec from 2022-2024 2.7x 1.9x 1.9x 1.7x 1.7x 1.5x 1.4x 2014 2015 2016 2017 2018 2019 2020 Pro Forma Q1'21 Peak leverage occurs in Q2 and Q3 due to working capital needs while trough occurs at year end 1 Defined as (Total Funded Debt – Unrestricted Cash & Equivalents) / LTM Pro Forma Compliance EBITDA (pro forma for the full 12-month impact of any acquisitions made during that fiscal year); 32 Please reference the Appendix for a reconciliation 32 Source: Centuri financials

4 HIGHLY VISIBLE, RECURRING REVENUE FROM CUSTOMER CONTRACTS 1 Growing Utility MSA Count ü Sticky, multi-year MSAs with 207 183 high renewal rates ensure 175 60 44 consistent volume and create 42 a stable revenue base 147 139 133 ü ~3-5% built-in price escalators in MSAs to drive continued 2019 2020 Pro Forma Riggs + Centuri 3/31/21 growth across existing Centuri Riggs contract base Favorable Contract Mix ü Growing MSA count, heavily 1 1 Contract Type Contract Structure weighted toward unit price Bid Fixed and time and materials 22% Price contracts that drive stable 14% margins ü No material contract losses T&M and Unit MSA Price 78% 86% 1 As of LTM 3/31/21; pro forma Centuri and Riggs 33 33 Source: Centuri and Riggs management provided information4 HIGHLY VISIBLE, RECURRING REVENUE FROM CUSTOMER CONTRACTS 1 Growing Utility MSA Count ü Sticky, multi-year MSAs with 207 183 high renewal rates ensure 175 60 44 consistent volume and create 42 a stable revenue base 147 139 133 ü ~3-5% built-in price escalators in MSAs to drive continued 2019 2020 Pro Forma Riggs + Centuri 3/31/21 growth across existing Centuri Riggs contract base Favorable Contract Mix ü Growing MSA count, heavily 1 1 Contract Type Contract Structure weighted toward unit price Bid Fixed and time and materials 22% Price contracts that drive stable 14% margins ü No material contract losses T&M and Unit MSA Price 78% 86% 1 As of LTM 3/31/21; pro forma Centuri and Riggs 33 33 Source: Centuri and Riggs management provided information

5 WELL-TENURED, BLUE-CHIP UTILITY CUSTOMER BASE Key Blue Chip Customers Key Statistics Gas Electric Combination ~25 Years Weighted Average Customer 1 Tenure ~5 Years Weighted 1 Average Contract Length Top Customer 10% All other 52% Top 10 Customers 48% Denotes new Centuri customers from Riggs acquisition 1 Based on top 20 customers as of LTM 3/31/21 34 34 Source: Centuri management5 WELL-TENURED, BLUE-CHIP UTILITY CUSTOMER BASE Key Blue Chip Customers Key Statistics Gas Electric Combination ~25 Years Weighted Average Customer 1 Tenure ~5 Years Weighted 1 Average Contract Length Top Customer 10% All other 52% Top 10 Customers 48% Denotes new Centuri customers from Riggs acquisition 1 Based on top 20 customers as of LTM 3/31/21 34 34 Source: Centuri management

6 FAVORABLE INDUSTRY TAILWINDS: AGING UTILITY INFRASTRUCTURE Strong tailwinds across utility distribution end markets support long-term growth Utility Distribution Outlook Electric Utility Distribution Gas Utility Distribution » Aging infrastructure will demand significant replacements and upgrades to » Aging natural gas distribution infrastructure has caused meaningful public maintain system performance health and safety risks, driving utilities to a multi-decade replacement cycle » Investment required to integrate renewable and distributed energy resources » This replacement cycle currently underway is regulatory-driven and has already been allocated funding » Increasing need for additional electricity generation to meet demand 1 Aging Electric Infrastructure Crumbling Gas Infrastructure 2 3 3 Electrical Distribution infrastructure age Investments in Distribution Infrastructure Gas Distribution Pipelines Constructed Construction Spend on Distribution ($ in billions) (By decade) ($ in billions) relative to useful lifespan Near end of useful life Distribution Capex Expenditures for new and replacement Pre-1940s 1940s 1950s 1960s 17 distribution mileage have experienced At end of useful life Distribution O&M strong growth regardless of 15 43 Within useful life Recession Resilience 13 1970s 1980s 1990s 2000s macroeconomic conditions 38 36 34 12 Recession Resilience 32 31 30 10 27 27 27 27 25 25 8 7 5%2%9% 15% 13% 16% 21% 19% 7 41% Distribution 6 5 5 16 5 5 5 15 14 Infrastructure 55% Nearly 45% of gas distribution infrastructure is near or at the end 4% of its useful life of 40 years 1 Department of Energy 2 Federal Energy Regulatory Commission 35 35 3 American Gas Association; expenses include spending on distribution

6 FAVORABLE INDUSTRY TAILWINDS: NEW HIGH-GROWTH INFRASTRUCTURE END MARKETS Strong tailwinds across related infrastructure end markets support long-term growth Wireless and Renewable Energy 5G Datacom Energy Transition » Small cell wireless density requires significant buildout, and existing utility » Renewable energy accounts for ~18% of U.S. energy mix and is projected 1 infrastructure will be a key component to densification to reach 31% by 2050 as utilities move away from fossil fuels » Utility infrastructure will require make-ready work to realign existing pole » Significant forthcoming buildout of renewable assets and supporting attachments to support 5G equipment infrastructure 2 3 Global Small Cell New Deployments by Environment Accelerating U.S. Capacity and Investment (Units in millions) (Units in gigawatts; $ in billions) 37 GW 10.3 Enterprise 8.9 Urban Operating Offshore Wind Capacity Residential and Rural 7.8 25 GW 7.2 166 Total Capital Investment 6.7 6.3 5.5 3.9 108 2.7 4 GW 2 GW 2 17 2017 2018 2019 2020 2021P 2022P 2023P 2024P 2025P 2020 2025P 2030P 2035P 1 U.S. Energy Information Administration 2 Small Cell Market Status Report – Small Cell Forum (December 2018) 36 36 3 Wood Mackenzie6 FAVORABLE INDUSTRY TAILWINDS: NEW HIGH-GROWTH INFRASTRUCTURE END MARKETS Strong tailwinds across related infrastructure end markets support long-term growth Wireless and Renewable Energy 5G Datacom Energy Transition » Small cell wireless density requires significant buildout, and existing utility » Renewable energy accounts for ~18% of U.S. energy mix and is projected 1 infrastructure will be a key component to densification to reach 31% by 2050 as utilities move away from fossil fuels » Utility infrastructure will require make-ready work to realign existing pole » Significant forthcoming buildout of renewable assets and supporting attachments to support 5G equipment infrastructure 2 3 Global Small Cell New Deployments by Environment Accelerating U.S. Capacity and Investment (Units in millions) (Units in gigawatts; $ in billions) 37 GW 10.3 Enterprise 8.9 Urban Operating Offshore Wind Capacity Residential and Rural 7.8 25 GW 7.2 166 Total Capital Investment 6.7 6.3 5.5 3.9 108 2.7 4 GW 2 GW 2 17 2017 2018 2019 2020 2021P 2022P 2023P 2024P 2025P 2020 2025P 2030P 2035P 1 U.S. Energy Information Administration 2 Small Cell Market Status Report – Small Cell Forum (December 2018) 36 36 3 Wood Mackenzie

7 HIGHLY EXPERIENCED MANAGEMENT TEAM Executive Leadership Paul Daily Kevin Neill Richard Delaney Rob Lyons Michael Cicchella, Jr. James Connell, Jr. Steve Adams President & Chief Executive Vice Executive Vice President, Centuri Executive Vice Executive Vice Senior Vice Executive Officer President, Chief President, Chief Power Group President, Chief President, Chief President, Centuri Financial Officer & Operating Officer Administrative Officer Customer Officer Power Group Treasurer » 35+ years of » 30+ years of experience » 34+ years of experience » 40+ years of experience » 20+ years of experience » 25+ years of experience » 35+ years of experience across across financial reporting, across operations and across operations and in utility services across various executive experience of senior leadership of accounting, investor management senior leadership of companies managing leadership roles driving operational leadership infrastructure relations and M&A experience leadership utility services M&A, IT, Safety, Fleet, customer and market across the electric T&D Experience engineering and companies Supply Chain and HR development industry (including » Joined Centuri in 2012 as » Joined Centuri in 2002 construction companies President of PAR CFO of NPL Construction as President & COO of » Joined Centuri in 2018 » Joined Centuri in 2016 » Joined Centuri in 2006 Electric, a >$1.6B NPL Canada as EVP of Electrical as SVP & CAO as Director of Supply » Joined Centuri in 2016 business) Transmission and Chain & Asset Mgmt. for as CEO Distribution NPL Construction » Joined Centuri in 2019 Prior Companies 37 Source: Centuri management 377 HIGHLY EXPERIENCED MANAGEMENT TEAM Executive Leadership Paul Daily Kevin Neill Richard Delaney Rob Lyons Michael Cicchella, Jr. James Connell, Jr. Steve Adams President & Chief Executive Vice Executive Vice President, Centuri Executive Vice Executive Vice Senior Vice Executive Officer President, Chief President, Chief Power Group President, Chief President, Chief President, Centuri Financial Officer & Operating Officer Administrative Officer Customer Officer Power Group Treasurer » 35+ years of » 30+ years of experience » 34+ years of experience » 40+ years of experience » 20+ years of experience » 25+ years of experience » 35+ years of experience across across financial reporting, across operations and across operations and in utility services across various executive experience of senior leadership of accounting, investor management senior leadership of companies managing leadership roles driving operational leadership infrastructure relations and M&A experience leadership utility services M&A, IT, Safety, Fleet, customer and market across the electric T&D Experience engineering and companies Supply Chain and HR development industry (including » Joined Centuri in 2012 as » Joined Centuri in 2002 construction companies President of PAR CFO of NPL Construction as President & COO of » Joined Centuri in 2018 » Joined Centuri in 2016 » Joined Centuri in 2006 Electric, a >$1.6B NPL Canada as EVP of Electrical as SVP & CAO as Director of Supply » Joined Centuri in 2016 business) Transmission and Chain & Asset Mgmt. for as CEO Distribution NPL Construction » Joined Centuri in 2019 Prior Companies 37 Source: Centuri management 37

HISTORICAL FINANCIAL SUMMARY 38 38HISTORICAL FINANCIAL SUMMARY 38 38

CENTURI HISTORICAL FINANCIAL PERFORMANCE Revenue Compliance EBITDA and Margin ($ in millions) $2,25(0 $ in millions) $1,979 $233 $1,948 $240 $219 $1,751 $1,522 $178 $1,500 $160 $141 12% 11% $750 $80 10% 9% $0 $0 2018 2019 2020 LTM 3/31/21 2018 2019 2020 LTM 3/31/21 Compliance EBITDA EBITDA Margin 1 1 Capital Expenditures FCF and FCF Conversion $200 ($ in millions) ($ in millions) $206 160% $200 $183 140% $144 $150 120% $125 $150 $120 $123 100% $55 $109 $36 $27 $100 80% $79 $100 88% 84% 60% 77% $32 69% $50 40% $50 $93 $89 $89 20% $47 $0 0% $0 2018 2019 2020 LTM 3/31/21 2018 2019 2020 LTM 3/31/21 FCF FCF Conversion Growth Capex Maintenance Capex 1 Free Cash flow defined as Compliance EBITDA – Maintenance Capex (as defined in the prior Credit Agreement); Conversion defined as (FCF / Compliance EBITDA) 39 39 Source: Centuri financialsCENTURI HISTORICAL FINANCIAL PERFORMANCE Revenue Compliance EBITDA and Margin ($ in millions) $2,25(0 $ in millions) $1,979 $233 $1,948 $240 $219 $1,751 $1,522 $178 $1,500 $160 $141 12% 11% $750 $80 10% 9% $0 $0 2018 2019 2020 LTM 3/31/21 2018 2019 2020 LTM 3/31/21 Compliance EBITDA EBITDA Margin 1 1 Capital Expenditures FCF and FCF Conversion $200 ($ in millions) ($ in millions) $206 160% $200 $183 140% $144 $150 120% $125 $150 $120 $123 100% $55 $109 $36 $27 $100 80% $79 $100 88% 84% 60% 77% $32 69% $50 40% $50 $93 $89 $89 20% $47 $0 0% $0 2018 2019 2020 LTM 3/31/21 2018 2019 2020 LTM 3/31/21 FCF FCF Conversion Growth Capex Maintenance Capex 1 Free Cash flow defined as Compliance EBITDA – Maintenance Capex (as defined in the prior Credit Agreement); Conversion defined as (FCF / Compliance EBITDA) 39 39 Source: Centuri financials

RIGGS HISTORICAL FINANCIAL PERFORMANCE Revenue Adjusted EBITDA and Margin ($ in millions) ($ in millions) >300 bps of margin expansion from 2019- $80 2020 due to improved performance across $458 both business segments, largely driven by $440 $401 Project Controls Group initiatives $58 $383 $55 $41 $41 13% 13% 11% 10% $0 $0 2018 2019 2020 LTM 3/31/21 2018 2019 2020 LTM 3/31/21 Adj. EBITDA EBITDA Margin 1,2 1 Capital Expenditures FCF and FCF Conversion ($ in millions) ($ in millions) $55 180% $54 $50 $53 $53 $52 $51 $48 $50 $50 160% $49 $48 $47 $47 $46 $45 $44 $44 140% $43 $42 $41 $29 $41 $40 $39 $27 $38 $38 $34 $26 $37 120% $36 $35 $35 $34 $30 $33 $8 $32 $32 $21 $31 100% $30 $7 $29 $29 $28 $27 $11 $26 $26 $25 80% $24 $23 $7 $23 $22 $21 $20 86% 86% $20 83% $19 $18 60% $17 $17 73% $16 $15 $14 $14 $21 $13 $20 $12 40% $11 $11 $10 $15 $14 $9 $8 $8 $7 20% $6 $5 $5 $4 $3 $2 $2 $1 $0 $0 0% 2018 2019 2020 LTM 3/31/21 2018 2019 2020 LTM 3/31/21 Growth Capex Maintenance Capex FCF FCF Conversion 1 Free Cash flow defined as Adjusted EBITDA – Maintenance Capex; Conversion defined as (FCF / Adjusted EBITDA) 2 40 Source: Riggs financials 40 Total Capex excludes nonrecurring Capex during 2018 and 2019; includes cash purchase of PP&E + non-cash purchase of PP&E under capital lease obligationsRIGGS HISTORICAL FINANCIAL PERFORMANCE Revenue Adjusted EBITDA and Margin ($ in millions) ($ in millions) >300 bps of margin expansion from 2019- $80 2020 due to improved performance across $458 both business segments, largely driven by $440 $401 Project Controls Group initiatives $58 $383 $55 $41 $41 13% 13% 11% 10% $0 $0 2018 2019 2020 LTM 3/31/21 2018 2019 2020 LTM 3/31/21 Adj. EBITDA EBITDA Margin 1,2 1 Capital Expenditures FCF and FCF Conversion ($ in millions) ($ in millions) $55 180% $54 $50 $53 $53 $52 $51 $48 $50 $50 160% $49 $48 $47 $47 $46 $45 $44 $44 140% $43 $42 $41 $29 $41 $40 $39 $27 $38 $38 $34 $26 $37 120% $36 $35 $35 $34 $30 $33 $8 $32 $32 $21 $31 100% $30 $7 $29 $29 $28 $27 $11 $26 $26 $25 80% $24 $23 $7 $23 $22 $21 $20 86% 86% $20 83% $19 $18 60% $17 $17 73% $16 $15 $14 $14 $21 $13 $20 $12 40% $11 $11 $10 $15 $14 $9 $8 $8 $7 20% $6 $5 $5 $4 $3 $2 $2 $1 $0 $0 0% 2018 2019 2020 LTM 3/31/21 2018 2019 2020 LTM 3/31/21 Growth Capex Maintenance Capex FCF FCF Conversion 1 Free Cash flow defined as Adjusted EBITDA – Maintenance Capex; Conversion defined as (FCF / Adjusted EBITDA) 2 40 Source: Riggs financials 40 Total Capex excludes nonrecurring Capex during 2018 and 2019; includes cash purchase of PP&E + non-cash purchase of PP&E under capital lease obligations

RECENT PERFORMANCE UPDATE Centuri Financial Summary Centuri Commentary ($ in Millions) Actual Performance » FY 2020 and Q1 2021 performance exceeded Centuri’s original budget across revenue, gross profit, and compliance EBITDA, largely attributable FYE YTD YTD LTM to weather events in the Southeast driving an increase in higher margin 2020 3/31/20 3/31/21 3/31/21 services, including emergency restoration services performed following tornados and ice storms in Texas Revenue $1,948 $333 $364 $1,979 » In addition to the impact of weather, revenue and compliance EBITDA % Y/Y Growth - - 9.1% - growth y/y reflects a higher volume of electric and gas infrastructure work Gross Profit $214 $7 $23 $230 under blanket and bid contracts % Margin 11.0% 2.0% 6.3% 11.6% » Gross profit and compliance EBITDA margins during the first quarter of the year reflect the typical business seasonality, which is lowest in Q1 Compliance EBITDA $219 $14 $28 $233 » LTM 3/31/21 includes $91 million of storm support revenue which % Margin 11.2% 4.2% 7.8% 11.8% typically generates a higher profit margin than core customer work, storm revenue varies from period to period given the unpredictable nature of Source: Centuri Financial Statements; Compliance Certificates weather-related events Riggs Financial Summary Riggs Commentary ($ in Millions) Actual Performance » The y/y increase in year-to-date performance is largely attributable to FYE YTD YTD LTM base business growth and price escalators, ramping of new utility MSAs, and accelerated growth across 5G Datacom 2020 3/31/20 3/31/21 3/31/21 » Gross profit and adjusted EBITDA margin expansion is driven by strong Revenue $440 $102 $120 $458 margin performance on overhead transmission projects and transition to % Y/Y Growth - - 17.5% - additional unit price contract structures in certain business units Gross Profit $66 $14 $18 $70 % Margin 15.0% 13.4% 14.9% 15.3% Adjusted EBITDA $55 $11 $14 $58 % Margin 12.6% 10.5% 11.5% 12.8% Source: Riggs Financial Statements 41 41 Source: Centuri and Riggs financialsRECENT PERFORMANCE UPDATE Centuri Financial Summary Centuri Commentary ($ in Millions) Actual Performance » FY 2020 and Q1 2021 performance exceeded Centuri’s original budget across revenue, gross profit, and compliance EBITDA, largely attributable FYE YTD YTD LTM to weather events in the Southeast driving an increase in higher margin 2020 3/31/20 3/31/21 3/31/21 services, including emergency restoration services performed following tornados and ice storms in Texas Revenue $1,948 $333 $364 $1,979 » In addition to the impact of weather, revenue and compliance EBITDA % Y/Y Growth - - 9.1% - growth y/y reflects a higher volume of electric and gas infrastructure work Gross Profit $214 $7 $23 $230 under blanket and bid contracts % Margin 11.0% 2.0% 6.3% 11.6% » Gross profit and compliance EBITDA margins during the first quarter of the year reflect the typical business seasonality, which is lowest in Q1 Compliance EBITDA $219 $14 $28 $233 » LTM 3/31/21 includes $91 million of storm support revenue which % Margin 11.2% 4.2% 7.8% 11.8% typically generates a higher profit margin than core customer work, storm revenue varies from period to period given the unpredictable nature of Source: Centuri Financial Statements; Compliance Certificates weather-related events Riggs Financial Summary Riggs Commentary ($ in Millions) Actual Performance » The y/y increase in year-to-date performance is largely attributable to FYE YTD YTD LTM base business growth and price escalators, ramping of new utility MSAs, and accelerated growth across 5G Datacom 2020 3/31/20 3/31/21 3/31/21 » Gross profit and adjusted EBITDA margin expansion is driven by strong Revenue $440 $102 $120 $458 margin performance on overhead transmission projects and transition to % Y/Y Growth - - 17.5% - additional unit price contract structures in certain business units Gross Profit $66 $14 $18 $70 % Margin 15.0% 13.4% 14.9% 15.3% Adjusted EBITDA $55 $11 $14 $58 % Margin 12.6% 10.5% 11.5% 12.8% Source: Riggs Financial Statements 41 41 Source: Centuri and Riggs financials

CENTURI HAS DEMONSTRATED STABLE, LONG-TERM PERFORMANCE Revenue ($ in millions) $1,979 $1,948 $1,751 $1,522 $1,246 $1,139 $1,009 $740 $651 $606 $483 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 LTM 3/31/21 Compliance EBITDA ($ in millions) $233 $219 $178 $141 $116 $111 $101 $97 $77 $65 $60 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 LTM 3/31/21 42 42 Source: Centuri Financials

CONSERVATIVE FINANCIAL POLICIES » Lower risk contract profile, focusing on recurring services MSA contracts with blue-chip utility operators; contract Operating pricing structures heavily weighted towards unit price and time & materials vs. lump-sum fixed price Philosophy » Target total leverage profile of <3.0x Leverage » Will increase leverage for key strategic M&A opportunities up to 4.0x » Goal of quickly delevering to <3.0x total leverage within ~2 years; strong ability and willingness to deleverage » Estimated liquidity at close of >$300 million Liquidity » Target liquidity of $200 million for ongoing business needs » Continued dividends to SWX based on 50% of trailing 3-year average of U.S. generated Net Income Capital Deployment » SWX commitment to cover the remaining 20% equity buyout of Linetec from 2022-2024 » Fully pre-payable capital structure to support deleveraging Capital Structure » Long-term funding at attractive rates while preserving operating, strategic and financial flexibility 43 43 Source: Centuri managementCONSERVATIVE FINANCIAL POLICIES » Lower risk contract profile, focusing on recurring services MSA contracts with blue-chip utility operators; contract Operating pricing structures heavily weighted towards unit price and time & materials vs. lump-sum fixed price Philosophy » Target total leverage profile of <3.0x Leverage » Will increase leverage for key strategic M&A opportunities up to 4.0x » Goal of quickly delevering to <3.0x total leverage within ~2 years; strong ability and willingness to deleverage » Estimated liquidity at close of >$300 million Liquidity » Target liquidity of $200 million for ongoing business needs » Continued dividends to SWX based on 50% of trailing 3-year average of U.S. generated Net Income Capital Deployment » SWX commitment to cover the remaining 20% equity buyout of Linetec from 2022-2024 » Fully pre-payable capital structure to support deleveraging Capital Structure » Long-term funding at attractive rates while preserving operating, strategic and financial flexibility 43 43 Source: Centuri management

APPENDIX 44 44APPENDIX 44 44

CENTURI COMPLIANCE EBITDA RECONCILIATION Centuri Compliance EBITDA Reconciliation ($ in millions) FY 2011 FY 2012 FY 2013 FY 2014 FY 2015 FY 2016 FY 2017 FY 2018 FY 2019 FY 2020 LTM 3/31/21 Centuri Standalone Audited Net Income $20.3 $16.0 $20.7 $24.3 $14.6 $20.5 $23.7 $26.9 $26.7 $53.6 $63.9 1 Goodwill Amortization, Net of Taxes and NCI - - - - 13.2 13.1 14.8 17.5 28.4 27.9 28.1 Centuri Net Income Segment of SWX $20.3 $16.0 $20.7 $24.3 $27.8 $33.6 $38.5 $44.4 $55.1 $81.5 $92.0 Income Tax Provision 13.7 10.3 12.6 14.8 18.5 19.9 2.4 18.4 21.4 31.1 34.5 Interest Expense 0.8 1.1 1 .1 3.8 7.8 6 .7 8.0 1 4.2 1 4.1 9 .3 8.0 Depreciation & Amortization Expense 25.2 37.4 43.0 48.9 56.7 55.7 49.0 57.4 87.6 96.7 98.5 Acquisition Related Transaction Costs - - - 5.1 - - 2.6 6.9 - - - Compliance EBITDA $60.0 $64.8 $77.4 $96.9 $110.8 $115.9 $100.5 $141.3 $178.2 $218.6 $233.0 Pro Forma Impact from Acquisitions - - - 11.1 - - 12.8 40.2 - - - Pro Forma Compliance EBITDA $60.0 $64.8 $77.4 $108.0 $110.8 $115.9 $113.3 $181.5 $178.2 $218.6 $233.0 1 Effective January 1, 2015, Centuri adopted the private company method of accounting for goodwill which requires amortization expense, which is reversed from the Southwest Gas Holdings consolidated financial statements 45 Source: Centuri financial information 45CENTURI COMPLIANCE EBITDA RECONCILIATION Centuri Compliance EBITDA Reconciliation ($ in millions) FY 2011 FY 2012 FY 2013 FY 2014 FY 2015 FY 2016 FY 2017 FY 2018 FY 2019 FY 2020 LTM 3/31/21 Centuri Standalone Audited Net Income $20.3 $16.0 $20.7 $24.3 $14.6 $20.5 $23.7 $26.9 $26.7 $53.6 $63.9 1 Goodwill Amortization, Net of Taxes and NCI - - - - 13.2 13.1 14.8 17.5 28.4 27.9 28.1 Centuri Net Income Segment of SWX $20.3 $16.0 $20.7 $24.3 $27.8 $33.6 $38.5 $44.4 $55.1 $81.5 $92.0 Income Tax Provision 13.7 10.3 12.6 14.8 18.5 19.9 2.4 18.4 21.4 31.1 34.5 Interest Expense 0.8 1.1 1 .1 3.8 7.8 6 .7 8.0 1 4.2 1 4.1 9 .3 8.0 Depreciation & Amortization Expense 25.2 37.4 43.0 48.9 56.7 55.7 49.0 57.4 87.6 96.7 98.5 Acquisition Related Transaction Costs - - - 5.1 - - 2.6 6.9 - - - Compliance EBITDA $60.0 $64.8 $77.4 $96.9 $110.8 $115.9 $100.5 $141.3 $178.2 $218.6 $233.0 Pro Forma Impact from Acquisitions - - - 11.1 - - 12.8 40.2 - - - Pro Forma Compliance EBITDA $60.0 $64.8 $77.4 $108.0 $110.8 $115.9 $113.3 $181.5 $178.2 $218.6 $233.0 1 Effective January 1, 2015, Centuri adopted the private company method of accounting for goodwill which requires amortization expense, which is reversed from the Southwest Gas Holdings consolidated financial statements 45 Source: Centuri financial information 45

RIGGS ADJUSTED EBITDA RECONCILIATION Riggs Distler Adjusted EBITDA Reconciliation ($ in millions) FY 2018 FY 2019 FY 2020 LTM 3/31/21 Net Income $10.2 ($0.4) $19.0 $22.0 Interest Expense 2.6 3.6 2.1 2.1 Income Taxes (6.8) 5.5 - 0.0 Depreciation & Amortization 18 .3 25 .4 28 .9 29.2 Reported EBITDA $24.3 $34.1 $50.0 $53.3 Management Adjustments 1 Management fees 5.0 2.5 - 0.0 Transaction costs and non-recurring professional fees 1.9 1.0 0.4 0.4 2 One-time project losses 3.5 3.3 - 0.0 Out-of-period contract adjustments - 1.2 0.6 0.5 One-time recruiting fees - 0.1 0.1 0.1 Non-recurring severance - - 0.1 0.2 Board of Director fees - 0.2 0.2 0.2 Stock based compensation - 0.9 1.3 1.1 3 COVID-19 non-operating expenses - - 0.7 0.6 Total Management Adjustments $10.4 $9.1 $3.4 $3.2 Management Adjusted EBITDA $34.7 $43.3 $53.4 $56.5 Diligence Adjustments 4 Reversal of out-of-period contract adjustments - (1.2) ( 0.6) (0.5) Stock based compensation (FY18) 0.6 - - 0.0 Non-operating (income)/expense 0.0 (0.0) (0.5) (0.1) Bank charges ( 0.4) (0.3) ( 0.2) (0.2) Rental fees 0.6 - - 0.0 Out-of-period normalization - (0.0) - (0.1) Total Diligence Adjustments $0.8 ($1.5) ($1.3) ($1.0) Diligence Adjusted EBITDA $35.5 $41.8 $52.1 $55.5 Pro Forma Adjustments 5 Pre-acquisition EBITDA 8.8 1.7 3.2 2.9 6 Run-rate cost infrastructure ( 3.8) ( 2.1) - - Total Pro Forma Adjustments $5.1 ($0.4) $3.2 $2.9 Pro Forma Adjusted EBITDA $40.5 $41.4 $55.4 $58.5 Utility Customer #1 MSA ramp 12.8 Utility Customer #2 MSA ramp 3.8 Total Run-Rate Adjustments - - - $16.6 Run-Rate Adjusted EBITDA $40.5 $41.4 $55.4 $75.1 1 Internal charges between Riggs and a former sister company for back-office support 2 Unrecoverable project write-offs including those inherited from acquisitions 3 Reconciliations exclude illustrative COVID add-backs related to operational disruptions ($1.286 million for LTM period); includes non-operating adjustments such as sanitation charges 4 Diligence uncovered that out-of period contracts were a part of normal course of business 5 Represents EBITDA from acquired businesses from FY18-20 where the businesses were not yet owned by Riggs (HT Sweeney, KT Power, Shelby Mechanical and New York Drilling) 6 FY18-19 burdens of newly hired management which were added back under management fees 46 46 Source: Riggs financial information; Riggs Quality of Earnings reportRIGGS ADJUSTED EBITDA RECONCILIATION Riggs Distler Adjusted EBITDA Reconciliation ($ in millions) FY 2018 FY 2019 FY 2020 LTM 3/31/21 Net Income $10.2 ($0.4) $19.0 $22.0 Interest Expense 2.6 3.6 2.1 2.1 Income Taxes (6.8) 5.5 - 0.0 Depreciation & Amortization 18 .3 25 .4 28 .9 29.2 Reported EBITDA $24.3 $34.1 $50.0 $53.3 Management Adjustments 1 Management fees 5.0 2.5 - 0.0 Transaction costs and non-recurring professional fees 1.9 1.0 0.4 0.4 2 One-time project losses 3.5 3.3 - 0.0 Out-of-period contract adjustments - 1.2 0.6 0.5 One-time recruiting fees - 0.1 0.1 0.1 Non-recurring severance - - 0.1 0.2 Board of Director fees - 0.2 0.2 0.2 Stock based compensation - 0.9 1.3 1.1 3 COVID-19 non-operating expenses - - 0.7 0.6 Total Management Adjustments $10.4 $9.1 $3.4 $3.2 Management Adjusted EBITDA $34.7 $43.3 $53.4 $56.5 Diligence Adjustments 4 Reversal of out-of-period contract adjustments - (1.2) ( 0.6) (0.5) Stock based compensation (FY18) 0.6 - - 0.0 Non-operating (income)/expense 0.0 (0.0) (0.5) (0.1) Bank charges ( 0.4) (0.3) ( 0.2) (0.2) Rental fees 0.6 - - 0.0 Out-of-period normalization - (0.0) - (0.1) Total Diligence Adjustments $0.8 ($1.5) ($1.3) ($1.0) Diligence Adjusted EBITDA $35.5 $41.8 $52.1 $55.5 Pro Forma Adjustments 5 Pre-acquisition EBITDA 8.8 1.7 3.2 2.9 6 Run-rate cost infrastructure ( 3.8) ( 2.1) - - Total Pro Forma Adjustments $5.1 ($0.4) $3.2 $2.9 Pro Forma Adjusted EBITDA $40.5 $41.4 $55.4 $58.5 Utility Customer #1 MSA ramp 12.8 Utility Customer #2 MSA ramp 3.8 Total Run-Rate Adjustments - - - $16.6 Run-Rate Adjusted EBITDA $40.5 $41.4 $55.4 $75.1 1 Internal charges between Riggs and a former sister company for back-office support 2 Unrecoverable project write-offs including those inherited from acquisitions 3 Reconciliations exclude illustrative COVID add-backs related to operational disruptions ($1.286 million for LTM period); includes non-operating adjustments such as sanitation charges 4 Diligence uncovered that out-of period contracts were a part of normal course of business 5 Represents EBITDA from acquired businesses from FY18-20 where the businesses were not yet owned by Riggs (HT Sweeney, KT Power, Shelby Mechanical and New York Drilling) 6 FY18-19 burdens of newly hired management which were added back under management fees 46 46 Source: Riggs financial information; Riggs Quality of Earnings report

PRO FORMA LEGAL STRUCTURE U.S. Borrower Centuri Group, Inc. Canadian Borrower Centuri Canada Centuri U.S. Division Inc. Division, Inc. Centuri Centuri Oil & Gas Group LLC Power Group LLC Union Non-Union Non-Union Non-Union Union Union Union Union Canyon New England NPL Linetec National Riggs W.S. Nicholls Pipeline Utility NPL Canada Construction Services, Powerline (Drum Construction Construction, Constructors, Ltd. 1 2 Co. LLC LLC Parent, Inc) Inc. Inc. Inc. 1 80% owned by Centuri as of June 2021; remaining 20% equity to be purchased by 2024 2 47 Owns a 50% equity interest in W.S. Nicholls Western Construction Ltd. 47 Source: Centuri managementPRO FORMA LEGAL STRUCTURE U.S. Borrower Centuri Group, Inc. Canadian Borrower Centuri Canada Centuri U.S. Division Inc. Division, Inc. Centuri Centuri Oil & Gas Group LLC Power Group LLC Union Non-Union Non-Union Non-Union Union Union Union Union Canyon New England NPL Linetec National Riggs W.S. Nicholls Pipeline Utility NPL Canada Construction Services, Powerline (Drum Construction Construction, Constructors, Ltd. 1 2 Co. LLC LLC Parent, Inc) Inc. Inc. Inc. 1 80% owned by Centuri as of June 2021; remaining 20% equity to be purchased by 2024 2 47 Owns a 50% equity interest in W.S. Nicholls Western Construction Ltd. 47 Source: Centuri management

THANK YOU 48 CONFIDENTIALTHANK YOU 48 CONFIDENTIAL