ufc_3_550_01_2016_c3.pdf

UFC 3-550-01

1 September, 2016

Change 3, 01 November 2019

UNIFIED FACILITIES CRITERIA (UFC)

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

EXTERIOR ELECTRICAL POWER

DISTRIBUTION

EXTERIOR ELECTRICAL POWER DISTRIBUTION

Any copyrighted material included in this UFC is identified at its point of use.

Use of the copyrighted material apart from this UFC must have the permission of the copyright holder.

U.S. ARMY CORPS OF ENGINEERS

NAVAL FACILITIES ENGINEERING COMMAND (Preparing Activity)

AIR FORCE CIVIL ENGINEER CENTER

Record of Changes (changes are indicated by \1\ ... /1/)

Change No. Date Location 1 23 Mar 2017 Removed reference to IEEE C57.12.22 and updated reference to IEEE C57.12.34 in section 3-5.1 and Appendix A references.

2 13 Mar 2019 Section 1-3 and Appendix A revised for cybersecurity requirements. Section 1-4 Cybersecurity added.

Added the clarification Notes to section 2-2, 3-4, 3-5.1, 3-6.1, and Appendix A.

Section 3-5 Pad-mounted transformer revised Section 3-10.9 Sectionalizer added.

Section 3-10.10. Ground Connections revised.

Section 3.11.6 Locating Underground Structures revised.

Revised section 3-14.2.1.

Appendix A added references to IEEE Guides mitigating bird and wildlife-related power interruptions.

3 01 Nov 2019 Added Environmental Severity Classification and humidity design requirements and updated corrosion prevention requirements in 1-3.1, Appendix A and Appendix D.

FOREWORD

The Unified Facilities Criteria (UFC) system is prescribed by MIL-STD 3007 and provides planning, design, construction, sustainment, restoration, and modernization criteria, and applies to the Military Departments, the Defense Agencies, and the DoD Field Activities in accordance with USD (AT&L) Memorandum dated 29 May 2002. UFC will be used for all DoD projects and work for other customers where appropriate. All construction outside of the United States is also governed by Status of Forces Agreements (SOFA), Host Nation Funded Construction Agreements (HNFA), and in some instances, Bilateral Infrastructure Agreements (BIA.)

Therefore, the acquisition team must ensure compliance with the most stringent of the UFC, the SOFA, the HNFA, and the BIA, as applicable.

UFC are living documents and will be periodically reviewed, updated, and made available to users as part of the Services’ responsibility for providing technical criteria for military construction. Headquarters, U.S. Army Corps of Engineers (HQUSACE), Naval Facilities Engineering Command (NAVFAC), and Air Force Civil Engineer Center (AFCEC) are responsible for administration of the UFC system. Defense agencies should contact the preparing service for document interpretation and improvements. Technical content of UFC is the responsibility of the cognizant DoD working group. Recommended changes with supporting rationale should be sent to the respective service proponent office by the following electronic form: Criteria Change Request. The form is also accessible from the Internet sites listed below.

UFC are effective upon issuance and are distributed only in electronic media from the following source:

• Whole Building Design Guide web site http://dod.wbdg.org/.

Refer to UFC 1-200-01, General Building Requirements, for implementation of new issuances on projects.

AUTHORIZED BY:

JAMES C. DALTON, P.E. JOSEPH E. GOTT, P.E.

Chief, Engineering and Construction Chief Engineer U.S. Army Corps of Engineers Naval Facilities Engineering Command

EDWIN H. OSHIBA, SES, DAF MICHAEL McANDREW Deputy Director of Civil Engineers DASD (Facilities Investment and Management) DCS/Logistics, Engineering & Force Protection Office of the Assistant Secretary of Defense

(Energy, Installations and Environment)

REVISION SUMMARY SHEET

Document: 3-550-01, Exterior Electrical Power Distribution

Superseding: UFC 3-550-01, Exterior Electrical Power Distribution, dated Feb 3, 2010, including Change 1, dated Jul 1, 2012.

Description: This UFC 3-550-01 provides design guidance for the design of exterior distribution systems.

Reasons for Document:

• Provide technical requirements.

• Incorporate new and revised industry standards.

Impact: There are negligible cost impacts associated with this UFC. However, the following benefits should be realized.

• Standardized guidance has been prepared to assist engineers with unique installation requirements.

• Exterior electrical equipment design criteria are specified to ensure that a reliable installation is realized.

Unification Issues:

The Air Force has the following noted exceptions:

• Paragraph 3-11.5.1 Permits use of pad-mounted sectionalizing cabinets instead of manholes.

• Paragraph 3-11.5.2 Prohibits T splices and Y splices on any MV system.

• Paragraph 3-11.5.5 Does not permit manholes in aircraft aprons.

The Navy has the following noted exceptions:

• Paragraph 3-2.3 Requires 600V insulated neutral conductor in pole riser and ductbanks.

• Paragraph 3-7 Requires switchgear to be SF-6 gas or high fire point liquid insulated.

• Paragraph 3-11.8 Does not permit concentric neutral conductors in ductbanks.

• Paragraph 3-11.8 Requires EPR insulation for MV cables.

Change 3, 01 November 2019 i

TABLE OF CONTENTS

CHAPTER 1 GENERAL

1-1 PURPOSE

1-2 APPLICABILITY

1-2.1 NFPA 70 and IEEE C2

1-2.2 Additional References

1-2.3 Exclusions

1-3 GENERAL BUILDING REQUIREMENTS

1-3.1 \3\ Environmental Severity and Humid Locations...………………………2

1-4 CYBERSECURITY

1-5 CRITERIA WAIVER PROCESS

1-6 REFERENCES

1-7 UTILITY-OWNED AND OPERATED DISTRIBUTION SYSTEMS ON

FEDERAL PROPERTY

CHAPTER 2 ELECTRICAL POWER REQUIREMENTS

2-1 ELECTRICAL POWER REQUIREMENTS: GENERAL

2-2 SELECTION OF PRIMARY VOLTAGE

2-3 DESIGN FOR MAINTENANCE

CHAPTER 3 DESIGN CRITERIA

3-1 MAIN AND UTILIZATION ELECTRIC SUPPLY STATIONS

3-1.1 Main Electric Supply Stations

3-1.2 Utilization Electric Supply Stations

3-2 GENERAL ELECTRICAL REQUIREMENTS

3-2.1 Industry Standards

3-2.2 Arc Flash Analysis Criteria

3-2.3 System Design

3-2.4 Pad-Mounted Equipment

3-3 PRIMARY UNIT SUBSTATIONS

3-4 SECONDARY UNIT SUBSTATIONS

3-5 PAD-MOUNTED DISTRIBUTION TRANSFORMERS

3-5.1 Reference Criteria

3-5.2 Configuration

3-5.3 Size and Secondary Voltage

Change 3, 01 November 2019 ii

3-5.4 Winding Configuration

3-5.5 Surge Protection

3-5.6 Drawing Details

3-6 MEDIUM VOLTAGE SWITCHGEAR

3-6.1 Metal-Clad Switchgear

3-6.2 Metal-Enclosed Switchgear

3-6.3 Circuit Breaker Operation Design

3-7 PAD-MOUNTED SWITCHGEAR (SWITCHES)

3-8 PAD-MOUNTED SECTIONALIZING TERMINATION CABINETS

3-9 CAPACITORS

3-9.1 Application

3-9.2 Disconnect Design

3-10 OVERHEAD POWER DISTRIBUTION

3-10.1 Drawing Details

3-10.2 Pole Types

3-10.3 Conductors

3-10.4 Pole-Mounted Transformers

3-10.5 Pole-Top Switches

3-10.6 Surge Arresters

3-10.7 Fuse Protection

3-10.8 Automatic Circuit Reclosing

3-10.9 Sectionalizer 3-10.10 Ground Connections

3-11 UNDERGROUND ELECTRICAL SYSTEMS

3-11.1 Underground Distribution General Criteria

3-11.2 Ductbanks

3-11.3 Direct Buried Wiring Methods

3-11.4 Directional Boring

3-11.5 Underground Structures (Manholes and Handholes)

3-11.6 Locating Underground Structures

3-11.7 Pull Boxes

3-11.8 Medium Voltage Cable

3-12 CONCRETE FOR UNDERGROUND ELECTRICAL SYSTEMS

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3-13 HOUSING DISTRIBUTION

3-14 DISTRIBUTION SYSTEM GROUNDING

3-14.1 Separation of Grounding Conductors

3-14.2 Materials and Special Requirements

3-14.3 Low Voltage Grounding Interface With Utilization Electric Supply Stations

3-14.4 Grounding Requirements – Fences

3-15 METERING

3-16 EXTERIOR SITE LIGHTING

3-17 CATHODIC PROTECTION SYSTEMS

3-18 ENVIRONMENTAL CONSIDERATIONS

3-19 FIRE PROTECTION CONSIDERATIONS

APPENDIX A REFERENCES

APPENDIX B DIRECTIONAL BORING

B-1 CONDUIT TYPE

B-1.1 Conduit Design – 1,000 Volts to 34,500 Volts

B-1.2 Conduit Design – Less Than 1,000 Volts

B-1.3 Conduit Design – Branch Circuit Wiring Less Than 600 Volts

B-2 INSTALLATION METHODS

B-2.1 Ampacity

B-2.2 Installation

B-2.3 Allowable Pulling Tension

B-2.4 Termination into Equipment Pads

B-2.5 Multiple Conduits and Wiring Methods

B-2.6 Joining Methods

B-2.7 Transition from HDPE to PVC

B-3 DOCUMENTATION

APPENDIX C BEST PRACTICES – GENERAL ELECTRICAL POWER

REQUIREMENTS

C-1 EXTERIOR SYSTEM DESIGN

C-2 METERING

C-3 DEMARCATION

C-4 SUBSTATIONS AND SWITCHING STATIONS

Change 3, 01 November 2019 iv

APPENDIX D GLOSSARY

D-1 ACRONYMS

D-2 DEFINITION OF TERMS

FIGURES

Figure B-1 HDPE or Rigid Conduit Electrical Equipment Transition

Figure B-2 Pavement Covered Area to Electrical Equipment Transition – Rigid Conduit (45˚–90˚)

Figure B-3 Pavement Covered Area to Electrical Equipment Transition – HDPE Conduit (20˚–45˚)

Figure B-4 Non-Pavement Covered Area to Electrical Equipment Transition – Rigid Conduit (45˚–90˚)

Figure B-5 Non-Pavement Covered Area to Electrical Equipment Transition – HDPE Conduit (20˚–45˚)

Figure B-6 HDPE-to-PVC Pavement Covered Area Concrete Ductbank Transition

Figure B-7 HDPE-to-PVC Non-Pavement Covered Area Concrete Ductbank Transition

Figure B-8 HDPE-to-Manhole Pavement Covered Area Transition

Figure B-9 HDPE-to-Manhole Pavement Covered Area Transition

Change 3, 01 November 2019

CHAPTER 1 GENERAL

1-1 PURPOSE.

This UFC provides policy and guidance for design criteria and standards for electrical power and distribution systems. The information provided here must be utilized by electrical engineers in the development of the plans, specifications, calculations, and Design/Build Request for Proposals (RFP) and must serve as the minimum electrical design requirements. It is applicable to the traditional electrical services customary for Design-Bid-Build construction contracts and for Design-Build construction contracts.

Project conditions may dictate the need for a design that exceeds these minimum requirements.

UFC 3-501-01 provides the governing criteria for electrical systems, explains the delineation between the different electrical-related UFCs, and refers to UFC 3-550-01 for exterior electrical system requirements. Refer to UFC 3-501-01 for design analysis, calculation, and drawing requirements.

1-2 APPLICABILITY.

The design criteria and standards contained within are the minimum requirements acceptable for military installations for efficiency, economy, durability, maintainability, and reliability of electrical power supply and distribution systems. The criteria and standards herein are not intended to be retroactively mandatory.

1-2.1 NFPA 70 and IEEE C2.

Comply with the requirements of NFPA 70 and IEEE C2. Generally, IEEE C2 is the basis for UFC 3-550-01 and NFPA 70 is the basis for UFC 3-520-01. However, there are exceptions to which standard applies to each UFC, including:

• Systems covered by other UFCs, such as airfield lighting and shore power systems.

• Exterior circuits such as lighting and service entrance (overhead and underground), which are covered by NFPA 70.

For medium voltage applications, feeder conductor sizing is permitted to be determined by qualified persons under engineering supervision as defined by NFPA 70 Article 215.2

(B) (3), Supervised Installations.

1-2.2 Additional References.

Comply with UFC 3-560-01 for electrical safety requirements applicable to the installation and operation of electrical systems.

Comply with UFC 4-010-01 and UFC 4-020-01 for security requirements related to exterior electrical distribution systems.

Change 3, 01 November 2019

1-2.3 Exclusions.

Onsite generation is not addressed by this UFC.

1-3 GENERAL BUILDING REQUIREMENTS.

\2\ Comply with UFC 1-200-01, DoD Building Code (General Building Requirements).

UFC 1-200-01 provides applicability of model building codes and government unique criteria for typical design disciplines and building systems, as well as for accessibility, antiterrorism, physical security, cybersecurity, high performance and sustainability requirements, and safety. Use this UFC in addition to UFC 1-200-01 and the UFC and government criteria referenced therein.

1-3.1 \3\ Environmental Severity and Humid Locations.

In corrosive and humid environments, provide design detailing, and use materials, systems, components, and coatings that are durable and minimize the need for preventative and corrective maintenance over the expected service life of the component or system. UFC 1-200-01, section titled “Corrosion Prone Locations” identifies corrosive environments and humid locations requiring special attention. UFC 1-200-01, section titled “Requirements for Corrosion Prone Locations” provides examples of necessary actions. To determine Environmental Severity Classifications (ESC) for specific project locations refer to UFC 1-200-01 Appendix titled “Environmental Severity Classifications (ESC) for DoD Locations”. /3/

1-4 CYBERSECURITY.

All facility-related control systems (including systems separate from a utility monitoring and control system) must be planned, designed, acquired, executed, and maintained in accordance with UFC 4-010-06 and as required by individual Service Implementation Policy.

Cybersecurity is implemented to mitigate vulnerabilities to all DoD real property facility-related control systems to a level that is acceptable to the System Owner and Authorizing Official. UFC 4-010-06 provides requirements for integrating cybersecurity into the design and construction of control systems. /2/

1-5 CRITERIA WAIVER PROCESS.

The criteria waiver process is provided in MIL-STD 3007.

1-6 REFERENCES.

Codes and standards are referenced throughout this UFC. The publication date of the code or standard is not routinely included with the document identification throughout the text of the document. In general, the latest issuance of a code or standard has been assumed for use. Refer to Appendix A to determine the publication date of the codes and standards referenced in this UFC.

1-7 UTILITY-OWNED AND OPERATED DISTRIBUTION SYSTEMS ON

FEDERAL PROPERTY.

This UFC does not apply to:

• Utility-owned and operated distribution systems with right-of-way or easements on Federal property.

• Military installations that have privatized their electrical distribution system.

Change 3, 01 November 2019

CHAPTER 2 ELECTRICAL POWER REQUIREMENTS

2-1 ELECTRICAL POWER REQUIREMENTS: GENERAL.

Virtually all military bases have an existing overhead and underground distribution system that has been in service for many years. As part of any new design project, review the existing design with base personnel to determine which existing features should not be duplicated in future designs. Address design preferences with responsible engineering and operations personnel as part of the system design analysis.

2-2 SELECTION OF PRIMARY VOLTAGE.

NEMA C84.1 establishes typical voltages and voltage ranges for 60 Hz systems.

Facilities located outside of the United States must also comply with the applicable host nation standards; refer to UFC 1-202-01 and UFC 3-510-01 Foreign Voltage and Frequencies Guide (inactive), for additional information.

2-3 DESIGN FOR MAINTENANCE.

Design primary distribution system equipment installations with future periodic maintenance as a principal consideration. Equipment must be capable of removal from service while minimizing the outage time of affected facilities and missions. Looped and alternate feed designs are essential to allow periodic maintenance.

Provide maintenance criteria with the design analysis as part of the basis for the design as specified in UFC 3-501-01.

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CHAPTER 3 DESIGN CRITERIA

3-1 MAIN AND UTILIZATION ELECTRIC SUPPLY STATIONS.

For all main and electric supply stations/substations, comply with the requirements of IEEE C2 Part 1, Rules for the Installation and Maintenance of Electric Supply Stations and Equipment, as follows:

• Electric Supply Stations are defined as stations that transform the energy level (voltage) for further bulk distribution at medium voltage levels.

• Comply with the requirements of NFPA 70 for the low voltage equipment in a main or electric supply station (equipment that is being served from a Utilization Electric Supply Station).

3-1.1 Main Electric Supply Stations.

The main electric supply station is the installation/utility interface point where further transmission, distribution and utilization of electrical power, the monitoring and control of such power or equipment and the protection of electrical equipment or systems usually becomes the sole responsibility of the Government or their contracted representatives.

Coordinate the design of new stations, or modifications to existing stations with the supplying utility and with any other suppliers or users of power supplied through the station.

3-1.2 Utilization Electric Supply Stations.

Utilization Electric Supply Stations are defined as equipment such as pole or pad-mounted transformers, secondary unit substations, or primary unit substations that transforms the energy level (voltage) to a utilization voltage for consumer use. Some examples of Utilization Electric Supply Stations are station service transformers (serving low voltage equipment in a Main Electric Supply Station), a lighting transformer (serving equipment for a roadway lighting system), a pole or pad-mounted transformer (serving a building), or a secondary unit substation (serving piers and wharfs electrical systems)

3-2 GENERAL ELECTRICAL REQUIREMENTS.

Refer to Appendix C for Best Practices-General Electrical Power Requirements.

3-2.1 Industry Standards.

Overhead systems – comply with the requirements of IEEE C2 Part 2, Safety Rules for the Installation and Maintenance of Overhead Electric Supply and Communication Lines.

Underground systems – comply with the requirements of IEEE C2 Part 3, Safety Rules for the Installation and Maintenance of Underground Electric Supply and Communication Lines.

Change 3, 01 November 2019

3-2.2 Arc Flash Analysis Criteria.

Refer to UFC 3-560-01 Section 1-4.1.1 for arc-flash criteria and the delineation points between IEEE C2 and NFPA 70E conformance requirements.

3-2.3 System Design.

Design new primary distribution systems as four wire, multi-grounded systems that are wye connected at the source transformer. Provide a system grounded neutral conductor throughout the system. Provide a bare conductor for the neutral on overhead systems.

Note: For the Navy, provide a neutral that is a 600 volt insulated conductor for pole riser and underground systems.

When a project is limited to connecting to an existing three wire system and the primary electrical characteristics are established and defined, continuation of the existing system is permitted with the following requirements:

• For extensions from underground structures, provide a four wire extension. Bond the grounded neutral conductor at each end of the extension to the applicable grounding electrode systems.

• For extensions from overhead pole lines, provide a four wire extension.

Bond the grounded neutral conductor at each end of the extension to the applicable grounding electrode systems.

Note: Design of the extensions as four wire systems does not change any circuit classifications. It provides an extended grounding electrode system to facilitate any future circuit conversions to four wire systems.

3-2.4 Pad-Mounted Equipment.

Provide pad-mounted equipment foundation pads and ensure a minimum of 10 ft (3 m) clear workspace in front of pad-mounted equipment for hot stick work. Orient equipment so that adjacent equipment will not interfere with the clear workspace.

Provide bollards in areas where equipment is subject to vehicular damage.

3-3 PRIMARY UNIT SUBSTATIONS.

Provide primary unit substations to distribute underground medium voltage circuits.

Comply with the following industry standards as applicable for the specified configuration:

• IEEE C37.06, AC High-Voltage Circuit Breakers Rated on a Symmetrical Basis – Preferred Ratings and Related Required Capabilities.

• IEEE C37.46, High Voltage Expulsion and Current-Limiting Type Power Class Fuses and Fuse Disconnection Switches.

Change 3, 01 November 2019

• IEEE C37.121, Switchgear – Unit Substations Requirements.

• IEEE C57.12.28, Pad-Mounted Equipment – Enclosure Integrity.

• IEEE C57.12.00, General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers.

• IEEE C57.12.80, Terminology for Power and Distribution Transformers.

• IEEE C57.12.90, Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers.

• IEEE C57.96, Loading Dry-Type Distribution and Power Transformers.

• IEEE C57.98, Guide for Transformer Impulse Tests.

• IEEE C37.74, IEEE Standard Requirements for Subsurface, Vault, and Padmounted Load- Interrupter Switchgear and Fused Load-Interrupter Switchgear for Alternating Current Systems up to 38 kV.

3-4 SECONDARY UNIT SUBSTATIONS.

Provide secondary unit substations when secondary currents exceed 3,000 amperes at 1,000 volts and below. Comply with the following industry standards as applicable for the specified configuration:

• IEEE C57.12.28, Pad-Mounted Equipment – Enclosure Integrity.

• IEEE 57.12.50, Ventilated Dry-Type Distribution Transformers, 1 to 500 kVA, Single-Phase, and 15 to 500 kVA Three-Phase, with High-Voltage 601 to 34,500 Volts, Low-Voltage 120-600 Volts.

• IEEE 57.12.51, Ventilated Dry-Type Power Transformers, 501 kVA and larger, Three-Phase, with High-Voltage 601 to 34,500 Volts, Low-Voltage 208Y/120 to 4160 Volts.

• IEEE C57.12.00, General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers.

• IEEE C57.12.01, General Requirements for Dry-Type Distribution and Power Transformers Including Those with Solid-Cast and/or Resin- Encapsulated Windings.

• IEEE C57.12.80, Terminology for Power and Distribution Transformers.

• IEEE C57.12.90, Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers.

• IEEE C57.12.91, Test Code for Dry-Type Distribution and Power Transformers.

• IEEE C57.96, Loading Dry-Type Distribution and Power Transformers.

• IEEE C57.98, Guide for Transformer Impulse Tests.

Change 3, 01 November 2019

• IEEE C57.124, Detection of Partial Discharge and the Measurement of Apparent Charge in Dry-Type Transformers.

3-5 PAD-MOUNTED DISTRIBUTION TRANSFORMERS.

3-5.1 Reference Criteria.

Comply with the following industry standards:

• IEEE C57.12.28, Pad-Mounted Equipment – Enclosure Integrity.

• IEEE C57.12.00, General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers.

• \1\IEEE C57.12.34, Pad-Mounted, Compartmental-Type, Self-Cooled, Three-Phase Distribution Transformers, 10 MVA and Smaller High- Voltage, 34.5 kV Nominal System Voltage and Below; Low-Voltage, 15 kV Nominal System Voltage and Below. /1/

• IEEE C57.12.80, Terminology for Power and Distribution Transformers.

• IEEE C57.12.90, Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers.

• IEEE C57.98, Guide for Transformer Impulse Tests.

3-5.2 Configuration.

Use dead-front construction for pad-mounted transformers unless not available within system parameters.

Three-phase pad-mounted transformers must be loop-feed capable with 6 bushings.

Provide two-position, oil-immersed, load break switches that are appropriate for the application. If the transformer might be used as part of a loop-feed design, provide three switches to permit closed transition loop feed and sectionalizing. If the transformer will be installed at the end of a radial supply with no intention of future loop feed capability, provide a single on-off switch. Provide a spare conduit in the high voltage section extending 5 ft (1.5 m) out from the transformer pad.

3-5.3 Size and Secondary Voltage.

Do not use pad-mounted transformers with secondary currents exceeding 3,000 amperes because of the size and quantity of secondary conductors. Transformers rated above 1,000 kVA serving 208Y/120 volt loads and above 2,500 kVA serving 480Y/277 volt loads must be in a secondary unit substation configuration.

Minimize double transformations to reduce energy consumption and to minimize items of equipment. Provide two \2\liquid/2/-filled pad-mounted transformers in lieu of one 480Y/277 volt service if the required 208Y/120 volt load using dry-type transformers exceeds 40 percent of the 480 volt service transformer capability. Connect equipment

Change 3, 01 November 2019 at the highest available voltage to minimize the capital cost and energy losses of transformation equipment.

3-5.4 Winding Configuration.

Provide \2\step-down/2/ delta-wye \2\grounded connections and step-up grounded wye-wye/2/ connections for three phase systems.

3-5.5 Surge Protection.

Provide bushing-mounted elbow type arresters at the ends of all radials and in normally open locations in loops. Provide arresters for all voltage levels above 5 kV.

3-5.6 Drawing Details.

When using a pad-mounted transformer, select the applicable pad-mounted transformer detail in AutoCAD or PDF format from:

http://www.wbdg.org/ccb/NAVGRAPH/graphtoc.pdf , supply the missing data, and incorporate that detail onto the contract drawings. Pad-mounted transformer details are contained in the UFGS 26 27 14.00 20 Electricity Metering file. These drawing details represent typical situations but may not meet all requirements. Modify transformer details as required to indicate the actual requirements for each particular installation.

In rare cases when “live front construction” is required due to equipment ratings (available system fault current values), obtain approval from the Authority Having Jurisdiction (AHJ), as defined in UFC 1-200-01. Do not use the pad-mounted transformer details to show secondary unit substations.

3-6 MEDIUM VOLTAGE SWITCHGEAR.

3-6.1 Metal-Clad Switchgear.

Metal-clad switchgear can include either SF6 or vacuum style breakers and must consist of a single section or multiple section line-up of NEMA 1 or NEMA 3R enclosures. Either walk-in or non-walk-in construction can be provided. Medium voltage metal-clad switchgear can be provided as unit substation construction or as stand-alone switchgear. The sections must contain the breakers and the necessary accessory components. The equipment must be factory-assembled (except for necessary shipping splits) and be operationally checked before shipment. As an electrical safety consideration, provide a remote racking mechanism to rack breakers in and out. As an electrical safety consideration, provide ground ball studs on the load side of each circuit breaker to allow for connection of temporary grounding sets.

Comply with the following industry standards:

• IEEE C37.06, AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis – Preferred Ratings and Related Required Capabilities.

• IEEE C37.121, Switchgear – Unit Substations Requirements.

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• IEEE C37.04, Rating Structure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis.

• IEEE C37.20.2, Metal-Clad Switchgear.

• IEEE C37.90, Relays and Relay Systems Associated with Electric Power Apparatus.

3-6.2 Metal-Enclosed Switchgear.

Do not use metal-enclosed switchgear. Instead, use either a vacuum fault interrupter (VFI) in a unit substation configuration or pad-mounted switchgear.

3-6.3 Circuit Breaker Operation Design.

Provide batteries with battery charger for dc opening and closing of circuit breakers. Do not use ac or capacitor control methods.

3-7 PAD-MOUNTED SWITCHGEAR (SWITCHES).

For the Navy, utilize multi-way pad-mounted switchgear when switching, isolation, or electrical protection is required. Specify SF6 gas or high fire point liquid (non-temperature dependent) insulation technology and vacuum bottle interruption technology. Specify dead front construction with stainless steel tanks and operator full size viewing windows for each switching way. Specify three position (On/Off/Ground) switch ways for all new construction. For switch replacements when existing switching arrangement is On/Off/Tie, a similar arrangement without ground position is permissible.

Specify switch design which incorporates operating handles on the opposite side of the tank from the cable entrance bushings, terminations and cables. Specify 600 ampere dead break connectors with 200 ampere interface bushings for each switch way.

Coordinate with the Activity and include ground fault circuit indicators in accordance with the base design standard. Air-insulated (fused or non-fused) technology is not permitted. Comply with the following industry standards:

• IEEE C57.12.28, Pad-Mounted Equipment – Enclosure Integrity.

• IEEE C37.60, Requirements for Overhead, Pad-Mounted, Dry Vault, and Submersible Automatic Circuit Reclosers and Fault Interrupters for Alternating Current Systems Up to 38 kV.

• IEEE C37.74, IEEE Standard Requirements for Subsurface, Vault, and Padmounted Load- Interrupter Switchgear and Fused Load-Interrupter Switchgear for Alternating Current Systems up to 38 kV.

For the Army and Air Force, air-insulated and fused switches can be used in either a live-front or dead-front configuration. Do not use air-insulated switches in corrosive and high humidity areas as defined in UFC 3-501-01 unless the installation experience for the installed location confirms that switch corrosion and tracking is not a problem.

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3-8 PAD-MOUNTED SECTIONALIZING TERMINATION CABINETS.

Apply pad-mounted sectionalizing termination cabinets only when switching, isolation, or electrical protection for the downstream circuit is not required or anticipated.

Sectionalizing termination cabinets can be used instead of in-line splices in manholes or for minor loads that do not warrant the expense of pad-mounted switchgear.

Sectionalizing cabinets are available up to 35 kV. Provide low profile sectionalizing termination cabinets when the conductor size is 4/0 AWG or smaller. Coordinate with the Activity and include ground fault circuit indicators in accordance with the base design standard.

3-9 CAPACITORS.

3-9.1 Application.

Do not use capacitors unless they are needed for power factor correction or to minimize line losses. Verify the need by a system analysis; the analysis must consider the potential adverse effects of transients caused by capacitor switching. Refer to TSEWG TP-2: Capacitors for Power Factor Correction, at http://www.wbdg.org/ccb/browse_cat.php?o=29&c=248 for additional information if power factor correction is considered.

Underground distribution has more capacitance than equivalent overhead distribution.

When converting from overhead distribution to underground distribution, provide pad-mounted capacitors on a distribution system only if supported by the design analysis.

Do not automatically replace existing pole-mounted capacitors with equivalent pad-mounted capacitors.

3-9.2 Disconnect Design.

For safety purposes, include an oil switch disconnect with pole-mounted capacitors.

3-10 OVERHEAD POWER DISTRIBUTION.

Design overhead lines to IEEE C2 Grade B construction complying with the following:

a. Limit the initial loaded conductor tension to a maximum of 50% of the conductor rated breaking strength. Lesser tensions are usually applicable and generally more preferred. Utility distribution line design is generally in the range of 25% to 35% of the rated breaking strength.

b. Provide clearance requirements using final sag values in conformance with IEEE C2 Part 2.

c. Limit the maximum design tensions for any conductors to 4,750 pounds (2,154 kg). Base all clearance values on the following maximum conductor temperatures.

• Copper phase conductors – 167 degrees F (75 degrees C).

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• Aluminum/aluminum alloy phase conductors – 194 degrees F (90 degrees C).

• Neutral conductors for multi-phase circuits – 120 degrees F (49 degrees C).

• The maximum conductor temperature for single-phase neutral conductors is identical to the phase conductors.

Match the existing base construction methods. Match those construction methods used by the local utility when directed. Where new overhead distribution is required, route the overhead distribution along roadways and other major topographical features; the poles must be accessible for future maintenance or work. Coordinate pole locations with land-use planning to ensure that new poles do not interfere with future facility plans.

3-10.1 Drawing Details.

Use NAVFAC pole details OH-1.1 through OH-41. NAVFAC pole details are available in Adobe PDF format and in AutoCAD format http://www.wbdg.org/ccb/NAVGRAPH/graphtoc.pdf. In situations where an applicable pole detail has not been developed, provide new detail drawings as required. For designer developed details, provide a level of detail equivalent to NAVFAC pole details and include material requirements. Refer to UFC 3-501-01 for additional pole detail requirements.

3-10.2 Pole Types.

Use solid wood poles for electric distribution lines. Concrete or steel poles may be justified for medium-voltage distribution circuits where wood poles do not provide adequate strength, or where climatic conditions cause wood poles to deteriorate rapidly.

Do not use laminated wood poles for electric distribution lines.

3-10.3 Conductors.

Due to the increasing technology improvements with aluminum conductors and connectors, and the economic disadvantage of providing copper conductors, provide aluminum conductor steel reinforced (ACSR) or aluminum alloys for new overhead lines and extensions of existing lines. Do not use ACSR conductors in corrosive and high humidity areas. For corrosive and high humidity areas, provide Type ACSS conductors.

Except for grounding systems, the use of copper conductors is prohibited without specific approval and documentation by the applicable local engineering authority. The local engineering authority is defined by the following:

• For the Navy, the Facilities Engineering Command (FEC) organization’s chief engineer has the authority to use copper product for their applicable jurisdiction.

Change 3, 01 November 2019

• For the Army, the Installation Department of Public Works Chief Engineer has the authority to use copper product for their applicable jurisdiction if documented in the planning process and the design analysis.

• For the Air Force, the Base Civil Engineer has the authority to exercise the criteria option of copper product for their applicable jurisdiction if documented in the planning process and the design analysis.

3-10.4 Pole-Mounted Transformers.

3-10.4.1 Maximum kVA Rating.

Provide pad-mounted transformers rather than pole-mounted transformers for new three-phase installations larger than 75 kVA.

Limit pole-mounted transformer sizes (except for projects involving system conversions to a different operating voltage) as follows:

• Three-phase installations – limited to three 25 kVA transformers or smaller.

• Single-phase installations – limited to one 75 kVA transformer or smaller.

3-10.4.2 Configuration.

Use only single phase transformers for pole-mounted installations. For single phase installations and when banking single phase transformers for three phase applications, apply phase-to-neutral primary connections unless installed on three wire distribution systems.

Do not use self-protected transformers. Self-protected transformers have internal primary fuses that must be replaced by experienced personnel.

3-10.4.3 Mounting and Location.

Do not use pole-platform mounting (two-pole structure or H-frame).

Aerially mounted installations might supply several buildings. When that is the case, install the transformers at the pole location closest to the building with the greatest load.

Secondary wiring should drop directly to the buildings served, if the span does not exceed 125 feet; otherwise, intermediate poles are required.

3-10.5 Pole-Top Switches.

Pole top switches are installed at important system locations to allow either isolation of the downstream circuit or cross-connection to a different circuit. Where ground operated, gang type, three phase, air break switches are used with non-insulated operator handles, provide a metal plate or grate at ground level for the operator to stand on when operating the switch. Connect the metal plate or grate to the pole ground

Change 3, 01 November 2019 conductor as well as through a braided conductor connection to the switch handle mechanism. Include a provision for locking ground accessible switch handles in the open and closed position.

Single-pole knife blade switches and copper barrels inside distribution cutouts are only acceptable for use in locations where frequent switching is not expected.

3-10.6 Surge Arresters.

Provide surge arresters on the line side of:

• Pole mounted transformers.

• Overhead to underground terminal poles.

• All “normally open” switch ways of pad-mounted sectionalizing switches connected to and served from overhead lines.

• Underground primary metering installations connected to and served from overhead lines.

Provide surge arresters on the line and load sides of:

• Gang operated airbreak switches on overhead lines.

• Primary metering applications on overhead lines.

• Recloser/sectionalizer applications on overhead lines.

3-10.7 Fuse Protection.

Provide IEEE C37.41 rated backup current limiting fuses in series with Type K expulsion fuses on systems that are:

• Greater than 15 kV.

• 15 kV and lower that have available fault currents equal to or greater than 7,000 asymmetrical amperes.

Note: Existing systems should continue to use the expulsion fuse link type that represents the standard for that system.

3-10.8 Automatic Circuit Reclosing.

Do not provide automatic circuit reclosing on underground distribution circuits. \2\

3-10.9 Sectionalizer.

Comply with IEEE C37.63. Use sectionalizer as a not load break switch in conjunction with an upstream recloser or circuit breaker. It counts the interruptions created by a

Change 3, 01 November 2019 recloser during a fault sequence. On a preset count, the sectionalizer trips during the dead time of the upstream recloser and isolates the faulty network section.

Note: Sectionalizer with a separate Controller requires an auxiliary power source.

Sectionalizer with an integral electronic control incorporates electronic logic and trip circuits which are controlled and powered by current transformers. /2/

3-10.10 Ground Connections.

\2\ All pole mounted equipment and metallic frames must have two connections to the multi-grounded system neutral conductor. /2/ Keep ground wires straight and short.

Minimize bends in all ground connections.

3-11 UNDERGROUND ELECTRICAL SYSTEMS.

3-11.1 Underground Distribution General Criteria.

3-11.1.1 Locations.

Provide underground distribution as follows:

• In areas where the primary distribution is already underground.

• In locations where overhead distribution is operationally hazardous, such as within airfield clearance zones.

• As required to supply pad-mounted equipment and transformers.

• Near electronics or munitions facilities that have clearance requirements for overhead power lines.

• Near piers and loading areas where overhead cranes operate.

• In congested industrial areas.

• In areas where storm and hurricanes or typhoons can damage overhead distribution.

3-11.1.2 Conductor Type.

Due to the increasing technology improvements with aluminum conductors and connectors and the economic disadvantage of providing copper conductors, provide aluminum conductors for new underground lines and extensions of existing circuits.

This includes all new medium voltage system designs that do not require interface (splicing copper to aluminum in underground structures) with existing copper infrastructure. Provide only copper grounding electrode systems. The use of copper conductors is authorized for extensions of existing systems in which the use of aluminum results in technical limitations, such as:

• Maintaining required circuit ampacity, including derating associated with number of circuits in a common ductbank or burial depth.

Change 3, 01 November 2019

• Maintaining base infrastructure capacity, including feeder cross-tie capability.

• Conduit size. All phases are required to be installed in the same conduit.

• Undersized or congested structures necessitating tape splices of aluminum cable to existing copper cable. Note: If adequate space exists for the use of improved technology “heat shrink or cold shrink” splices, or if proper aluminum to copper compression connectors designed for the natural offset of size difference between the conductor materials is available as a standard manufactured product, provide the copper to aluminum cable extension.

Approval of copper conductors is authorized as follows:

• For the Navy, the Facilities Engineering Command (FEC) organization’s chief engineer has the authority to use copper product for applications within their applicable jurisdiction, in addition to the above authorized use for extensions.

• For the Army, the Installation Department of Public Works Chief Engineer has the authority to use copper product, in addition to the above authorized use for extensions, within their applicable jurisdiction if documented in the planning process and the design analysis.

• For the Air Force, the Base Civil Engineer has the authority to exercise the criteria option of copper product, in addition to the above authorized use for extensions, within their applicable jurisdiction if documented in the planning process and the design analysis.

3-11.1.3 Routing.

Do not route primary underground utilities under buildings. Do not route systems greater than 600 volts under buildings except as a direct service entrance to a single interior transformer.

3-11.1.4 Marking and Labeling.

Tag all underground cables in all accessible locations such as in manholes, transformers, switches and switchgear. Install a detectable locator tape above all buried underground circuits. Marking must meet the base utility standards.

3-11.2 Ductbanks.

The definition of the terms ductbank, conduit, and duct are often confused. Within this UFC, a ductbank consists of two or more conduits (or ducts) routed together in a common excavation with or without concrete encasement.

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3-11.2.1 Conduit Size.

Minimum conduit sizes must be as follows:

• Provide concrete encasement for primary distribution conduits between underground structures, and between underground structures and associated equipment, except in locations where soil conditions prohibit a stable environment. With approval of the Activity, utilize directional boring where conditions are not conducive to concrete-encased ductbanks.

Primary Distribution Conduits (along main run and on laterals between underground structures and associated equipment) – size as needed to satisfy conduit fill and jam ratio criteria for the selected conductor size and voltage class, with 5 in (127 mm) minimum. For primary distribution conduits serving Navy dockside utilities, provide 6 in (155 mm) minimum.

Secondary Distribution Conduits (Low Voltage) – size as needed to satisfy conduit fill and jam ratio criteria for the selected conductor size, with 4 in (103 mm) minimum for conductor sizes 500 kcmil and larger. In this case, secondary distribution conduits refer to the low voltage conduit routing from the distribution transformer to the service entrance equipment. This requirement does not apply to street lighting circuits, secondary supplies to housing, or secondary circuits originating from an interior panel.

• Telecommunication Conduits – 4 in (103 mm) for main telecommunications circuits.

Specialty telecommunications circuits, such as cable television or alarm circuits, can select conduit sizes as needed for the application.

Example: a cable television circuit might only require a 2 in (52 mm) conduit stubbed out to a fiberglass composite handhole.

3-11.2.2 Installation.

• Use Type EB Schedule 20 PVC conduits (minimum thickness) for conduits installed in concrete encasement. Provide at least 3 in (75 mm) of concrete encasement.

• Use Schedule 40 PVC conduit (minimum thickness) for conduits that are not installed in concrete encasement.

• Install all phase conductors and neutral conductor, if applicable, in the same conduit for three-phase circuits and delta-connected single-phase circuits. Note: some utilities install each phase conductor in a separate conduit. This practice is not authorized.

• Bury conduit at a minimum depth of 18 in (450 mm) below grade.

Conduits must be 24 in (600 mm) minimum depth under roads and

Change 3, 01 November 2019 pavement, and for voltages between 22 kV and 40 kV. Apply conductor ampacity derating when exceeding the NFPA 70 maximum burial depths.

• Provide 3 in (75 mm) clearance between conduits utilizing interlocking plastic spacers.

• For primary distribution circuits, provide spare conduits such that at least 1/3 of the ductbank contains empty conduits with a minimum of at least one spare conduit.

• For secondary distribution circuits on the secondary side of distribution transformers, provide one spare conduit.

• Include pull wires (pull string or pull rope) in all spare ducts.

• Provide a transition from Type EB conduit to Schedule 40 PVC conduit before emerging from underground.

• Use directional boring or jack-and-bore techniques for routing conduit(s) under existing pavement for roadways, aircraft aprons, runways and taxiways. Directional boring can be used for other locations where excavation can adversely affect daily operations.

Note: Comply with Appendix B for the use of directional boring for conduit installations.

• For permafrost locations, use ductbank installation methods that are the standard for the base, post, or local utility.

3-11.3 Direct Buried Wiring Methods.

The term direct buried wiring refers to the direct burial of conductors without any conduit or concrete encasement. Comply with IEEE C2 for all direct burial systems.

3-11.3.1 Authorized Locations.

With approval of the Activity, direct buried wiring methods for low or medium voltage systems may be allowed for specific applications such as:

• Special applications in remote or extremely controlled areas. Examples of such applications could be ranges or range facilities, renewable energy projects such as wind farms or bulk photovoltaic (PV) facilities provided for the purpose of supplementing system demand loading.

• Housing projects utilizing residential type distribution principles of single-phase, pad-mounted transformer designs and single-phase distribution principles for balanced three phase system loading.

• Bulk power transfer (feeder) from point to point crossing remote or controlled real estate which will revert to public utility ownership and maintenance upon completion.

Change 3, 01 November 2019

Direct buried wiring methods are not authorized for any application which constitutes a part of the base utility core distribution infrastructure.

3-11.3.2 Conductor Type.

All approved direct burial medium voltage systems can utilize concentric neutral underground distribution cable design instead of the typical Type MV tape-shielded conductor design utilizing a separate 600 volt insulated neutral conductor.

3-11.3.3 Crossing of Paved Areas.

Provide a spare conduit system with associated enclosures for direct buried systems under all streets, roads, and parking areas to provide for future maintenance capability without having to disrupt pavements. Provide minimum Schedule 40 PVC extending 5 feet on each side and capped for future use.

For crossing existing paved areas, the directional boring technology referenced in the paragraph titled Directional Boring, also applies for installation of the direct buried system.

3-11.4 Directional Boring.

Directional boring (DB) is a trenchless technology method to install high density polyethylene electrical (HDPE) conduit used for underground electrical distribution systems.

3-11.4.1 Authorized Locations.

Do not select DB methods as an installation means in lieu of concrete encasement or other approved jack-and-sleeve techniques, based solely on cost. Concrete encasement and jack-and-sleeve techniques always provide the best means to protect conduit and conductors; therefore, DB is authorized only for crossing under the following:

• Roads.

• Parking lots.

• Airfield aprons, taxiways, or runways (not airfield lighting circuits due to counterpoise requirements).

• Bodies of water.

• Environmentally sensitive areas with appropriate federal, state, and local government approval.

• Historical preservation areas with appropriate federal, state, and local government approval.

DB is also authorized for locations where earth setting has caused shearing of conduits.

Document this basis for selection of DB as part of the design analysis.

Change 3, 01 November 2019

3-11.4.2 Limitations.

DB is applicable to medium-voltage (MV) underground distribution systems between 1000 volts (V) and 34.5 kilovolts (kV) (nominal) and all low-voltage distribution systems (less than 1000 V). It is not applicable to airfield lighting circuits. Use of DB techniques to install electrical conduit distribution for voltages greater than 34.5 kV (nominal) is prohibited.

Refer to Appendix B regarding depth of DB. The depth can be less if a detailed survey is performed and documented before starting boring.

3-11.5 Underground Structures (Manholes and Handholes).

3-11.5.1 General Requirements.

Provide separate power and communication manholes. When power and communication duct lines follow the same route, use a common trench and locate power and communication manholes in close proximity to one another and staggered.

Use manholes for main duct runs and wherever shielded medium voltage cable is installed. For the Air Force, pad-mounted sectionalizing termination cabinets can be used instead of manholes for locations that do not have multiple feeders.

Handholes can only be used for airfield lighting circuits, for other non-shielded medium voltage circuits, and for low-voltage and communication lines.

3-11.5.2 Equipment Prohibited Inside Manholes.

The following equipment is prohibited inside underground structures:

• Load junctions.

• Separable splices (bolt-T connections).

• T-splices and Y-splices on systems rated for greater than 15 kV.

• For the Air Force, T-splices and Y-splices on all medium voltage systems.

• Power distribution equipment, including transformers and switches.

3-11.5.3 Splice Locations.

All in-line splices must be in underground structures. Do not use handholes for splicing shielded power cables.

3-11.5.4 Fireproofing.

Ind…