Section 8 Underground Service and Installations
8.1 General Comments
Economic, physical and technical considerations normally dictate the use of overhead distribution facilities in the Department’s operating area. In some circumstances, however, it is feasible and practicable for the Department to install portions of its distribution facilities underground. In other circumstances, the value to the property owner(s) of having the electric distribution and service facilities installed underground outweighs the added costs to install them. Therefore, circumstances may exist where the Customer may either elect or be required to take electric service through an underground service from an overhead or underground distribution system. In such cases, the Customer will be required to pay the additional cost, if any, in excess of the cost of an overhead system. In all cases where the Customer desires service from underground conductors, the Customer should consult the Department.
All new residential subdivisions developed will be served by underground distribution systems and secondary services unless otherwise specified by the Department. Also, all services that require more than 320 amps shall be underground services.
Single phase underground service will normally be 120/240 volts, three wire. The service from three phase pad mount or vault type transformers should be restricted to 208Y/120 or 480Y/277 volts, four wire. The Department’s typical installation includes a pad mount transformer. Occasionally, other type transformers may be required. Consult the Department for details.
All conditions covered in Section 6 must also be met in addition to the conditions specified in this section.
8.2 Ownership of Facilities – Residential
The line side terminals where the Department’s wire is attached in the Customer’s metercan shall be the demarcation point between facilities owned by the Department and facilities owned by the Customer. The exception to this rule is the meter that is installed on the Customer side of the point of attachment and the conduit run from the utility pole to the metercan. The meter is owned and serviced by the Department even though it is attached in the meter can that the customer owns. The customer owns the conduit that runs from the utility pole to the metercan. See Drawing.
8.3 Ownership of Facilities – Commercial and Industrial
The load side terminals where the Customer’s wire is attached in the Department’s transformer shall be the demarcation point between facilities owned by the Department and facilities owned by the Customer. The exception to this rule is the meter that is installed on the Customer side of the demarcation point. The meter is owned and serviced by the Department even though it is attached in the meter can that the customer owns. See Drawing.
8.4 Agreement for Underground Service
The Customer may be required to execute an agreement which will set forth ownership and maintenance responsibilities, characteristics of the services
covered, and any financial arrangements. An agreement may also be required with the individual Customer in order for the Department to provide underground service.
8.5 Specification Requirements
All facilities which the Department will own and operate shall be installed either by the Department or to the Department’s specifications. The Department will not accept ownership of any underground facilities that do not meet the Department’s specifications.
8.6 Requirements for Obtaining Underground Residential Service
8.6.1 General Comments
Underground residential service may be available from either overhead or underground facilities. The Customer shall provide, install, own and maintain the conduit from the meter socket down to a point thirty inches (30″) below ground in accordance with Department specifications. (Note: This will require the use of a 36” bend.) See Drawing. Installation of the conduit around or through the footings shall conform to the requirements of authorities having jurisdiction. Consult the Department for information if conflict arises.
Should the Customer request underground service with a complete conduit system, the Customer shall provide a continuous run of conduit with a minimum size of 2″ for 200 ampere service. See Drawing. Drawing shows conduit encased in concrete when such an installation is required. Consult the Department for details. The Department shall furnish, install and maintain the underground conductors in the conduit system. Refer to Section 8.9, Conduit, for more information.
| MAIN SIZE | CONDUIT SIZE | SCHEDULE |
| 200 amp | 2 inch | 40 |
| 320 amp | 3 inch | 40 |
| 400 amp | 4 inch | 40 |
8.6.2 Underground Electric Service for New Residential Subdivisions
Contact the Department at the earliest date possible so that:
- The Department can plan the distribution system, design any applicable street lighting feed points or other lighting systems, determine the meter and service locations, and
- Agreement can be reached on the manner of paying the additional cost, if any, in excess of the cost of any overhead system.
NOTE: The Department must have a 10’ right-of-way and access along public streets in order to build and maintain street lights, control equipment, and conductors for street light circuits. In the case of private roads, for example roads in gated communities, street lights are the responsibility of the property owner(s) and/or the communities that they are installed in. The Department cannot build or maintain privately owned street lights.
Underground facilities will be installed on the front lot easement with pad mount transformers. Easements for underground facilities shall be described on Department’s right-of-way agreement forms and furnished to the Department as outlined by Department policy and/or on dedicated recorded plat. Refer to Section 6.2, Right-of-Way for Service Facilities.
Customers within an underground subdivision adjacent to an overhead distribution system may be served with an underground service from the overhead system.
8.6.3 Underground Service From An Underground Distribution System
A residential Customer may elect or be required to take electric service through an underground service from an underground distribution system and will be required to pay in some manner the additional cost, if any, in excess of the cost of an overhead system.
8.6.4 Underground Service From Overhead Distribution System
The Customer may elect or be required to take service through an underground service from an overhead distribution system and will be required to pay in some manner the additional cost, if any, in excess of the cost of an overhead service.
New customers in new residential areas taking underground service will be required to pay the additional cost, if any, in excess of the cost of an overhead service. The cost of the underground service is the installed cost of the cable plus conduits, and handholes, if required. In general, a handhole is not required when a customer is taking underground service from an overhead system. Handholes are normally required when two or more customers are taking underground service from the same pole in an overhead distribution system. Two or more conduits may be installed in accordance with the limitations in the Section 8.9.2.1, Conduit Installation General Comments, with the approval of the Engineering Design Supervisor. The conduit for the pole shall be provided by the Customer and installed by the Department. The elbow at the base of the pole and adjacent to the house shall be provided and installed by the Customer. Refer to Section 8.9.2.2, Conduits Used In Residential Underground Installations. The cost of the handhole and riser installation may be divided among the Customers to be served or paid for by the Developer.
8.6.5 Underground Service Replacing Existing Overhead Service
An existing Customer served with an overhead service may request the removal of the overhead service and installation of a new underground service. The Customer is responsible for paying the total installed cost of the new underground service. Consult the Department for information and specifications.
8.7 Requirements for Commercial, Industrial, and Other Non-Residential Underground Service
8.7.1 Underground Service From Underground Systems
Underground secondary service from an underground distribution system may be provided to non-residential Customers. In general, the Customer will be required to install, own and maintain all conduit and conductors on the load side of the transformer from which service is being provided. Unless approved by the Department, these conductors must be copper and must not exceed 500 MCM in size. It is the responsibility of the Customer to install, own, and maintain the transformer pad or vault. This includes both single and multi-meter installations. See Drawing.
Any underground primary conductors required to serve the Customer will be owned by the Department. The Customer shall pay the difference between the cost of the Department’s underground facilities and the cost of the Department’s overhead facilities, if any, to serve the load. Refer to Section 8.9.2.3, Conduit Used In Commercial, Industrial, and Other Non-Residential Underground Installations, to Section 8.10.3, Conductors Used in Underground Non-Residential Installations, and to Section 8.13, Transformers Used In Underground Installations. Consult the Department for additional information, specifications, and contract forms for underground installations.
8.7.2 Underground Secondary Service From Overhead Systems
Underground secondary service from an overhead distribution system may be provided to non-residential Customers. In general, the Customer shall install, own and maintain the conduit and conductor system beginning at the secondary terminals of the transformer. The Department will install any Customer owned conduits and conductors to be attached to its poles. Replacement of Customer owned facilities on Department owned poles shall be at the Customer’s expense. Refer to Section 8.9, Conduit and Section 8.10.3, Conductors Used in Underground Non-Residential Installations. Consult the Department for additional information, specifications, and contract forms for underground installations.
8.8 Underground Electric Service for Mobile Home Parks
The Department will provide underground electric service to approved Mobile Home Parks. The Customer shall pay the difference between the overhead and the underground systems. Refer to Drawing for typical layout for underground served Mobile Home Park. (Approved Mobile Home Park shall mean one that is permanent, rather than temporary, and must have permanent central water and sewage systems.)
Service to individual mobile homes will be made by individually installed meter pedestals. The Customer shall supply the pedestal. Consult the Department for information.
The Department may supply service to a Customer owned street lighting system or supply lighting under the appropriate lighting rate where applicable.
8.9 Conduit
8.9.1 General Comments
The conduit may be rigid/ intermediate metal steel, rigid aluminum, or Schedule 40 PVC in appropriate applications. All conduits shall be of such size and type to meet the requirements of the Department and the Department specifications for the selected cable to serve the Customer. The Customer’s anticipated future load requirements should also be considered when sizing cable and conduit to serve the Customer’s present requirements.
8.9.2 Installation of Conduit
8.9.2.1 General Comments
All conduit must be installed according to Department requirements. Normally, conduits on a Department owned pole will be limited to one per customer. More than one conduit per customer may be allowed in certain circumstances, with prior Department approval. A maximum of two conduits may be attached to a Department owned pole if the sum of the two conduit sizes does not exceed ten inches. A maximum of three conduits may be attached if the sum of conduit sizes does not exceed seven and one half inches. Customers requesting more than the allowed number of conduits may be required to provide a separate support structure for the conduits and a suitable attachment point for the Department owned overhead service conductors. When more than one conduit is allowed, they shall be installed adjacent to each other, and not cover more than one quarter of the pole circumference.
Due to the quality of the soil in some portions of the NLRED service area, concrete around the conduit may be required. If concrete encased conduit bends are required at the base of the pole, the concrete must be formed to prevent its touching the pole and a fibrous separator is required between the pole and the concrete.
8.9.2.2 Conduits Used In Residential Underground Installations
Services installed in conduits for residential customers shall conform to Drawing S-5. The Customer shall install the conduit to the base of the pole. The conduit shall be installed such that it has no more than two 90 degree bends, including riser bends, (riser bends shall be 36 inches in radius), . In all cases where the run is of a length greater than 100 feet, a pull box shall be installed by the Customer as advised by the Department. In no case shall the conduit run exceed 100 feet without the prior approval of the Department. The pull box shall be of a design that conforms to Department specifications.
The Customer shall supply the conduit riser in accordance with Department specifications. The Department will install the riser on the pole. The Department will pull the conductors in the conduit system. Once installed, the Customer will own all the conductors and the conduit up to the elbow at the service pole (in the case of a riser) or to the elbow entering the padmount transformer that is serving their property.
When two or more services originate from one Department pole having overhead facilities, means of accommodating multiple services may be required by the Department.
8.9.2.3 Conduit Used In Commercial, Industrial, and Other Non-Residential Underground Installations
The proposed load, cable sizes and conduit sizes should be given consideration when determining the pulls and lengths of conduit run. The number, design and location of pull boxes and total length of conduit runs to be installed shall be specified by the Department. If pull boxes are required, they shall be of sufficient strength, as approved by the Department, to support all expected loads that may be imposed on the structure, including local traffic. All spare conduits, if necessary, will conform to the requirements set forth in Section 8.9.4, Spare Conduits. See Drawing (we don’t have a drawing for this) for a typical primary service to a single pad mount transformer serving commercial or industrial Customers. In general, all service wire and conduit is owned by the commercial, industrial, or other non-residential customer. Table 8.9-3 contains a recommended conduit guide for approved conductor sizes.
Table 8.10-3: Typical Underground Primary and Secondary Conductor and Conduit Guide
| Conductor Size | Number of Cables | Recommended Conduit Size* | Maximum Pulling Length | Elbow Radius |
| #1/0 AL – (15 kV) | 1 | 2” | 300’ | 36” |
| #1/0 Cu – (15 kV) | 1 | 2” | 300’ | 36” |
| #1/0 Cu – (15 kV) | 3 | 4” | 300’ | 36” |
| 750 AL – (15 kV) | 3 | 5” | 300’ | 36” |
| Secondary Conductors | ||||
| #1/0 AL Triplex | 1 | 2” | 100’ | 36” |
| #4/0 AL Triplex | 1 | 2” | 100’ | 36” |
| #350 AL Triplex | 1 | 3” | 100’ | 36” |
*The recommended conduit size conforms to the Department standards for conduit used on the Department system. Consult the Department during the design process to ensure that the proposed conduit system meets Department requirements.
8.9.3 Types of Conduit
8.9.3.1 General Comments
All conduits shall be PVC, rigid/intermediate metal steel, rigid aluminum, and/or rigid nonmetallic conduit with a U. L. label. Local Building Codes may be restrictive in the type(s) of conduit permitted. Consult authorities having jurisdiction before choosing conduit material.
8.9.3.2 Rigid/Intermediate Metal Conduits
Rigid intermediate metal steel and rigid aluminum conduits (with a U. L. label) may be used. Rigid aluminum conduit (with a U. L. label) can be used above grade only. In certain cases, when steel conduit is used below final grade, it must be completely encased in a minimum of 4″ of concrete according to Drawing S-9 or wrapped with a material approved by the Department to provide corrosion protection.
8.9.3.3 Rigid Nonmetallic Conduits
Rigid Polyvinyl Chloride (PVC), Schedule 40, (with a U. L. label), may be used as a conduit riser, where building codes permit, under the meter enclosure, and as primary, secondary, and service risers on distribution poles. Rigid nonmetallic conduits may be used in inaccessible areas and below final earth grade. Generally, nonmetallic conduit installed below grade must be at least Schedule 40 PVC (with a U. L. label). In certain cases, concrete encasement may be required according to Drawing S-9.
8.9.3.4 Conduit Fittings
Conduit fittings to join the continuous lengths of conduits and to join the continuous lengths to bends of the same material shall be of the same material as the conduits and shall be U. L. approved and meet Department specifications. Fittings to join rigid nonmetallic conduit to rigid metal or intermediate metal conduit at transitions such as from below grade to above grade shall be U. L. approved and meet Department specifications.
8.9.4 Spare Conduits
In some cases, the Department may recommend the installation of spare conduits. Spare conduits will conform to all conduit requirements as set forth in these Service Standards.
8.10 Conductors
8.10.1 General Comments
The Department will generally own and operate all conductors on the Department side of the point of delivery. If the Department’s facilities do not exist to serve the Customer’s load, the Customer shall be required to pay for the difference between the cost to extend the line as an overhead distribution facility and the actual cost to install underground facilities. Specific requirements are defined in the Department’s line extension policy. Consult the Department for details.
8.10.2 Conductors Used in Underground Residential Installations
Normally conductors installed for permanent service to single residences shall be 3/0 aluminum. Consult the Department should some other size conductors be desired. Installations using conduits shall conform to Section 8.9.2.2, Conduits Used In Residential Underground Installations.
8.10.3 Conductors Used in Underground Non-Residential Installations
Commercial, industrial, and other non-residential Customers will install, own, and maintain all secondary conductors starting at the secondary side of the transformer. The conductors shall be copper and shall be no larger than 500 MCM in size. Normally, a maximum of eight conductors per phase per transformer will be permitted. Bus duct may be required for loads which exceed eight conductors per phase. The Department will make all secondary connections.
8.11 Termination of Conductors
8.11.1 General Comments
The term “terminals” refers to NEMA flat pads. They shall be aluminum bolted terminals on aluminum conductor and shall be either bolted aluminum or bolted flow tin plated copper terminals on copper conductor. The secondary connectors shall be provided by the Department. When the Customer makes connections of terminals to terminals, they must use the necessary bolt assemblies that meet Department specifications. Two hole NEMA terminals are required for conductors up to and including 1000 kCM and must fit side by side on a four hole NEMA terminal. Four hole NEMA terminals are required for all conductors larger than 1000 kCM. All terminals must be installed according to Department specifications. Connectors provided in Department approved meter enclosures may be bolted type suitable for bolting both aluminum and copper conductors.
8.11.2 Termination in Pad Mount Transformers
The Department shall furnish terminals for Customer installed and owned secondary conductors. Terminals must conform to Department specifications as outlined in Section 8.11.1, General Comments, and must be installed according to Department specifications. The Department shall bolt all terminals to the connectors of the transformer. The phasing and proper conductor length will be the responsibility of the Customer regardless of who installs the terminals or bolts the terminals to the transformer connectors.
8.12 Metering for Underground Service
Generally, the meter installation shall be located outside of a building or structure. Refer to Section 11.5, Location of Meter Installations. Disconnect switches or a main breaker panel shall be mounted to the side of the meter enclosure. Prior approval must be obtained from the Department for the installation of any service equipment directly below the meter enclosures.
If a single metering installation is to be used in connection with a three phase pad mount transformer installation, the meter shall be installed on unistrut supports next to and not in the transformer pad. The metering can shall not be attached directly to the transformer. Installing the meter can on the building is allowable as long as the meter can is within 25’ of the transformer.
Special metering options may be available with approval of the Department. The Customer shall bear the additional cost made necessary by the special metering options.
8.13 Transformers Used in Underground Installations
8.13.1 General Comments
The Department will generally own and operate all transformers on the Department side of the point of delivery. Pad mount transformers shall be installed in accordance with Department specifications. Vaults, enclosures, etc., when used, will beat Customer’s expense and shall conform to Department specifications. See Section 10, Transformers Vaults and Substations. Consult Department for specific details.
8.13.2 Transformer Pads or Slabs
Transformer pads or slabs shall be provided by the Customer, and will conform to Department specifications. The Department will specify the type of supporting foundation that is needed for the transformer installation when the pad or slab is owned and/or installed by the Department.
The specifications to the transformer pad will be provided to the Customer upon completion and submission of the Customer’s load sheet to the Department. Please consult the Department for further details.
In cases where the primary system is three phase and radially fed, a minimum of one spare elbow shall be installed with the primary conduit in the transformer pad or slab when a complete spare conduit system is not provided.
