Underground Service Philosophy
What is MTEMC's philosophy regarding underground service?
MTEMC and virtually all other electric utilities build to an overhead standard as the most cost-effective type of construction. We are open to putting lines underground provided the additional cost is covered by or for the user. Overhead service was established as the standard construction because over time it has been the most cost-effective design. When alternatives like underground service are requested by developers or mandated by cities, the customer benefiting from the alternative design pays the additional cost.
What are the strengths and weaknesses of overhead and underground service that affect performance and reliability?
Overhead facility damage is easier to locate than underground and can generally be repaired quicker.
Underground interruptions may be less frequent, but typically last longer due to more complex repair requirements. Damage and corrosion of underground electrical systems often shows up days or even months later, causing additional outages and inconvenience to customers.
Storm winds can damage both types of systems causing outages. Overhead systems face outages resulting from trees and debris blowing into lines. Underground systems face outages from trees collapsing on above-ground transformers and switch boxes or from tree root systems uprooting buried cable when trees topple.
Also, while a neighborhood may be locally served by underground cable, all electric service eventually comes back above ground and connects to overhead service, either in the neighborhood next door, or further down the street where overhead main lines and transmission lines move power from power plants and substations into our neighborhoods. Thus, exposure to above ground electric service from weather, animals, and trees is never fully eliminated.
Why is there a differential cost for new underground service?
It is the position of MTEMC, TVA and virtually the entire electric industry, that it would be unfair to charge all customers a higher price to cover the cost of new undergrounding, since not everyone would get the benefit nor necessarily be willing or able to pay the higher cost.
Why must the customer or requesting party pay for the conversion from overhead to underground?
Similar to new service requests for underground, conversions take into account the requirement that MTEMC provide electric service to all its customers in the most cost-effective manner available and this is typically an overhead system.
In order to ensure customers throughout our service territory are being treated fairly and that customers in one area are not subsidizing underground facilities being built or converted in another area, MTEMC's policy is that the party seeking a conversion from overhead to underground facilities must pay for the associated cost of conversion.
But I live in a development with underground service and I didn't pay anything extra ? how is that?
You may not realize it, but you did. For aesthetic reasons, many developers contract with MTEMC to bury their lines when they are laying out a new neighborhood. Thus the added cost for underground service and other community amenities is typically included in the price you pay for a new home.
What are some specific costs associated with converting individual overhead service to underground?
The costs can vary widely and depend on variables such as:
Whether local government requires electrical installation or wiring to be upgraded as part of your conversion.
Whether an electrician will do the work to dig and backfill the trench needed to bring the underground facilities from the easement to the building.
The length of trench that's needed to accommodate the conversion.
Whether the existing overhead "weatherhead" extends through the roof of the building, in which case you may need to incur the cost of roof repair as well as paint and aesthetics.
These costs and arrangements are separate from the work MTEMC would handle and are the responsibility of the customer, just as they would be in seeking to convert from a septic tank to a sewer system or other similar efforts.
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Why must some of the equipment in an underground system remain above ground?
While conduit and cable can be placed underground, which eliminates poles and wire, transformers and switch cabinets need to be accessible to MTEMC crews at ground level for timely maintenance, outage repairs, rerouting power and other functions.
What might it cost to convert from overhead to underground service?
The two key drivers contributing to the cost calculations are labor and materials. Depending on these factors, underground facilities can cost anywhere from $500,000 per mile to more than $4 million per mile.
What makes it so much more expensive to do conversions versus new construction, especially considering that the customer pays for most of the peripheral work?
In conversions, MTEMC's costs are significant. The work includes building a whole new system, while operating the existing service and then dismantling the existing service once the new one is up and running. The higher costs also reflect the fact that conversions in older neighborhoods have a lot of issues associated with working in and around and avoiding impacts to other utilities such as phone, cable, sewer, gas lines, water lines, etc. Finally, all new underground components must be acquired and installed, including conduit, cable (wire), pad-mounted transformers and switch cabinets. Additionally, shared main line work is usually required, which is even more costly than converting individual service and neighborhood lines. Typically, as a percentage of cost, dismantling runs about 15 percent, installing underground components about 65 percent, and actual excavation about 20 percent.
What are some of the impacts associated with converting an older overhead system to new underground?
The logistics of converting an existing grid system in an established neighborhood can be considerably more expensive and disruptive to personal property and surroundings than, for example, building new.
For example, utilities often share poles above ground, so that if the objective is to move utilities underground, it's not just electrical service that needs to be considered, but also phone, cable television and Internet service. This then presents additional considerations, such as different spacing requirements, boring and/or trenching needs and ground-level switching boxes involved in providing each type of service.
Driveways, sidewalks, fences, landscaping, sprinkler systems and yards may need to be torn up or may be inadvertently damaged if not clearly delineated. Ingress and egress to homes and business could be impacted for extensive periods of time.
Because permits are needed to change meter-related equipment, conversions in older homes and neighborhoods may end up triggering city or county requirements that homeowners/businesses bring interior wiring up to current code. This could require the expense of a licensed electrician and potentially extensive interior rewiring and remodeling.
Finally, legal easements are needed from all conversion participants that allow MTEMC access to its underground equipment, including the above ground components ? and a number of people must agree to have the large green transformer box and pad or other switching boxes in their yards.
What will it cost to bury the other utilities such as telephone and cable television?
This question must be addressed by those utilities.
What are some examples of instances where proposed overhead to underground conversions would not be feasible?
Instances in which private property owners aren't willing to provide easements necessary for MTEMC to design and engineer the conversion.
Locations where necessary safety standards and operational clearances cannot be met, for example extremely congested areas where switch cabinets cannot be installed with sufficient operating clearances.
Areas prone to flooding. (Excessive flooding can short out transformers, which then cannot be safely restored until flood waters recede.