Undergrounding Overhead Lines FAQs

What is undergrounding?

How does the undergrounding of overhead wires help improve reliability?

How does replacing existing underground cable in a subdivision help improve reliability?

How does installing more cable in an already underground subdivision help improve reliability?

How does undergrounding an overhead line that is not in my neighborhood help reduce my power outages?

Why must some of the equipment in an underground system remain above ground?

What does an underground system look like?

Why does AmerenUE install new underground systems in front lots? Why not place them in the back yard where many overhead poles are located?

Why would some poles have to remain after an overhead line is placed underground?

What are some examples of instances where proposed overhead to underground conversions would not end up being feasible?

What is involved in having the service wires to my house placed underground? What would I have to do myself?

Can you be more specific about some of the costs in converting my individual overhead service wires to underground?

1.

Q.

What is undergrounding?

A.

Undergrounding is the act of replacing a system of overhead wires with an equivalent system of underground cables that are pulled through buried plastic pipes. The photos show examples of spans of AmerenUE overhead wires. Generally two to six wires are supported by a pole. The “high voltage” wires are those highest on the pole, while the “low voltage” wires are situated below them.    Overhead wires like these represent some of the greatest threats to electric service reliability, especially in heavily treed areas. If a tree or limb makes contact with or damages any of these wires in any location along their route, customers by the dozens (or hundreds) could lose their electric service. And because electricity travels a great distance to reach your house, undergrounding projects that are blocks or even miles away from your home can still improve your service reliability.

2.

Q.

How does the undergrounding of overhead wires help improve reliability?

A.

Most of the power outages experienced during severe weather are due to trees or tree limbs falling onto the lines. This can cause the wires themselves to break or even cause nearby poles or equipment to fail. Undergrounding overhead electric lines drastically reduces the exposure of these wires and equipment to the effects of trees, wind, ice and other severe weather conditions, thus reducing the number of outage events. It is important to understand, however, that no level of undergrounding will completely eliminate outages.

3.

Q.

How does replacing existing underground cable in a subdivision help improve reliability?

A.

The type and vintage of underground cables, along with the physical conditions in which they exist and operate, are factors in how reliably they supply electricity to customers in residential subdivisions. Given the updated technology available with AmerenUE’s new cables and improvements that have been made in how they are installed, the replacement of existing underground cables (especially those that have been repaired many times over) can help reduce the number of power outages due to cable failures.

4.

Q.

How does installing more cable in an already underground subdivision help improve reliability?

A.

When AmerenUE serves a new underground subdivision in Missouri today, we do so with two separate lines that can be connected together and switched back and forth when one of them fails. However, some older underground subdivisions have only one line serving them. When outages occur in these locations, we are unable to switch to an alternate line, and power can’t be restored until the actual damage is repaired. By having a second underground supply available in these subdivisions, the duration of outages can be significantly reduced by merely switching affected customers to it and repairing the damage later.

5.

Q.

How does undergrounding an overhead line that is not in my neighborhood help reduce my power outages?

A.

Electric power lines operate in a similar manner to the electrical wires in your house. The wires in your house are located in the different rooms in order to supply electricity to them, and they all come together at the “fuse” or “circuit breaker” box. When a problem occurs in one room of the house, the fuse or circuit breaker “trips,” interrupting power to perhaps a number of different rooms, while allowing power to continue in the rest of the house. Similarly, AmerenUE’s power lines come together at main lines that have their own fuses or circuit breakers. When an overhead line is damaged due to trees limbs falling onto it, this causes the fuse or circuit breaker to “trip,” interrupting power to customers not only on that damaged section, but to all customers “downstream” of that fuse or circuit breaker. Undergrounding the overhead lines in a particular area will not only reduce the number of outages to the customers in the immediate vicinity, but also to all those customers “downstream” of the fuse or circuit breaker.

6.

Q.

Why must some of the equipment in an underground system remain above ground?

A.

The installation of buried plastic pipe and underground cable is what makes the removal of poles and wires possible, and the new cable is not visible after it’s been installed. Some undergrounding equipment, however, has to remain above ground so AmerenUE personnel can have access to critical components. For example, transformers and switch cabinets need to be accessible to crews at ground level for timely maintenance, outage repairs, re-routing power, and other tasks.

7.

Q.

What does an underground system look like?

A.

The most common components of an underground system that are above ground and visible to the eye are padmount transformers, service pedestals and terminal poles. Transformers are devices that take the high voltages on AmerenUE’s spans of overhead wire and reduce them to the safer, more usable levels that are seen inside homes and places of business.    An overhead transformer (right photo) is a gray cylindrically-shaped metal “tank” that is fastened to the pole and has several overhead wires connected to it.    The underground equivalent of this is the padmount transformer (photo below), a “forest green” colored box. In residential areas, the transformer’s dimensions are roughly 32” tall x 34” wide x 34” deep. All cables come into the transformer from below ground, and all the connections are made inside and kept out of view.

The locations of padmount transformers need to be close enough to streets, parking lots or other “improved” surfaces so that installation and maintenance can be performed using trucks sitting on those surfaces. In residential areas, this places the transformer in front, roughly 15 to 20 feet from the street. It is usually installed along the property line between adjacent lots. This location will help prevent damage to private property by heavy equipment.

The photo at right shows how a set of low voltage overhead connections appears on a pole. These connections are necessary to distribute the low voltage lines from a single overhead transformer to each home and business that it serves.    The underground equivalent of this is the service pedestal (photo below). The service pedestal is a heavy plastic “forest green” colored column roughly 18” in diameter and buried a foot into the ground. With the protective cover attached on top, the pedestal stands about 24” tall. All cables come into the pedestal from below ground, and all the connections are made inside and kept out of view.

Because of their small size and weight, service pedestals do not have to be located close to streets or “improved” surfaces as padmount transformers do. Generally, a service pedestal needs to be located within 5 to 10 feet of the pole that has the overhead connections being undergrounded.    In many residential areas, the overhead wires are located in the rear of lots. When these wires are undergrounded, the service pedestal is placed in this area as well. Service pedestals are often located along property lines between adjacent lots.

With underground installations, there is usually a location where a physical transition is made from the overhead lines to the new underground cables. This transition is made on a terminal pole (photo at right). Notice the cable is connected to one of the overhead wires and heads down into a heavy gray plastic pipe or conduit. The conduit runs the length of the pole and straight into the ground.    Terminal poles are standard additions in most undergrounding projects and can be seen at or near the construction project boundaries.

8.

Q.

Why does AmerenUE install new underground systems in front lots? Why not place them in the back yard where many overhead poles are located?

A.

Accessing the rear of customers’ properties with large construction equipment is extremely difficult in mature, well-established yards. Swimming pools, detached garages, locked gates, dogs and landscaping are just some of the obstacles that can be encountered. Placing the new underground facilities in the front eliminates these issues and gives AmerenUE crews better truck access to equipment, which means less damage to private property and faster restoration times in the event of an outage. Installations in brand new developments all over Missouri are built this way for precisely these reasons.

9.

Q.

Why would some poles have to remain after an overhead line is placed underground?

A.

There are several reasons why poles may have to remain after the power lines on them are placed underground:

Some customers are paying for private area lighting that they want to retain for the benefits they provide, so those poles would have to stay.

Some customers with overhead service wires to their homes choose not to have those wires converted to underground even though AmerenUE is undergrounding its spans of wire from pole to pole. The individual poles that these overhead service wires are connected to would have to remain for those customers making this choice.

There are many poles in Missouri supporting not only electric lines but also telephone and cable TV lines. The tops of those poles that no longer carry our power lines are cut off so that they stand only as tall as needed for the other utilities. The maintenance of these pole “stubs” become the responsibility of these other companies.

AmerenUE has some equipment that must be located on poles because they have no underground “equivalent.” So there may be some poles that remain even after the wires are placed underground.

10.

Q.

What are some examples of instances where overhead- to-underground conversions would not end up being feasible?

A.

There are several reasons a overhead-to-underground conversion might not be feasible:

Private property owners are not willing to provide the easements necessary for AmerenUE to construct and operate the new underground system.

Locations exist where the necessary safety standards and operational requirements cannot be met, e.g. extremely congested areas where pad mounted transformers and switch cabinets cannot be installed with sufficient operating clearances.

The intended construction area is prone to flooding. Though this is not expected to be a problem in most areas of Missouri, excessive flooding can and does short out transformers, which then cannot be safely restored until the flood waters recede.

11.

Q.

What is involved in having the service wires to my house placed underground? What would I have to do myself?

A.

This photo (right) shows a typical overhead service entrance for a residential customer. Of the items shown, AmerenUE owns the service wires, house knob and meter—the customer owns everything else. In order for service wires like these to be placed underground, the customer is responsible for installing (1) a new meter box that accepts “bottom-fed” cables and (2) a new buried service conduit on the property to the underside of the new meter box. This is the plastic pipe that houses AmerenUE’s underground service cable. The customer is also responsible for removing the weather head, drip loop wires, service entrance pipe and old meter box. For those residential customers who choose to do so and perform the required work, AmerenUE will install new underground service cables to their homes and connect both ends free of charge.

12.

Q.

Can you be more specific about some of the costs in converting my individual overhead service wires to underground?

A.

The costs can vary widely and will depend on variables such as:

Whether your local electrical inspection authority requires your electrical installation or wiring to be upgraded as part of your conversion;

Whether an electrician (or other tradesperson) needs to dig and backfill an open trench or perform “directional boring” in order to install the conduit from the easement to the house;

The length of underground service line required for the conversion;

Whether or not your existing weather head extends through the roof of your house, in which case you would incur the cost of roof repair after the weather head is removed.