Back to Reliability

What is Undergrounding?

“Undergrounding” is removing overhead power lines and equipment and burying them underground. As part of Ameren Missouri’s continued commitment to make our system safer and more dependable, we sometimes bury power lines and equipment that are particularly susceptible to outages, especially during storms or in heavily wooded areas. 

All of the equipment and hardware on Ameren Missouri’s overhead power lines is typically attached to a wooden utility pole and visible to the eye. While most of this is buried when undergrounding, some equipment must remain above ground in order for workers to access critical components. 
To learn more about installing power lines underground, call 800.552.7583. Customers can choose to have the service lines to a home or building placed underground. Learn more about this option.


Power Lines

The picture to the left shows what customers see in their communities, overhead wires with anywhere from two to six wires in the span. The higher voltage power lines are at the top of the utility pole, with the low-voltage wires positioned just below. Overhead power lines represent some of the greatest threats to service reliability because of their susceptibility to storm and tree damage.

The underground equivalent of overhead wires is underground cable in plastic piping buried in the ground. As a result, these cables will not be seen after they’re buried.


A transformer is a piece of equipment that changes, or transforms, high-voltage electricity to lower voltages for use in homes and buildings. An overhead transformer is a gray cylinder-shaped metal tank fastened to a utility pole and connected to several overhead wires. The overhead transformers will be removed along with the spans of wire from pole to pole during an undergrounding project. 

The underground equivalent of the overhead transformer is the padmount transformer -a forest green metal box on a small concrete pad found in green spaces such as yards (pictured at the top of the page). In residential areas, the transformer’s dimensions are roughly 32” tall x 34” wide x 34” deep. All cables enter from below ground and all connections are secured inside the transformer box. 

Padmount transformers must be located close enough to streets, parking lots or finished surfaces to allow crews to install and remove equipment using large trucks. In residential areas, transformers are typically in the front of properties, roughly 15 to 20 feet from the street along the property lines between adjacent lots. 

Connections - Overhead

In a new underground installation there is usually a point somewhere in the nearby power lines where the transition is made from overhead wires to the new underground cables that will connect to the padmount transformer. This transition from overhead to underground is made on the terminal pole. In the picture, the cable is connected to one of the overhead wires and heads down into a heavy gray plastic pipe, or conduit, which runs the length of the pole and straight into the ground. 

There are numerous locations on poles where Ameren Missouri’s spans of wire are connected together. These connections are necessary to distribute the low-voltage lines from a single overhead transformer to each home or business it serves. In an undergrounding project, these connections will be removed from the pole. 

Connections - Underground

The underground equivalent of an overhead connection is the service pedestal. It is a forest green plastic column roughly 18” in diameter that is partially buried in the ground. With its protective cover attached on top, the pedestal stands about 18” tall. All cables come into the pedestal from below ground, and all connections are out of view. Because of their small size and weight, service pedestals do not have to be positioned close to streets or hard surfaces like padmount transformers. Generally, service pedestals need to be located within five to 10 feet of the pole that has the overhead connections being undergrounded. In many residential areas, the overhead wires are in the rear of lots. This means the service pedestals would be located in the back of the lot as well, usually along property lines between adjacent lots. 
Alert Info