Moving in the right direction

April 2010 » Web Exclusive
Gradual underground conversion increases city's electric grid security and reliability, decreases maintenance costs, and improves aesthetics.
Installing new power lines underground requires only a small, hand-dug hole. HDPE pipe is pulled through the soil using horizontal directional drilling.

Staying true to its motto — “Where tradition meets progress” — Princeton, Ill., a city of about 7,500 residents located 115 miles west of Chicago, continues to modernize itself through a program is which all overhead electrical utility cables eventually will be put underground. From the beginning of the program seven years ago until late in 2009 when cold weather conditions pre-empted additional work, miles of underground lines have been installed. The primary goal is safety. Going underground by using high-density polyethylene (HDPE) conduit pipe eliminates the need for crews to climb and trim tree branches that grow around the power lines. And there are other benefits for the picturesque and historical city.

Project
Underground wiring, Princeton , Ill.

Participants
Princeton Electrical Department
Blue Diamond, LLC

Product application
Small city uses horizontal directional drilling and HDPE conduit to move overhead utilities underground.

“While some large and very abundant cities fear putting utilities underground because of unfounded opinions about cost, Princeton has embraced the idea,” said Tony Radoszewski, executive director of the Plastics Pipe Institute (PPI). “ Princeton is a small city with sharp-thinking leaders, namely its civic officials and its electrical utility managers. They know that by burying power lines and at the same time planning for the expanding use of technology, Princeton will have a confident power grid for many generations.”

Princeton 's utility-conversion program is being done in small steps. “We try to do at least one project every year where we convert from existing overheads that end in an easement in a backyard,” said Jeff Mangrich, superintendent for the city of Princeton Electric Department.

The installation directionally drills the HDPE conduit in the ground. This method requires little disruption of the surface, saving money and time that would be required to repair a large trench used to install pipe made from other materials.

“The reason we selected HDPE pipe is because we bore everything in,” Mangrich said. “We prefer not to do any open trenching because boring is so much less invasive. For some new developments and new construction sites, however, we choose between boring or cut and cover depending on whether or not we have a boring machine available. It's also easy to fuse HDPE pipe in the trench.”

For Mangrich and his crew, the job is also easier and quicker because the pipe comes in coils so hundreds of feet can be installed without stopping, greatly increasing productivity. The length of the coil depends on the size of the pipe. For example, as much as 6,000 feet of 2-inch-diameter HDPE pipe can be delivered on one reel.

The city of Princeton , Ill. , installs three HDPE conduit pipelines at the same time for electrical service and for future fiber optic cables.

“The HDPE pipe also enables us to use one pull to put in three different sizes — 1 inch, 2 inch, and a 2-1/2 inch,” Mangrich explained. “The 2 inch is used for primary conductor; the 2-1/2 is used for secondary conductor; and the 1 inch is for future fiber and is empty. This is all done in the same bore. We use a 6- or 8-inch back reamer and pull them all at the same time. This year we also installed some 4-inch-diameter conduit. Basically what we're doing is using the HDPE conduit to cut its own the pathway in the soil.” The electrical cable is then pulled through the conduit.

Blue Diamond, LLC, a PPI member company, manufactures the HDPE conduit pipe used for Princeton 's modernization. The conduit pipe has pre-installed pull tape, which makes it easy for Mangrich's crew to run the power cables.

The conduit is RUS/USDA listed and meets all ASTM specs for SDR, SIDR and NEMA-rated duct. It is also listed to UL 651 for the protection of cable and wires. The pipe's high tensile strength-to-weight ratio, superior crush resistance, and low coefficient of friction for cable installation makes it preferable for directional boring.

The main power line is generally run under the backyard of a house. The service line is run underground to the house with the homeowner paying an electrician to make the connection.

Safety, security, and aesthetics
Aside from providing the citizens of Princeton with a state-of-the-art utility system, Mayor Keith Cain knows the disappearing power lines reduce eye-pollution. “Our [citizens] love the idea,” he said. “As we continue to bury underground services, they get even happier because they like the improvement in how their community looks. We all want Princeton to look clean, and carefree. No one wants the poles and the wires sticking up through the trees throughout our community.”

Cain, who started the overhead-to-underground conversion during his early years as mayor, also realizes the other benefits. “Because we're eliminating the overhead lines, we don't have near the maintenance or the downtime due to ice storms, strong winds, or other severe weather events,” he said. “So as we gradually proceed on this project, I see a lot of cost effectiveness. There is an upfront cost, but in the long run it will end up paying for itself and will give better service to our customers. We're looking for zero outages. That's important to residents and critical for our businesses.

"By going underground and using HDPE pipe, it's definitely improving the quality of life,” Cain said. “We also use HDPE pipe in storm sewers and for potable water service lines for many of the same reasons.”

“Putting utility wires underground is a practical and necessary thing to do,” said Radoszewski. “It eliminates interrupted service due to weather or accidents such as a car hitting a pole. Plus it protects workers and citizens. HDPE conduit helps to preserve and protect a community. And on the green side, it saves the community's beautiful trees and eliminates the need to cut down others to make the many wooden poles that rot and crack and fall across the roads. Electrical co-ops in the United States purchase nearly 800,000 wooden poles each year. There are also many favorable environmental aspects of pipe made from HDPE including how it can build a long-life system. It is truly a sustainable and environmentally responsible choice for the nation's infrastructure.”

This article was contributed by the Plastics Pipe Institute, Inc. (PPI), a Texas-based, non-profit trade association that represents all segments of the plastic piping industry. More information is available online at http://www.plasticspipe.org.


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