Preparing for Winter Underground Work
Published in: Transmission & Distribution World,
Date: 12/1/2004
By: Susan Soles and John Ryan
As utilities prepare for winter, one thing is certain: Underground work can be wet and messy. NYSEG URD crews often are faced with new extension projects that come in the winter when the ground is notorious for freezing and then thawing. A new line extension to a residential development or commercial site is a typical project for the utility, which serves more than 840,000 electricity customers and 250,000 natural gas customers in the Northeast. These jobs cannot be postponed until the weather improves.
Joint-Trench
Joint-trench, sometimes called “common trench” installation, is becoming more prevalent. Some utilities are apprehensive about the close proximity, especially when emergency repair and maintenance is necessary. Others have encountered bottlenecks with the logistics of trying to coordinate multiple engineering departments. However, in recent years, a growing number of utilities – including NYSEG (Binghamton, New York) – are realizing the benefits of joint trench, which include:
*Fewer construction crews working in the area improves worker safety and lowers the risk of hitting other utility.
*Shared cost between jointly installing utilities saves participating utilities 30% to 40%.
*The timeline from design to completion is shortened when a standard multi-utility installation design is used.
*Builders, developers and the community appreciate the conservation of right-of-way.
*The uniform design makes it easier for future excavators to locate existing utilities.
*Using spacers for gas-electric installations eliminates the danger of lines crossing and damaging other utilities’ lines in the right-of-way.
Cheaper Than a Box of Dirt
This last point, “separation,” is especially difficult in the winter in NYSEG service area. Snow often covers the area for weeks, and the ground melts and freezes again and again. All of this creates a muddy, messy place to try to keep a ditch open during gas and electric installations. Until a few years ago, NYSEG underground crews used 6-inch by 12-inch cardboard boxes filled with dirt to separate utilities in a common trench. Boxes were placed between the gas and electric lines, and filled with dirt for stability until the trench was backfilled. In wet, raining conditions, the boxes collapsed and the fill dirt became like soup. It was a mess and the real kicker was the loss of the boxes at $12 apiece.
In 2001, the box-of-dirt separation procedure was re-evaluated. It was decided to switch to a more consistent and cost-effective method – Common Trench Spacers. This simple snap-on separator was developed by Innovative Trench Solutions Inc. (Webster, New York), which was formed by two NYSEG employees, John Ryan and Julius Martin.
Putting It to the Test
This past winter, on two joint-trench projects, the spacers were used to maintain separation of gas and electric lines in a common trench applications. In Walden, New York, a new line extension project for a new Bruderhof Communities plant called for the installation of gas, electric, telephone and CATV in the same 1300-foot trench. The spacers were used to install NYSEG’s gas and electric lines. The manufacturer worked closely with NYSEG crews who have developed a spacer placement procedure for successful multiple-utility installation:
* Placement of utilities
Field crews recommend installing the other wire utilities, telephone and CATV first in the 2.5- to 3-ft wide trench. NYSEG crews then roll out the electric cable along one side of trench. Next, the gas service line is rolled out on the opposite wall of the trench.
* Install tracer wire
After all of the utilities are in the trench, crews lay out the locater tracer wire. The wire is secured in place by staking it at one end of the trench and keeping it tight as it is rolled out along the center of the ditch between the electric line and gas pipe. At the far end of the ditch, the tracer wire also is tied off to keep it tight until it is backfilled.
* Attach spacers to gas and electric lines
The 12-inch spacers are designed to easily snap onto the gas, electric and tracer wire in the trench. The spacer is first connected to the gas line positioned perpendicular to the other utilities in the trench. Spacers are attached at 10- to 15-ft intervals along the pipe or more often where the trench curves. As the spacers are snapped on to the gas line, they are tucked under the other wire utilities and tracer wire.
* Attach tracer wire
Crews then attach the tracer wire at the center clip of the spacer, 6 inches from the gas line, gently tugging at the tracer wire to take out the slack and maintain a taunt position. This procedure is to comply with the new federal regulations on minimizing contact of tracer wire and plastic gas pipe (49 CFR Part 192.321). To complete the separation process, crews place the opposite end of the 12-inch spacer underneath the line to ensure 12 inches of separation.
* Inspect and record
Before backfilling the trench, a final inspection of the trench is conducted. It is recommend that crews note on the drawings which side of the tracer wire the gas and electric lines are placed. This makes it easier for future line locating and excavating in the area.
* Backfill
A key benefits of the spacers is the confidence of knowing that once the sanding and/or backfilling is complete, the utilities are still separated as required by company and industry guidelines, and the tracer wire also is in place to give accurate locations of the buried lines.
In another joint-trench project in Goshen, New York, safe separation procedures were followed using the Common Trench Spacers. The winter job called for extending new service to The Hills of Goshen subdivision. NYSEG crews installed the gas line in conjunction with Orange & Rockland Utilities Inc. (Pearl River, New York), the electric company serving the area. Frontier Telephone and Time Warner Cable also placed their cable in the trench. Melting snow again made for a muddy ditch for the entire 3700-ft extension. Spacers were determined to be the only way to keep the lines separate.
We would have had a heck of a time without the spacers.
Separation Compliance
These projects highlight the aggressive measures NYSEG is taking to adopt safe separation guidelines that recently have been approved for the underground utility industry. In 1999, a gas explosion in Virginia involving arching electric lines near gas lines was the cause of a fatality. The National Transportation Safety Board (NTSB) investigation concluded, “Had the gas and electrical service lines involved in this accident been adequately separated, the heat from the arcing electrical failure would probably not have damaged the gas service line, and the accident would not have occurred.”
The report went on to say that the presence of corrosion and subsequent overheating and arcing at a splice in one of the conductors of the nearby triplex electrical service ignited an overlapped gas line, causing the explosion that resulted in the fatality.
For many years, NYSEG has followed the National Electric Safety Code, Rule 352A, separation guidelines, which states, “The horizontal separation between direct-buried cable and other underground structures should not be less than 12 inches.”
After the Virginia fatality, the NTSB asked a Common Ground Alliance (CGA) subcommittee to write a separation best practice. It took the subcommittee 18 months to gain industry-wide consensus on the separation guideline. In September 2003, the CGA board of directors approved for inclusion in the CGA Best Practices Manual the following best practice for separation:
“When installing new direct-buried supply facilities in a common trench, a minimum of 12-inch radial separation should be maintained between supply facilities such as steam lines, plastic gas lines, other fuel lines and direct-buried electrical supply lines. If 12 inches of separation cannot be feasibly attained at the time of installation, then mitigating measures should be taken to protect lines against damage that might result from proximity to other structures. Examples may include the use of insulators, casing, shields or spacers. If there is a conflict among any of the applicable regulations or standards regarding minimum separation, the most stringent should be applied.”
Detroit Edison’s Al Yonkman, who represents the electric utility industry on the CGA board of directors, says, “It was a highly debated issue because of the impacts on all utility installation procedures, but it will establish a safer standard for installation of utilities, save lives and help prevent utility damages in the future.”
Conclusion
For several years, NYSEG has been using spacers in joint-trench installation to comply with permanent safe separation guidelines. The company has found that spacers are a simple way to keep utilities and tracer wire separated in joint-trench applications. In addition, spacers have solved the problems associated with installing cable and pipe in muddy conditions. They also are economical, costing only about $2 per spacer, which is considerably less expensive than the $12 cardboard boxes used by crews a few years ago.
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