Well Organized and Uniform Trenches
Can Prevent Costly Accidents
The way in which utilities choose to install their underground facilities today will determine the integrity of those facilities for years to come.
Because more and more companies are utilizing underground space for their distribution systems, trenches are being dug to house pipe, conduit and cable and common trenching has become a popular, cost effective method for installing multiple utilities. Efforts to protect the safety of the public and prevent third party damage to these facilities include above ground markings, accurate mapping, use of sophisticated locating instruments and safe digging practices. While all of these steps are important, safety and damage prevention begins at the time utilities are installed in the ground with good trench “housekeeping.” This means taking the time to ensure proper separation of utilities in a common trench and maintaining proper separation of the tracer wire when installing plastic pipe.
Innovative Trench Solutions, Inc. of Rochester, New York has developed two new products to help achieve safer and more uniform underground installations.
The Tracer Spacer: Invented by an employee of NYSEG (New York State Electric & Gas), the Tracer Spacer is a simple, snap-on device designed to provide a consistent separation between plastic pipe and its tracer wire.
Tracer wire is an important component in a plastic piping system, aiding in the location of the pipe in the future. Proper spacing between the plastic pipe and the tracer wire has become a safety concern. If there is too much separation, future locates could be grossly inaccurate, possibly resulting in costly dig-ins. If there is no separation between the tracer wire and the pipe and the wire should become accidentally energized by a lightning strike or a crossed electric line, it could melt through the pipe and create a leak. This could result in the loss of life or property, and costly repairs.
The Tracer Spacer serves the dual purpose of holding the tracer wire far enough away from the pipe as to not allow contact, yet close enough to increase the accuracy of future locates. This is important because most states now require an accuracy of +/- 18 inches when marking out underground facilities.
NYSEG installed several hundred Tracer Spacers on 2” mains and ½” services during the summer of 2001. They wanted to determine if they were practical to use and if they maintained a more consistent separation than what could be achieved by simply laying the tracer wire along side the pipe. They were gracious enough to share some of their test results with us for use in this publication.
One NYSEG test site was in Vestal, NY where 810 feet of 2” medium density polyethylene gas pipe was installed along the side of a new shopping center. Beginning in the northeast corner of the building and continuing for 165 feet, Tracer Spacers were installed every eight feet. The installation of the Tracer Spacers was observed to assess ease of use, speed and practicality. This was the test section.
As the pipe, tracer wire and Tracer Spacers were backfilled with sand padding, the separation of the pipe and tracer wire was measured every four feet. These measurements were recorded to determine the effectiveness of the Tracer Spacers at maintaining a uniform separation despite the potential movement caused by backfilling.
For the next 140 feet of pipe, no Tracer Spacers were used. The tracer wire was laid in by hand next to the pipe and sand padding was installed. This was the control section. The separation between the pipe and wire was again measured and recorded every four feet. The results were as follows:
The Tracer Spacer is designed to hold the tracer wire 5” from the pipe. In the test section, 92% (37 of 40) of the measured separations between the tracer wire and the pipe were between 4” and 6”. Minimum recorded separation was 4” and the maximum recorded separation was 8” (in one instance).
In the control section, less than 7% (2 of 31) of the measured separations between the tracer wire and the pipe were between 4” and 6”. Minimum recorded separation was 0” and maximum recorded separation was 9”.
Workers installing the Tracer Spacers reported that they required no additional installation time and felt that they were easy to use and produced a more professional result than their traditional method of installation. In this case, use of the Tracer Spacer cost less than seven cents per foot of pipe installed. Based upon these results, NYSEG is proceeding with the approval process for adopting the use of the Tracer Spacer as a standard operating procedure.
Additional benefits of the Tracer Spacer include the ability to install it in all soil conditions and elimination of the time consuming chore of padding the wire and then padding the pipe, greatly increasing jobsite productivity. Looking towards the future, installing the tracer wire parallel to the pipe also ensures an accurate depth location which cannot be achieved when the tracer wire is installed either above or below the pipe.
The Tracer Spacer for Common Trench: Like the Tracer Spacer, this simple device will hold the tracer wire in close proximity to the plastic pipe while additionally ensuring that the other utilities in a common trench maintain at least a 12” separation and do not become displaced during backfill.
For the safety of the public and the integrity of the installation, it is important to ensure that plastic pipe does not make contact or even come in close proximity to any underground electric cables in a common trench installation. The National Electric Safety Code calls for a minimum of 12” of separation between direct buried cable and other underground structures such as fuel and water lines.
Most of our customers have been searching for an economical way to organize and standardize their common trench installations without slowing down production. Use of the Tracer Spacer for Common Trench ensures consistent results no matter how many different crews are involved in the installation process. These consistent results will also make future locates easier and more accurate.
Tracer Spacers for common trench applications can be used in virtually any conditions including wet trenches and rocky installations. The snap-on design greatly increases jobsite productivity in comparison to other methods of separation.
