From the August, 2014 Issue of Cabling Installation & Maintenance Magazine
Newly patented technology makes it practical to field-test conduit plant.
By Erkan Gunal, Click2See
How many of us have ever needed a thoroughly validated conduit run prior to fishing a cable through? Envision the testing and certification process that we are doing for our copper and fiber plants. Wouldn't it be nice if we could have a certified conduit test report with colored graphs showing the length, diameter, number of junction boxes, bends, route, and so on, in addition to identifying inside obstacles, such as sharp edges, water, dirt, or even a collapse?
This article is meant to help us evaluate current field practices and the need for an industrial standard to validate our conduit infrastructure, and to introduce readers to technology that can address this issue.
The following nine methods, tools, and techniques are traditionally used to identify, track, and survey new and existing conduits in the field: A) electromagnetic underground object detectors; B) ultrasonic conduit detectors; C) electrical current-based tracers and detectors; D) use of a fish tape; E) use of a pulling string; F) use of a vacuum machine and air blower; G) shaking the existing cables or wires inside a conduit; H) shouting toward a conduit opening; I) knocking on a conduit with a hard object.
Following are brief descriptions of each technique.
Electromagnetic underground object detectors-In basic terms, a metal detector is used to locate hidden metallic objects. In technical definition, an electromagnetic inductive coil or directional antenna is positioned to detect metallic objects that are buried underground or behind a wall. These objects must be electrically conductive materials, such as metallic conduits, ducts, pipes, cables, and wires. However, this method is a challenge to detect a non-metallic object, such as an empty plastic duct or PVC conduit filled with a non-conductive optical fiber cable.
Ultrasonic conduit detectors-Ultrasonic sensors (also known as transceivers, when they both send and receive) work on a principle similar to radar or sonar, which evaluate attributes of a target by interpreting the echoes from radio or sound waves, respectively. Ultrasonic sensors generate high-frequency sound waves and evaluate the echo that is received back by the sensor. Sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to an object.
Electrical current-based tracers and detectors-This category includes handheld devices that are used by technicians to trace and identify metallic conduit runs.
Use of a fish tape-This is one of the commonly preferred practices by field technicians. A fish tape (also known as a draw wire or draw tape) is a tool used by electricians to route new wiring through walls and electrical conduit. Made of a narrow band of spring steel, by careful manipulation, the tape can be "fished" or guided through the confined spaces within wall cavities. Once guided through, the new wiring can be pulled into the wall by attaching it to the end of the fish tape and pulling the tape back from whence it came.
Fish tapes are usually stored coiled on a plastic reel. Because of this, they have a natural curvature, and this curvature allows them to be guided. By manipulating the reel, the end of the tape can be directed slightly. The tape is rigid enough that it can then be pushed in the direction in which it is pointing. In this way it can be easily guided through an empty wall cavity. Thermal insulation, firestopping, pipes, HVAC ducts, electrical conduits, and other obstructions make the use of a fish tape more challenging.
The "tape" can be made from many different materials including steel, fiberglass, and nylon. The tape usually has a special end, ranging from a hook or loop to a specialized fastener device, to allow the user to attach the tape to the cable before pulling.
Use of a pulling string-Pulling string (also known as a liner) is usually used to pull a wire or a cable bundle into a conduit. If an existing conduit already includes a pulling string installed, a technician can hold or observe the opposite end of the sting, while another technician pulls the string. If the string moves, then the correct conduit is identified.
Use of a vacuum machine and air blower-A vacuum machine is commonly used by field technicians to identify unknown conduit runs. At one end of the conduit, the inside air is vacuumed while the opposite end is verified by hand for suction effect. It is also practical to feed a pulling string or rope during this process. The opposite end of the pulling string should have a knot or a small object tied, to improve the movement and pulling speed inside the conduit. When the pulling string reaches the other end of the conduit, the identification is successfully completed.
An air blower is used to push the air inside a conduit toward the opposite end. Similarly, the blowing air is confirmed by hand at the other end.
Shaking the existing cables or wires inside a conduit-Shaking the existing cables or wires inside a conduit is another common practice in the field to identify unknown conduit routes. One technician shakes the cables inside the conduit run, while another technician observes any movement at the opposite end.
Shouting toward a conduit opening-If there are no handy tools accessible in the field to identify an unknown conduit run, a technician may shout into a conduit opening or a pull box, while another technician listens to the incoming sound at the opposite end to confirm the direction of the route being tested. Acoustic sound waves can travel significantly long distances when guided.
Knocking on a conduit with a hard object-Another common field technique is knocking on a conduit repeatedly with a hard object, such as a hammer, screwdriver, etc., while another technician listens to the knocking sound to confirm the correct conduit run.
Problems and solutions
To gain wider insight into the types of conduit-identification challenges being faced in the field, I started a discussion topic on a social media site. That discussion produced the following feedback.
• This kind of solution is definitely needed for infrastructure projects like airports. We are doing the visual inspection after every conduit installation, which is not that efficient [or] accurate."
• Conduit runs in the data center are rarely documented properly."
• Working inside large conduit banks for individual identification of pathways and possible detection of collapsed or blocked conduits are not easy tasks."
• There is absolutely a need for immediate identification of which conduit to use. With [an effective] solution ... no more questions as to which conduit terminates in which location."
• Tracing conduit has always been a hassle. I need a real time-saver for my site walks."
A patented product does exist to meet the challenges described above. "Conduit Toner and Detector" (CTD-U.S. Patent No. 8,220,332) was inspired by a standard inductive amplifier and detector, also known as a cable toner. However, instead of using electrical conductivity, the CTD uses acoustical sound vibrations to analyze the conduit under test. Sound vibrations can travel miles away when they are guided. A sound generator and detector are used to validate any point-to-point route of conduits inside building walls, floors, or underground maintenance holes at the speed of sound. The sound frequency can be adjustable depending on the application or test being performed.
Tracing a concealed conduit or underground duct bank can be done safely and efficiently with or without existing cables inside, regardless of conductor type, gauge or energized/non-energized condition. The CTD has the ability to test a conduit regardless of its material type (conductive or non-conductive). Therefore, the conduit's material (metallic or non-metallic, such as EMT or PVC) does not affect the tester's operation.
Consider the use of this type of instrument in the everyday operations of outside-plant (OSP) installations and surveys. On these jobsites, it often occurs that a field inspector or owner is curious about the condition of an installed conduit plant. Or a cabling contractor, working with conduits that were installed by others, may need to determine the intended route and path of a given conduit dedicated to their own scope of work. And an estimator may wonder what the physical relations of an existing conduit infrastructure are, in order to determine the correct cable path and length.
A recent survey we conducted among nationwide electrical and low-voltage contractors (illustrated in the pie graph) showed that 15 percent of their field technicians shout or blow into a conduit in order to validate the correct route. Twenty-three percent shake the wires; twenty-five percent prefer to use a vacuum cleaner and pulling string; thirty-five percent use a fishtape, and two percent have other preferred techniques to determine the destination and condition of a conduit run.
The CTD can improve current field-safety standards and practices when compared to conventional techniques. For example, the use of a steel fish tape to identify a conduit route can be highly dangerous while fishing through energized cables. Potential damage to fiber-optic or low-voltage signaling cables may occur if the cables are disturbed by any mechanical means, such as using a fish tape or other device causing physical impact.
One of the companies I have worked with in the past had a recordable injury incident. One of our electricians wanted to identify a low-voltage conduit using a steel fish tape. Apparently there were unidentified existing cable bundles inside the conduit. When the electrician started fishing through the conduit, he realized it was energized and he was shocked by 480 volts. The CTD is an ideal instrument for these types of unsafe conditions. Sounds waves can travel along with existing cables throughout the conduit, up to 40- to 60-percent fill ratio. The CTD does not require a direct contact with conduit openings.
Getting schooled
Another OSP project with which I was involved included a deep survey of an existing underground duct-bank system with approximately 40 maintenance holes. The campus did not maintain any as-built plans for their communications systems. They were planning to add multiple new buildings and wanted to know how to tie into their existing infrastructure. Our task was to identify and document all the relations between the communications duct banks, and also tag existing cables with waterproof labels for accurate system identification.
I had a field crew on board, and they were opening the maintenance-hole covers one-by-one, having to go inside to take pictures and draw sketches for each duct-bank direction. They identified each cable by their count, type, color, make and diameter, so they were able to track them from one end to the other. From time to time they needed to shake the cables in order to identify the correct cable jacket at the far end.
On day one we were able to complete our scheduled tasks successfully while gathering a great deal of valuable information. However, the next day my company received a phone call from the plant facilities office; they were concerned about a faulty notification on a fire-alarm annunciator. Apparently there was a communication fault at one of their existing fiber-optic nodes between fire-alarm control panels. The facilities were blaming my crew for being inside the maintenance holes (we were the last ones there) and disturbing the splice boxes that were part of the fire-alarm system. I was told we needed to troubleshoot their fire-alarm system and provide a fire watch until the system was restored.
I demobilized my crew from the field immediately and hired a fire-alarm company to locate and fix the problem. Meanwhile, we received other complaints from the school's administration office that the faculty had lost network connectivity, printers were not working, and other similar concerns. Obviously, my company became the proverbial sitting duck and was being blamed for any critical technical issues throughout the campus.
During the troubleshooting, it occurred to me that using acoustical sound vibrations could identify conduit duct-bank relations without disturbing any cables. I developed a prototype and shared it with the plant facilities office, which liked the concept primarily because we did not need to touch any cables. A few days later, the fire-alarm company we hired was able to fix the problem (a bad network port inside one of their fire-alarm control panels). Additionally, the connectivity issues among faculty members were "magically" resolved by their internal information-technology department.
Finally, we got the OK to return and continue the survey. We identified all the maintenance holes with GPS coordinates, laid out physical duct-bank relations, and tagged all existing cables per system. The task was completed three months earlier than initially planned. Our client was satisfied that we took ownership of the situation and provided our assistance, as well as creative solutions, to complete the contract on time and under budget. Consequently, we were awarded additional projects on the campus.
The benefits of conduit testing and validation are numerous, and could be geared toward improving current standards to which we adhere. The coverage of the patent mentioned in this article also could be applied to plumbing and piping industries. I believe this technology will open an important gateway toward new industrial standards while making it possible to field test and document new and existing infrastructure on large scales. I'm proud to have invented this technology that may usher in a new era.
Erkan Gunal, BSEE, RCDD, NTS, NICET, FA-III, STS is president of Click2See (www.click2see.us). He holds three patents, including U.S. Patent No. 8,220,332.