Successfully locating and identifying buried utilities is a process of elimination – elimination of mistakes. A thorough understanding of the jobsite and the equipment’s correct operating procedures can help you efficiently mark a dig site for safe excavation. No matter what locating equipment you are using, following these guidelines will help you communicate to drilling or excavating crews precisely where they can dig safely.
Jobsite awareness is critical. You should gain as much knowledge about the location of the facilities as you can before pulling out your pipe and cable locator.
Review the locate request. Carefully review the dig ticket to ensure you understand the scope of the ticket and locate the entire area covered by the request.
Make use of available facility records. Facility records indicate approximate location, number of facilities, and access points for buried facilities within the jobsite area. If there is any doubt about the accuracy of the facility records, verify their location with a physical locate. Mark the locations to ensure they are not damaged during excavation.
Visually inspect the jobsite. Visual inspection assists you in determining if there are additional facilities not on record. Evidence of a facility includes poles, dips enclosures, pedestals, valves, meters, risers, and manholes. If you notice any of these features, be sure to locate and mark all utilities associated with them.
Know the Process. Pipe and cable locators locate the electromagnetic (EM) field produced by the AC current flowing on the line, not the pipe or cable itself. Many non-metallic pipes and cables have tracer wires buried next to them that can conduct electricity.
EM pipe- and cable-locator equipment systems consist of a transmitter and a receiver that are portable and, when properly used, very accurate. After identifying the best access point to the target line, the operator can place a signal on the line either by direct connection, clamp induction, or broadcast induction. The most accurate method is direct connection, which involves the signal traveling from the transmitter, through the target line, and returning through the ground stake. Only operators qualified to work with electricity should connect to an electric line.
Recommended procedures for direct connection:
• Remove any common connections to other utility lines to prevent the signal from being placed on untargeted lines.
• Insert the ground stake to the left or right of the target line’s suspected path. The transmitter’s black ground wire should not cross other lines.
• Connect the black transmitter wire to the stake and the red transmitter wire to the target line. Remove paint, dirt, or corrosion from the target line.
2.Power and Frequency Selection
• Select transmitter settings to match the conditions of the locate. Begin with minimum power level and low frequency and increase as necessary. The higher the frequency, the more likely your signal will bleed over to adjacent lines, and the shorter the distance your signal will travel.
• Set the receiver frequency to match the transmitter frequency. Conduct a 360-degree sweep around the access point where the transmitter is connected to the target line. A strong signal response will help determine the direction of the target line.
4.Tracing the Target Line
• One the direction of the target line is determined, sweep the receiver perpendicular to the target line and walk its path. Retrace the path and mark with the proper color paint or flags.
The receiver/transmitter system is accurate when used properly, but distortion and ground conditions can affect the signal. The only way to verify exact depth and location of a target line is to expose it. Most state dig laws have a defined tolerance zone in which only hand or soft excavation tools, like vacuum excavators, can be used to safely expose the target line.
These locating procedures are general guidelines and are not intended to be a comprehensive guide to operating your electronic locating system. Your operator’s manual contains complete recommendations and instructions for correct operation and maintenance.
Christopher Thompson is Utility Locator Product Manager with Subsite® Electronics. Learn more about Subsite’s comprehensive suite of electronic products at subsite.com.