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How to Find Power Lines Under Ground

written by: Om Thoke • edited by: Lamar Stonecypher • updated: 7/31/2010

If you are planning to carry out a landscaping or construction project involving digging up the yard, then the first thing you have to do is to locate the underground power lines, gas lines or other cables in order to avoid damage to the lines. So, here's how you can locate underground power lines.

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    Overview

    The damage caused by digging lines may result in service interruption or may cause severe injuries. Locating these lines is hence very safe so that these problems can be overcome. So, you must be wondering as to what the best way of locating underground power lines really is.

    Many local utilities can help you in finding the buried power lines. They make use of special devices to find out the underground lines. You might have come across people surveying the ground with wand-like or metal locating devices. Have you ever wondered what these people are up to? They try to detect the underground cables with the help of these wand-like detectors. Once these lines are detected, they spray paint on the surface of ground or plant flags of different colors to indicate different lines; normally a red color is used to point out power lines.

    Now, the digging work can be started by being careful around the colored lines. But, how do these devices detect the buried lines?

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    How Do Underground Power Line Detectors Work?

    The basic principle on which, the underground power line locators work is very simple. A cable that has AC power passing through it generates signals of its own in the frequency level of 50 to 60 hertz, jointly with greater frequency signals; this concept provides a foundation for finding the buried lines with the help of a passive receiver.

    The earth is filled with power frequencies circulating between the earth connection spots and cables. These currents follow the path of the underground metallic conductors automatically providing minimum resistance. They are also united with them by making use of induction and capacitance. Thus, a range of 50-60 Hz waves and their harmonics up to around 3 KHz are there on the underground cables as well as on the surface of most conductors in the vicinity. This means that lines that carry power frequency waves can be located, but they cannot be identified by inactive signal location. The signals may be from a live wire, concrete reinforcing bars or a pipe, but the presence of a conductor is confirmed.

    Single phase cables normally radiate clear waves, but with the case of three phase power cables, there is difference between the phase loads; this unbalance is due to the tendency of balanced currents to cancel their fields. As the balance improves, it becomes more difficult to detect the power lines. High voltage loadings like the ones for street lighting are better balanced; these can be easily detected by utilizing the option of passive search in ‘P’ (power) mode.

    However, sometimes live unloaded cables may be present; such cables do not radiate any power signals. To detect such cables, there is a radio mode option on the detectors which adds up as a great complement to the power mode. The radio frequency signals in this mode helps in detecting the existence of a conductor. Hence, detectors can be used in radio mode for detecting dead power cables which may go undetected in the power mode.

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    Detecting the Other Cables Running Underground

    Power lines are not the only cables that run under the ground. There are many other buried cables like the ones for gas lines, water lines, telephone and cable TV lines. Making use of single frequency detectors or multiple frequency locators, any of these lines can be detected. There are also separate locators available for each of these requirements.

    Different detection techniques must be used for different types of buried lines. For instance, detection of metal cables and pipes can be done using electro-magnetic devices while radio-location devices are used for detecting non-ferrous plastic or concrete lines.

    Detecting the underground is becoming more intricate with the increasing traffic of the buried cables. But still, it is very important to identify these lines to ensure safety of the diggers as well as to avoid damage to the lines. There are many companies that offer efficient line detectors to make the work easier. Some of the manufacturers include Schonstedt, C&S Solutions, Metrotech, etc. The equipments from Schonstedt are the most popular in the market of underground utility detectors.

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    In a Nutshell

    Most of these locators are versatile in finding different utility lines. The devices are designed to withstand the harshness of field handling under different climate conditions. Underground power line detectors are thus very efficient and quick in identifying the buried lines easily without digging, drilling or probing.

    You may also want to read more on GPS Surveying Systems.