Fall of potential test voltageresistance rises dramatically. R is the earth electrode resistance reading in ohms. A is the spacing in metres between the test electrodes. If there is only one path to ground, the stakeless method will not provide an acceptable value and the fall of potential test method must be used. Ieee guide for measuring earth resistivity, ground impedance, and earth surface potentials of a grounding system. This is known as the fall of potential method and it can be seen in figure 3 below that most of the voltage is dropped around the electrodes where, as outlined above, the soil layers are. Ground impedance measurement methods the 2point method the 3point method the fall of potential method the 62% rule the ratio method the tag slope method the intersecting curve method staged fault tests driving point impedance the sgm method continuityintegrity testing soil resistivity measurements touch and step voltages. The 3point or fallofpotential method is used to measure the resistancetoground of existing grounding systems. The fall of potential grounding test is typically performed after the grounding protection system has been designed and implemented in order to tell you the grounding grid resistance value, which will indicate whether or not the ground has been installed correctly and whether or not it meets the national electric code standards. The measurement of earth resistance is made by the potential fall method.
In it, we have a current supplying electrode and a ground electrode, which essentially makes a circuit. Fall of potential ground testing clampon ground testing comparison recently, a ground resistance test was conducted tocompare the results obtained from the fall of potential 3point testingmethod to the clampon testing method. The fluke 1621 is an easytouse earth ground tester. Effective grounding provides a low resistance path for lightning and other phenomena that might otherwise damage electrical systems and injure personnel. Nov 20, 2015 fall of potential test voltageresistance rises dramatically i can not seem to make sense of this common drawing. The facilities under consideration must undergo periodic safety inspections.
Pdf analysis of a large grounding system and subsequent field. Ground resistance measurement with fallofpotential method. Nov 10, 2015 measuring resistance of ground electrodes 62% method the 62% method is an extension of the fall of potential method and has been adopted after graphical consideration and after actual test. May 16, 20 in this demonstration we show how to install your earth spikes and why they should be installed correctly. Det4 series 4terminal earthground resistance and soil. The ability to properly measure ground resistance is essential in preventing costly downtime due to service interruptions caused by poor grounds. Fallofpotential method electrical power generation. Fall of potential testing in an industrial plant good morning all, i wanted to get everyones experienceopinion on using a clamp on meter instead of the traditional fallofpotential test for ground testing.
Using a digital resistance meter we demonstrate the importance of depth and spacing of. The fall of potential method measurement process theory flat curve portion current return electrode current source voltmeter voltage probe apparent resistance ground under test true ground resistance distance from ground under test. Fall of potential test form page 1 of 3 project facility. The grounding systemconsisted of four copper clad rods installed in an approximate 20 ftsquare. Pdf on jan 1, 20, huan huang and others published analysis of a large grounding system and subsequent field. The earth ground tester works on the principle that in parallelmultigrounded systems, the net resistance of all ground paths will be extremely low compared to any single path the one under test. The goal in ground resistance is to achieve the lowest ground resistance value possible that makes sense economically and physically. This test requires a 3point ground resistance tester such as aemcs 4620 or 4630 ground resistance tester. Fallof potential ground testing and clampon ground testing. Unfortunately, the large resistance areas found in large ground systems may make it unfeasible or even impossible to carry out this test. This testing device was developed specifically for improving the speed and convenience of the ground test.
Field test validation using the fall of potential method. Grounding systems are critical components of electrical systems. Dead earth method or twopoint earth resistance test. Grounding is a critical component of electrical systems. Prospecting for good low resistance ground locations, or obtaining. Fallofpotential testing with the ground resistance. With reference to fall of potential, three points of contact are made with the soil. A common method for measuring the resistance of a grounding system is the fall ofpotential test, also known as the 3point or 3pole test. The fallofpotential test method is used to measure the ability of an earth ground system or an individual electrode to dissipate energy from a site. Bureau of standards now nist developed the theory behind this test in 1915 see reference pg. It may seem at first that each pylon is a single grounding point as each pylon is a standalone structure. The ground resistance tester model 3640 kit includes one 16 ft lead, two 150 ft leads on reels with windup handles, two 16 auxiliary ground electrodes, soft carrying case, batteries and user manual. The resistance area of the earth electrode is the area of the soil around which a voltage gradient is measured with a commercial instrument. The fall of potential method introduces two auxiliary electrodes, called return electrode and potential probe.
An alternative fallofpotential method is presented to measure online and in situ resistance of ground electrode systems in a lowvoltage distribution network. This paper examines various aspects of the design process and subsequent field test measurements of a large and complex substation grounding system. The first is the 3point or fallof potential method and the second is the induced frequency test or clampon method. The fallofpotential method or threeterminal method is the most common way to measure earth electrode system resistance, but it requires special procedures when used to measure large electrode systems. Second, the tester is connected to the earth electrode. The two primary requirements to successfully complete this test are the ability to isolate the grounding system from the utility neutral and knowledge of the diagonal length of the grounding system i. First, the earth electrode of interest must be disconnected from its connection to the site. This method is derived from the 4point method which is used for soil resistivity measurements the 3point method, called the fall of potential method, comprises the earth electrode to be measured and two other electrically independent test.
Fallof potential or threeterminal earth resistance test the resistance for this distance is 20. Guide for measuring earth resistivity, ground impedance, and earth surface. This is known as the fall of potential method and it can be seen in figure 3 below that most of the voltage is dropped around the electrodes where, as outlined above, the soil layers are small around the electrode and therefore holds the majority of resistance. Measurement of earth resistance the measurement of earth resistance is made by the potential fall method. The vector sum of resistance and reactance between a ground electrode, grid or system and remote earth. The most commonly used method of measuring the earth resistance of an earth electrode is the 3point measuring technique shown in figure 1. These factors emphasize the importance of a continuous, periodic program of earth resistance testing. How to perform a fall of potential test w aemc model 3640, 3. The fall of potential method depends upon a test current from a source to a single ground point, from which resistance can be calculated. This method applies only when all three electrodes are in a straight line and the ground is a single.
A common method for measuring the resistance of a grounding system is the fallofpotential test, also known as the 3point or 3pole test. Fallofpotential testing with the ground resistance tester model. The fall of potential test method is used to measure the ability of an earth ground system or an. The fall of potential test method is used to measure the ability of an earth ground system or an individual electrode to dissipate energy from a site. Figure 1 shows the measurement arrangement for this method of testing. Table 1 compares the estimated values of the grounding resistance computed according to 5, for the different. Ieee guide for measuring earth resistivity, ground impedance. There are some comparatively minor considerations in technique and procedure that apply to specific types of electrodes, but the similarities far outweigh the differences in testing across. The fall of potential method with current probe must be employed instead for testing ground resistance of lowvoltage pylons.
Measurement of earth resistance by potential fall method. Take measurements at voltage probe distance intervals of a maximum of 50 m for a distance of 300 m from the newpcc facility. Fall of potential testing in an industrial plant good morning all, i wanted to get everyones experienceopinion on using a clamp on meter instead of the traditional fall of potential test for ground testing. Fallof potential ground testing and clampon ground. A fall of potential test is the most general of methods for meeting the above criteria.
This paper presents a novel technique for measuring ground resistance of a grounding system with the fallofpotential method using capacitive probes. In situations where the stakeless method reading is questionable, a full fall of potential test is recommended. Methods of earth resistance testing part2 electrical. Measuring ground resistance with the 62% method ground resistance is a measurement of the conducting connection between a grounding system and earth. In many locations, the water table is gradually falling. Use the fallofpotential slope method for determining the resistance of large areas such as substation yards, ground perimeters of large buildings, and other large areas.
Fall of potential 0 10 20 30 40 50 60 0 20 40 60 80 100 distance between earth electrode and ref. Ground tests are named after the number of points that come in contact with the soil. In this situation with multiple paths to ground, the test current will flow to all four ground points at the building corners. The fall of potential test can be labor intensive and time consuming. The model 3620 features threeterminal operation for fallofpotential earth ground resistance and also may be used for 2point tests. To measure grounding accurately with this method, it is. Fallofpotential ground testing clampon ground testing comparison recently, a ground resistance test was conducted tocompare the results obtained from the fallofpotential 3point testingmethod to the clampon testing method. The procedure is specified in the ieee81 standard guide for measuring earth resistivity, ground impedance and earth surface potentials of a ground system. Checking ground electrode impedance for commercial. The first line of defense in detecting reliable ground connections, the unit features basic ground testing methods including 3pole fallofpotential as well as 2pole ground resistance. These factors emphasize the importance of a continuous, periodic program of earthresistance testing.
Pdf extended analysis of ground impedance measurement using. In situations where the stakeless method reading is questionable, a full fallofpotential test is recommended. Aemc fall of potential ground resistance testers from coleparmer. An overview of the ieee standard 81 fallofpotential grounding test. Principles and testing methods of earth ground resistance. How to perform a fall of potential test w aemc model 3640. Topics addressed include safety considerations, measuring earth resistivity, measuring the power system frequency resistance or impedance of the ground system to remote earth, measuring the transient or surge impedance of the ground system to remote earth, measuring. During the last decade, a new technology appeared in the market, in the form of the clampon ground tester. Ground resistance measurement with fallofpotential. Feb 21, 2020 i have read the dept of defense regulation that states that the 3point fall of potential test is the only acceptable method of determining ground resistance for the type of facility under consideration.
Aemc fall of potential ground resistance testers from cole. The 3point test requires complete isolation from the power utility. Addressing the testing challenges in large ground systems. Ground resistance measurement with alternative fallof. In a year or so, earth electrode systems that formerly were effective may end up in dry earth of high resistance. Fall of potential test voltageresistance rises dramatically i can not seem to make sense of this common drawing. The fallofpotential test method is used to measure the ability of an earth ground system or an individual electrode to dissipate energy from a. This method is generally not suited to large earthing installations, as the stake separations needed to ensure an accurate measurement can be excessive, requiring the use of very long test leads refer to table 1. When the return electrode is placed at a finitedistance from the grounding system and the potential probe is driven into the earth at a specific locationthe socalled. Measures soil resistivity 4point model ae211494 measures ground resistance 2 and 3 point fall of potential method. Ground resistance measurement, fall potential method youtube.
Use the fall of potential slope method for determining the resistance of large areas such as substation yards, ground perimeters of large buildings, and other large areas. Grounding techniques for tactical equipment and systems distribution restriction. It is the most accurate method but is limited by the fact that the ground tested is a single unit. Buy aemc fall of potential ground resistance testers and more from our comprehensive selection of resistance testers from coleparmer covid19 update. Recently, a ground resistance test was conducted to compare the results obtained from the fallofpotential 3point testing method to the clampon testing. This involves injecting a current into the ground at a distance from the grounding system under test, and then measuring potential at different points between the grounding system and injector electrode. The most common method of earth ground resistance measurement is the fall of potential method. X, yand z may be referred to as x, pand c in a 3point tester or c1, p2 and c2 in a 4point tester. T e s t i ng pr i nc i ple fall of potential 3point measurement the potential difference between rods x and yis measured by a voltmeter, and the current.
Ieee guide for measuring earth resistivity, ground. An overview of the ieee standard 81 fallofpotential. Utilizing a ground resistance meter digital is preferred, two auxiliary electrodes are driven into the soil at predetermined distances, per the testing specifications, in a straight line from the ground being tested. Earth resistance is measured in two ways for two important fields of use. The fall of potential method is often referred to as the three point method. An alternative fall ofpotential method is presented to measure online and in situ resistance of ground electrode systems in a lowvoltage distribution network. It may also be referred to colloquially as a threepoint test, although this term is also applied to a separate test that is likewise defined in ieee 81. A common method for measuring the resistance of a grounding system is the fall of potential test, also known as the 3point or 3pole test. Analysis of a large grounding system and subsequent field. In the ideal world, testing a large ground system would be conducted in complete accordance with the fallof potential method.
This paper presents a novel technique for measuring ground resistance of a grounding system with the fall of potential method using capacitive probes. The fallofpotential method is often referred to as the three point method. Fallofpotential test form page 1 of 3 project facility. Determining effectiveness of ground grids and connections that are used with electrical systems to protect personnel and equipment. This method should not be used as a standard procedure, but rather as a backup in tight areas. T e s t i ng pr i nc i ple fall of potential 3point measurement. Measuring earth resistance with fall of potential method photo credit.
The fallofpotential method introduces two auxiliary electrodes, called return electrode and potential probe. Pdf an extended analysis of ground impedance measurement using the fallof potential method is presented. An alternative fall of potential method is presented to measure online and in situ resistance of ground electrode systems in a lowvoltage distribution network. A practical guide to earth resistance testing weschler instruments. The most common methods of measuring the resistance of an. This test requires a 3point ground resistance tester such as aemcs 4620 or. Grounding techniques for tactical equipment and systems.
The study and measurements show that soil layering and lead interference can have a significant impact on the appropriate test location that yields the exact substation ground impedance. Measuring resistance of ground electrodes 62% method the 62% method is an extension of the fallofpotential method and has been adopted after graphical consideration and after actual test. The advantage of the det4tc2 and det4tcr2 is that the units include both test methods in a single instrument, making them the most versatile units available. Oct 12, 2016 how to perform a fall of potential test using the aemc model 3640, 3point ground resistance tester. Ground resistance depends on grounding electrode selection, soil resistivity, soil contact, and other factors. The threepoint method is the most thorough and reliable test method. The standard used as a reference for fall of potential testing is ieee standard 81. Commonly used terms refer to dead earth, fall of potential, and wenner method tests. The analog ground resistance tester model 3620 performs ground resistance measurements from 0. If there is only one path to ground, the stakeless method will not provide an acceptable value and the fall ofpotential test method must be used. In the dead earth method, contact is made at just two points. Application note april 17, 2002 on april 14, 2002, a ground resistance test was conducted to compare the results obtained from the fallofpotential 3point testing method to.
Its convenient size, rugged holster, and large, clear lcd display make it an ideal. A system of interconnected ground electrodes arranged in a pattern over a specified area and buried below the surface of the earth. The first line of defense in detecting reliable ground connections, the unit features basic ground testing methods including 3pole fall of potential as well as 2pole ground resistance. In this demonstration we show how to install your earth spikes and why they should be installed correctly. However, as in the building example in fig 2, there are multiple ground paths to take into account. Fallofpotential testing with the ground resistance tester. Application note april 17, 2002 on april 14, 2002, a ground resistance test was conducted to compare the results obtained from the fall of potential 3point testing method to the clampon testing method. Earth electrode measurement multiple probe system a second earthing resistance measuring technique is.
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