The vector sum of resistance and reactance between a ground electrode, grid or system and remote earth. Ideally, to maintain a reference potential for instrument safety, protect. Ground testing in electrical maintenance the what, why. The resistance area of the earth electrode is the area of the soil around which a voltage gradient is measured with a commercial instrument. This makes the fall of potential test more useful prior to a facility becoming operational or when it is shut down for maintenance. A common method for measuring the resistance of a grounding system is the fallofpotential test, also known as the 3point or 3pole test. Fall of potential ground resistance test report form. 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. 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.
The 3point or fallofpotential method is used to measure the resistancetoground of existing grounding systems. The attached rod technique better than fallofpotential ground. This provides for the removal of the foreign potential as quickly as possible. What you should know disconnect the grounding system from the substation equipment. 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. Fallofpotential testing with the ground resistance. Checking ground electrode impedance for commercial. Grounding tests are mainly used at lightning protection systems, electrical.
In this video, we demonstrate how to perform a fallofpotential test on a grounding rod. This method uses three poles where the potential difference is measured on points x and y while current is applied in points x and z. Checking connection resistance leading up to the electrode before testing the electrode, start by checking its connection to the facility bonding system. While not as accurate, but very close to the accuracy of the fallofpotential method, the aemc instruments are the best substitute for a fallofpotential test. Why is the ieee standard 81 fallofpotential grounding test important. For a fallofpotential grounding test, youll use four electrodestwo current electrodes named a and b, and two potential electrodes named m and n. The fall of potential test is for measuring the efficacy of a ground rod, eg. The threepoint or fall of potential method is one of the techniques carried out to determine ground resistance. Ideal earth ground resistance tester 2 or 3point fall of potential testing. This method is, in many ways, similar to ground testing using the fallofpotential test. How to perform a fall of potential test w aemc model 3640, 3. Lem norma gmbh also has instruments that perform very accurate testing without using the three point, fallofpotential method.
A test current electrode c is driven into the earth to permit passing a current into the electrode to be tested. A fall of potential test is the most general of methods for meeting the above criteria. Fluke corporation checking ground electrode impedance for commercial, industrial and residental buildings. For a fallofpotential grounding test, youll use four electrodestwo current electrodes named a. Ground testing faqs transcat test, measurement, and.
A second auxiliary test probe, s, is driven into the ground between e and h to measure electrical potential voltage. Connect one current and one potential lead to the grounding system, and the other end to one current a and. With reference to fall of potential, three points of contact are made with the soil. The ground tester calculates the loop resistance of the ground earth. As part of the agreement, you must routinely test the pole grounds on parking lot lighting. However, a test may be performed with the clampon test meter, or on a part of the ground system may be possible. The attached rod technique better than fallofpotential. Fallofpotential testing with the ground resistance tester model. The threepoint method is the most thorough and reliable test method. Some models may also provide automated data reporting.
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. On april 14, 2002, a ground resistance test was conducted to compare the results obtained from the fallofpotential 3point testing method to the clampon. A new customer has just awarded you a service contract to perform standard electrical maintenance for a large suburban mall. Fall of potential test voltageresistance rises dramatically. Technical assistance 800 34391 fallofpotential ground testing clampon ground testing comparison recently, a ground resistance test was conducted tocompare the results obtained from the fallofpotential 3point testingmethod to. How to do electrical grounding system testing fallofpotential method or 3point test.
During the last decade, a new technology appeared in the market, in the form of the clampon ground tester. Fallof potential ground testing and clampon ground. Fall of potential ground test tyron power services. The fall of potential test can be labor intensive and time consuming. On april 14, 2002, a ground resistance test was conducted to compare the results obtained from the fallofpotential 3point testing method to the clampon testing method.
But the site has acres of asphalt and concrete roadway or pavement, with little soil except whats around the. First, the earth electrode of interest must be disconnected from its connection to the site. Browse online, or one of our applications engineers can help you choose the right product for your application. Fall of potential test voltageresistance rises dramatically i can not seem to make sense of this common drawing. Second, the tester is connected to the earth electrode. Measurement of earth resistance by potential fall method.
With reference to fall of potential, three points of. 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. 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.
Finally, the aemc model 3731 was used to measure the resistance at rod number three with all other rods detached from. The two primary requirements to successfully complete this test are the ability to isolate the grounding system from the utility neutral. An overview of the ieee standard 81 fallofpotential. The 3point test is evaluated by plotting the results as data points with. Msha technical reports ground resistance testing in. Ieee industry applications society atlanta chapter january 19, 2010 meeting.
Connect one current and one potential lead to the grounding system. The grounding system consisted of four copper clad rods installed in an approximate 20 ft square. One such test is the fall of potential or threepoint test. The same test was repeated using the aemc model 4630 fallofpotential ground tester. It is important to make sure that the ground resistance around an energized system is functioning correctly in the event of an arc fault. Most commercially available instruments used to measure the ground bed resistance require the ground conductor to be disconnected and the power system disconnected for safety reasons. Fallofpotential method electrical power generation.
The fall of potential method depends upon a test current from a source to a single ground point, from which resistance can be calculated. 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 ground ring surrounding each building is bonded to the ground ring of at least one other building, so that all rings are bonded to each other. In the dead earth method, contact is made at just two points. With this test method, two clamps are placed around the earth ground rod and each are connected to the tester. The most common methods of measuring the resistance of an. Annex c theory of the fall of potential method annex d bibliography. Home technical articles the attached rod technique better than fallofpotential ground testing method. The most commonly used method of measuring the earth resistance of an earth electrode is the 3point measuring technique shown in figure 1.
This test requires a 3point ground resistance tester such as aemcs 4620 or 4630 ground resistance tester. Is it possible to conduct a standard 3point fall of potential test at each building, and obtain a reliable result, despite the presence of the ground rings associated with the other. Remote earth is normally assumed to be at zero potential. Fluke 16232 geo earth ground tester with 34pole fall. Take measurements at voltage probe distance intervals of a maximum of 50 m for a distance of 300 m from the newpcc facility. An overview of the ieee standard 81 fallofpotential grounding. The grounding systemconsisted of four copper clad rods installed in an approximate 20 ftsquare. Using ohms law, eri or rei, you can obtain the ground stake resistance.
This voltage varies along the path between e and h. The measurement of earth resistance is made by the potential fall method. How can you perform a ground test when you cant drive a spike. This is a quick and easy way to calculate ground resistance and document fall of potential testing, with all pertinent fields already included in the premade fall of potential test template. In the figure shown below e is the earth electrode under rest, and a is an auxiliary earth electrode positioned so that two. Fallofpotential testing is extremely reliable, highly accurate, conforms to ieee 81 and gives the operator complete control over the setup. You can also customize the fall of potential test template to add more fields if you deem necessary. A theoretical concept that refers to a ground electrode of zero impedance placed an infinite distance away from the ground under test. A common method for measuring the resistance of a grounding system is the fall ofpotential test, also known as the 3point or 3pole test. Fall of potential testing otherwise known as ground resistance testing measures the capacity of an earth ground system to dissipate energy from a particular site. The fallofpotential method is often referred to as the three point method. This can be estimated by the fall of potential, or impedance method current transformer. If unable to isolate the ground, an actual fall of potential test is not possible. In this situation with multiple paths to ground, the test current will flow to all four ground points at the building corners.
A ground potential rise study is the process of automated timed andor continuous resistanceto ground measurement. The object of a ground electrode resistance impedance measurement is to determine a value to remote earth. However, if there is only one path available for the electricity to pass to ground, stakeless testing wont work. The ideal 61796 earth ground tester performs 2point and 3point fallofpotential or simplified ground resistance testing when it is not possible to use auxiliary ground stakes, and measures ground voltage for new and existing buildings, structures, equipment, and electrical systems. To measure the the resistance of the tmgb to building electrode, you need a special ohmmeter such as the one made by megger the same instrument that also does fall of potential tests in a different configuration. These dedicated systems use the induced frequency test method to continuously monitor the performance of critical grounding systems. Because of the two different electrodes in moderately close proximity you would disconnect one while testing the other. Fallofpotential test form page 1 of 3 project facility. Ground resistance depends on grounding electrode selection, soil resistivity, soil contact, and other factors. The fall of potential method requires auxiliary ground rods and approximately two hours to complete the 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. Guide for measuring earth resistivity, ground impedance, and earth surface potentials of a grounding system. This method involves passing a current into the electrode to be measured and measuring the voltage between the ground electrode under test and a test potential electrode p. This testing device was developed specifically for improving the speed and convenience of the ground test.
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