Mar 12, 2017 terminating cat6 shielded cable with a standard rj45 connector. Such audits are essential to comply with current health and safety legislation, including bs7430, as well as to protect your assets and personnel. Proper grounding of instrument and control systems in. The resistance of the surrounding earth depends on the soil resistivity. This method is referenced in all the electrical installation testing standards and can be used to measure the earth resistance both accurately and safely. An understanding of the soil resistivity and how it varies with depth in the soil is necessary to design the grounding system in an electrical substation. How earth resistance is measured the term earth resistivity expressed in ohmcentimeters abbreviated ohmcm is one basic variable affecting resistance to earth of an electrode system. Earth injection testing is a test of the earthing system and conducted to measure the risk of earth potential rise epr where a large current flows to earth through an earth grid impedance. The clamp method requires a complete electrical circuit to measure. Then the total resistance of the ground system can be determined by calculation. Earth resistance testing the faults in any electrical resistance testing are unavoidable. When we measure the resistance, this is the actual resistance of the ground field plus the parallel path of the mgb.
The resistance area of the earth electrode is the area of the soil around which a voltage gradient is measured with a commercial instrument. An earth electrode and earth electrode resistance are defined in bs 7671 as. How earth resistance is measured instrumentation tools. The resistance offered by the earth electrode to the flow of current into the ground is known as the earth resistance or resistance to earth. Measurement of earth resistance the measurement of earth resistance is made by the potential fall method. A simple way to measure the earth resistance is to drive an auxiliary earth electrode c, into a point distant from the grounded earth electrode under test e. Earth resistance measurements on installations with a single earth electrode it is important to point out that the earth resistance measurement of reference is the 2stake method. Principles and testing methods of earth ground resistance.
With the stakeless test method, the fluke 16232 is able to measure earth ground loop resistances for multigrounded systems. Overview of different methods of testing earth electrodes to ensure their impedance is low enough. Earth pit testing is measured by megger or earth pit tester. It is a critical factor in design of systems that rely on passing current through the earth s surface. Proper grounding of instrument and control systems in hazardous locations joe zullo regional sales manager. This method is derived from the 4point method which is used for soil resistivity measurements.
Leon markwell, senior engineer at the iet, discusses the inspection and testing of earth electrodes. Substation earth pit resistance tester at rs 576000 piece. Resistance of earth is the resistance between infinite earth and earth electrode. O application soil resistivity and ground resistance measurement o range. Earth resistance measurement earth resistance measurement with 4, 3 and 2 wires and six ranges covering measurements from 0. The operator has no probes and therefore cannot set up the desired test circuit. Earth pit resistance testing services grounding system audits are designed to test your protection systems to ensure that they will operate effectively during a fault. Earth pit resistance is measured by earth tester, earth tester have four terminals p1,p2,c1,c2 i. Figure 1 displays the fluke 1625 earthground tester. 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. It is the resistance of soil to the passage of electric current.
Measuring earth resistance with fall of potential method photo credit. Actually, the earth is a relatively poor conductor of electricity compared to normal conductors like copper wire. Ground resistance depends on grounding electrode selection, soil resistivity, soil contact, and other factors. Measurement of earth resistance by potential fall method. Earthing and earth grid testing rans electrical high. Place the sensing clamp around the ground cable leading out to the ground field. My friend i am sharing my hands on experience you can use bentonite in addition to common salt and charcoal to improve earth resistance values it may sound funny but its true i have used cow dung to fill up the earth pit and watered the earth pit over night,next day when the earth resistance was measured it was less than 1 ohm but cow dung works only for a day or two but bentonite works. The threepoint method is the most thorough and reliable test method. Nec 250 specifies the value for a single earth pit the 25 ohm value noted in the nec applies to the maximum resistance for a single electrode consisting of a rod, pipe, or plate. A guide to earthground resistance test kyoritsu india. The most commonly used method of measuring the earth resistance of an earth electrode is the 3point measuring technique shown in figure 1. Soil resistivity is a measure of how much the soil resists or conducts electric current. Earth electrode and earth loop impedance testing theory and applications as two of the most common testing subjects debated amongst electricians as well as generating the highest percentage of calls to the megger technical support desk this series of presentations and supporting booklet hope to clarify some of the obstacles faced by an. The measurement principle involves using an appropriate generator g.
The fluke 16232 earth ground tester measures earth ground loop resistances using only clamps, only stakes, or one clamp and stakes. Earthing in electrical network purpose, methods and measurement. The measurement of earth resistance is made by the potential fall method. Check voltage between earth pit conductors to neutral of mains supply 220v ac 50 hz it should be less than 2. The easiest way to measure ground resistance using clamp. Mtl americas introduction grounding is defined as electrical equipment connected directly to mother earth, or to some conducting body that serves in place of the earth, such as the steel frame of a plant and its. Fluke 16232 earth ground tester performs all four ground tests quickly and accurately. The first two factors can be taken as negligible compared.
The earth or e terminal is connected to the other side of the insulation, the ground conductor. 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. Measurement of earth resistance is a vital part of the maintenance of any electric installation. Earth resistance measurements with 4, 3 and 2 wires earth.
Measuring ground resistance with the 62% method ground resistance is a measurement of the conducting connection between a grounding system and earth. 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. Instead of a solid connection of neutral to earth, a neutral grounding resistor ngr is used to limit the current to ground to less than 750 ma. What is earth pit resistance value the earth images. Each larger shell has smaller equivalent resistance due to more parallel resistances. Because it should be very low ohmically, it should have no real effect on the measured reading. Measurement of ground resistance with earth resistance meter. Ra r r earthground resistance 300k ac resistance 300k dc low resistance 3k change item select start test display menu hc2 sp2 esp1 ec1 4 pole 3 pole 4 pole 2 pole 2 4 off 3 pole 1625earth ground tester st edw001. Hence, a wellmaintained earthing system ensures the proper functioning of protection systems, absorbs electrical noise and provides safety to operating read. The clamp tester measures the complete resistance of the path loop that the signal is taking. The goal in precisely measuring the resistance to ground is to place the auxiliary.
Principles and practice of earth electrode measurements reeve. Jul 27, 2018 resistance of earth is the resistance between infinite earth and earth electrode. If a higher resistance is obtained for a single electrode, a second electrode of any of the types specified in the nec is required. The fluke1625 earth ground tester generates a known current through the two outer ground stakes and the drop in voltage potential is measured.
These test electrodes can be of lesser quality higher earth resistance but must be electrically independent of the electrode to be measured. For example, if you are measuring a circuit having a current that you do not want to include, you connect that part of the circuit to the guard terminal. Stakeless measurement the fluke 1625 earth ground tester is able to measure earth ground loop resistances for multigrounded systems using only current clamps. Earth electrode resistance the resistance of an earth electrode to earth. Mtl americas introduction grounding is defined as electrical equipment connected directly to mother earth, or to some conducting body that serves in place of. P1, p2, c1, c2, it means there are two potential terminals and two current terminals. Figure where it explained principle of operation of earth resistance meter it is an earth that e starts measuring by the measuring method of a left ground. Sep 22, 2016 i thought earth pit was a misspelling or typo. Measuring the resistance of an earth grounding and bonding of electrical earth pit testing in india earth tester working principle your grounding of the power substation what is a good ground resistance valueearth pit resistance testing record sheetearthing in electrical work purpose methodeasurementearth resistancethe most mon methods of measuring resistance an earthearth pit resistance. Principle of earthing measurement this instrument makes earth resistance measurement with fallof potential method, which is a method to obtain earth resistance value rx by applying ac constant current i between the measurement object e earth electrode and c current electrode, and finding out the potential difference v between e and p. Measuring the resistance of an earth grounding and bonding of electrical earth pit testing in india earth tester working principle your grounding of the power substation what is a good ground resistance valueearth pit resistance testing record sheetearthing in electrical work purpose methodeasurementearth resistancethe most mon methods of measuring resistance an earthearth. The function of a sound earthing system is to ensure that all electric equipment are connected to the ground potential. Earth electrode conductive part, which may be embedded in the soil or in a specific conductive medium, e.
Terminating cat6 shielded cable with a standard rj45 connector. The most common methods of measuring the resistance of an earth. The threepoint or fall of potential method is one of the techniques carried out to determine ground resistance. Earth resistance is the resistance of soil to the passage of electric current. Aug 06, 2019 a practical to earth resistance testing stake less earth ground testing from cole parmer earth resistance fall of potential measurement fluke unled earth pit resistance testing services lication usagethe most mon methods of measuring resistance anthe most mon methods of measuring resistance an4 important methods of ground resistance testingearthing in electrical work purpose methods andearth. Earthing resistance tester electrical engineering centre. Getting down to earth 5 4 getting down to earth safety there is an inherent safety problem in earth resistance testing that requires care and planning by the user of the test set. Earthing resistance as per ie rule cr4 discussion thread. The general principle of instrument earth is all individual shields screen and overall shield screen of single or multi pair cable shall be isolated from. The value of the earth resistance for different power stations is shown below. Earth resistance measurements with 4, 3 and 2 wires. Principles and testing methods of earth ground resistance ee.
Km1620 km 1720 singlejaw type earth resistance tester is widely used for earth resistance testing of the equipments in the field of power, telecommunication, as well as the other electrical equipments. A practical to earth resistance testing stake less earth ground testing from cole parmer earth resistance fall of potential measurement fluke unled earth pit resistance testing services lication usagethe most mon methods of measuring resistance anthe most mon methods of measuring resistance an4 important methods of ground resistance testingearthing in electrical work purpose. The ability to properly measure ground resistance is essential in preventing costly downtime due to service interruptions caused by poor grounds. Such audits are essential to comply with current health and safety legislation, including bs7430. The measurement system based on the earth leakage current loop resistance can be applied to the various grounding system arrangements. Renewable futures wanted to bring their new substations online. But the actual value of earth resistivity need not be measured to check the electrode earth resistance. How to reduce the earthing resistance cr4 discussion thread. Using ohms law, eri or rei, you can obtain the ground stake resistance. If there is only one path to ground, the stakeless method will not provide an acceptable value and the fallofpotential test method must be used. This depends upon mainly three factors the resistance of the electrode itself,the contact resistance between electrode surface and soil,the resistivity of soil between the electrode and infinite earth. Mathematically, the earth resistance is given as the ratio of the voltage and the current shown below.
O application soil resistivity and ground resistance measurement. Where v is a measured voltage between the voltage spike and i is the injected current during the earth resistance measurement through the electrode. With the three point method, the c1 and p1 terminals are tied together at the instru. Most earth resistance testers carry out measurements based on the dropofpotential method. A practical guide to earth resistance testing weschler instruments. Clamp on type earth resistance tester leakage current. Fluke 16232 geo earth ground resistance meter fluke. A resistance earth system is used for mining in india as per central electricity authority regulations.
The earth resistance value ohmic value of an earth pit depends on soil resistivity. Megger makes electrical test equipment to help you install, improve efficiency and extend the life of electrical assets and cable networks at high. Fourpoint measurement diagram threepoint resistance measurements the three point method, a variation of the four point method, is usually used when making ground earth resistance measurements. It is a requirement because of the high hazard electricity can pose to people and equipment.
It is a critical factor in design of systems that rely on passing current through the earths surface. Getting down to earth 9 type of soil affects resistivity whether a soil is largely clay or very sandy, for example, can change the. Testing of earth pit resistance the earth images revimage. The procedures for earth resistance testing are referenced in ieee standard no. Earth ground resistance measurement earth resistance meter. It features easy operation, highaccuracy and good adaptation of testing environment. The guard or g terminal provides a return circuit that bypasses the meter. But, if the area of a path for current is large enough, resistance can be quite low and the earth can be a good conductor. The most common methods of measuring the resistance of an. The 3point method, called the fall of potential method.
The earth resistance mainly implies the resistance between the electrode and the point of zero potential. The operator must be certain that earth is included in the return loop. In areas where driving ground rods may be impractical, the twopoint method can be used. Four of the most common methods of ground resistance testing used by test technicians are discussed below.