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Basics Clamp-on Ground Resistance Tester © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 1 of 12 Integrity of the Ground • Three key components of the single ground Electrode – Resistance between Ground Electrode and Clamp, Bonding in multirod applications – Resistance of contact between soil and rod(s) – Resistance of Concentric Shells of earth © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 2 of 12 Integrity of the Ground • Effect of the Soil on Electrode resistance – Soil conditions, and soil types • Sandy soil have higher resistance that clay or loam – Seasonal Environmental conditions which effect both moisture and temperature © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 3 of 12 Integrity of the Ground • Ground Electrode – Typically measured only at installation • In truth very seldom tested by installers. • Only one out of 10 said they test single point ground Electrodes, in an informal survey – Methods of testing the ground electrode • Fall potential test, and Slope method • Ground resistance clamps © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 4 of 12 Test Equipment Clamp-On Ground resistance tester. • The Resistance of the total ground network is now measured. • This is a loop tester and requires the utility return to act in simples terms as the aux rods. © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 5 of 12 Test Equipment Clamp-On Ground resistance tester. • Make sure you have a clean, clear connection of the clamp around the ground. • Select and measure the current, if current is > 5 (this my very from manufacture) resistance can’t be measured using the ground clamp tester. © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 6 of 12 Test Equipment Clamp-On Ground resistance tester. • If voltage (E) is applied to any measured grounding probe R(X) through a special transformer , current (I) flows through the circuit and can be measured , thereby establishing an equation which can be used to calculate R(x) – E/I=RX. If E is kept constant, then through the use of a CT current can be detected and the resistance of the ground electrode circuit my be achieved. © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 7 of 12 Clamp-On Ground Resistance Measurement • R1, R2, ---Rn can be considered as a large parallel resistive circuit. As we know, a large number of resistors in parallel with each other effectively create a resistance value which is lower than the value of the least resistive path. – – – – Here is an easy to understand example of parallel resistance. Simple equation, 1/R = 1/R1 + 1/R2 + 1/R3 + 1/R4. If R1=3.5, R2 =4, R3 = 4.5 and R4= 5, then 1/R=0.285 +0.25 + 0.22 + 0.2, or R= 1.04 ohms. © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 8 of 12 Clamp-On Ground Resistance Test • Advantage is that the ground electrode doesn’t need to be disconnected from the electrical system. • The jaws of the clamp must be placed in the electrical path of the systems grounding wire to the ground rod © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 9 of 12 Clamp-On Ground Resistance Test • This is an example the Clamp-On Ground tester is being used to measure the ground resistance in a street light application • Note in this application the tester is place between the ground conductor and the ground electrode. The loop is between the ground conductor and the parallel path of R1, R2 ---Rn back through the earth resistance. © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 10 of 12 Earth Testers • Ideal/Megger 61-788 – 3 pole Testers • IDEAL/Megger 61-789 – 4 pole Testers – Self powered - no need for hand crank – Low power consumption Compact and lightweight – Quick battery check – Limited lifetime warranty © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 11 of 12 Earth Testers • Ideal 61-920 Ground resistance Clamp – – – – – – Ground Resistance Ground Leakage Current Auto ranging Audible indication < 40 ohms Open jaw indication Data hold © 2007 Ideal Industries www.idealindustries.com Basics Clamp-on Ground Resistance Tester 12 of 12