AEMC 4620 User Manual
Also see for 4620: User manual
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Contents
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Digital Ground Resistance Tester Model 4620 and 4630 23The measurement of ground resistances may only be accomplished withspecially designed test equipment. Most instruments use the Fall of Poten-tial principle of alternating current (AC) circulating between an auxiliaryelectrode and the ground electrode under test; the reading will be givenin ohms and represents the resistance of the ground electrode to the sur-rounding earth. AEMC® Instruments has also recently introduced a clamp-on ground resistance tester.The National Electrical Code® and NEC® are registered trademarks of the National Fire Pro-tection Association.4.3 Ground Resistance Testing Principle(Fall-of-Potential — 3-Point Measurement)3-Point measurement is used to measure resistance to ground of auxiliaryground electrodes and grids. The potential difference between rods X andY is measured by a voltmeter, and the current flow between rods X and Zis measured by an ammeter.By Ohm’s Law E = RI or R = E/I, we may obtain the ground electroderesistance R.If E = 20V and I = 1 A, then:R = = = 20 ohmsEI201It is not necessary to carry out all the measurements when using a groundtester. The ground tester will measure directly by generating its own cur-rent and displaying the resistance of the ground electrode. |
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