Measuring Earthing resistance for Electrical grounding system

Many equipment manufacturers now require that the grounding system for their equipment must be 2-ohms or less and that resistance-to-ground tests be conducted on the grounding system in order to validate the warrantees on the equipment. The 3-point fall-of-potential method and/or the Clamp-on Induced Frequency Test are used to measure the resistance-to-ground of existing grounding systems.

Resistance-to-ground testing requires highly trained personnel to properly conduct the tests and ensure accurate results. In the past, many of these tests have been found to be invalid due to poorly trained technicians running the tests. Don’t let the warrantees on your equipment become “null and void” due to errors on the part of the people conducting those tests.

The measurement of ground resistance for a grounding system is very important. It should be done when the electrode is first installed, and then at periodic intervals thereafter. This ensures that the ground resistance does not increase over time. There are two methods for testing an existing grounding system.

  • The 3 Point Method Fall of Potential test
  • The Induced Frequency test or clamp-on method

Ground-impedance measurement are made :

  1. To determiine the actual impedance of the ground connections
  2. As a check on calculations
  3. (3)To determine (a) the rise in ground potential and its variation throughout an area, that results from ground fault current in a power system, (b) the suitability of grounding connection for lightning protection, and the suitability of grounding connection for radio-frequency transmission at a transmitter.
  4. To obtain data necessary for the design of protection for building, the equipment therein, and any personnel that may be involved.

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