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How to Verify Ground Grid and Rod Installation


In Article " How to Calculate Ground Resistance ", I explained the following points:

  • How to Measure Ground Resistance,
  • How to Estimate Minimum Ground Grid Resistance,
  • How to Estimate Upper Limit of Ground Resistance.


Today, I will explain Practice#2: How to Determine Ground Resistance and Practice#3: How To Verify Ground Rod Installation as follows.


You can review the following Articles For more information:


















Follow the steps in this work aid to determine if the materials and connections used for the ground grid are correct as follows:

  • Verify that the grid wires are a minimum of 70 mm2 (2/0) bare copper wire.
  • Verify that the conductors are stranded for 35 mm2 (2 AWG) wire or larger.
  • Verify that the wires are tinned when the soil resistance is less than  70 Ω/m.
  • Verify that the connections of the grid itself are made by thermite welding, brazing or approved compression connectors.
  • Verify that a grid is located at the largest concentration of kVA rating and extends to or beyond the substation switchyard area.
  • Verify that the grid is buried 18 inches (0.5 m) minimum, except where rock-beds occur.


Note: 
 
Numbers 4, 5, and 6 can only be accurately performed before or during installation of the grid, or at excavation. A post-installation verification can only be made from previous layout drawings and notes.






Exercise for Verifying Ground Grid Installation

Question#1: What is the minimum size conductor to be used for a ground grid?
Answer: 2/0 AWG or 70 mm2 copper wire

Question#2: What type of connections should be made for the ground grid itself?
Answer: Thermite welded, brazed, or compression connected

Question#3: If the soil resistance is 65 Ω/m, what requirements should be met for the ground grid?
Answer: The wires should be tinned.

Question#4: Where should a substation ground grid be located?
Answer: At the largest concentration of kVA, extending beyond the substation switch yard

Question#5: What is the minimum depth a ground grid should be buried?
Answer: 18 inches (0.5 m)






Practice#3: How To Verify Ground Rod Installation












Follow the steps in this work aid to verify correct ground electrode (rod) placement and use as follows:

  • Verify the rod diameter and material composition. minimum required is 5/8 inch (16 mm) made of copper clad steel, solid copper, or that stainless steel is used when the soil resistivity is less than 70 Ω/m.
  • Verify the length of the rod at pre-installation or by ground layout drawing, if available. minimum required is 8 feet (2.4 m).
  • Verify that electrodes are flush, buried, or protected against physical damage.
  • Aluminum electrodes are not permitted. Any located on site should be duly noted.
  • It may be necessary to measure a single ground rod’s resistance as a spot check, or one that is suspected of being out of tolerance.
  • If this is the case, follow this basic procedure:

  1. Determine ground rod location to be measured.
  2. Make sure all safety precautions are taken before disconnecting the rod from the grid system. Follow the procedures for lock-out and hold tagging, where required.
  3. Disconnect the grid wire that is mechanically attached to the rod to isolate the rod.
  4. Follow procedures for ground resistance measurement using 
  5. 100 to 125 feet (30.5 to 38.1 m) as the distance for the current probe.
  6. Record the measurements.






Exercise for Verifying Ground Rod Installation

Question#1: What are the minimum rod size requirements?
Answer: 5/8 inch (16 mm) in diameter and 8 feet (2.4 m) minimum in length.

Question#2: If the soil resistance is less than 70 Ω/m, what rod requirements should be met?
Answer: the ground Rods must be stainless steel.

Question#3: What are the procedures for measuring the resistance of a single rod?
Answer: The method to measure individual rod or small grids resistance is similar to measuring system Resistance ground, with these differences:

  • The current probe distance of the test setup is 100 to 125 feet (30.5 to 38.1 m). It can be longer but, in most cases, it does not need to be.
  • An electrode has to be isolated (disconnected) before any measurements are performed. This is especially true if a test is being conducted on an individual rod at a residence.





In the next article, I will explain Other Practices for Inspection of ground Grids, Rods, and Fence grounds. Please, keep following



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