NETA Ground Resistance Testing Methods 5

Question 1

When using the two-point method for ground resistance measurement, what does the second reference point typically represent?

Accepted Answer

A water pipe or structural steel with assumed zero resistance

Answer

The two-point method connects the tester between the electrode under test and a convenient reference such as a water main or building steel, assuming the reference has negligible resistance.

Question 2

What soil condition produces the lowest earth resistivity and therefore the easiest ground electrode installation to achieve low resistance?

Accepted Answer

Moist clay or loam soil with high mineral content

Answer

Moist clay or loam with high dissolved mineral content has the lowest resistivity because moisture and ions are the primary charge carriers in soil.

Question 3

A NETA technician is testing a ground rod in soil with high resistivity. Which chemical enhancement method is acceptable for permanently reducing ground resistance at that electrode?

Accepted Answer

Installing a ground enhancement material (GEM) or conductive concrete in the electrode bore

Answer

NETA and IEEE 142 recognize ground enhancement materials such as conductive grouts and GEM compounds as permanent, non-corrosive methods to lower soil contact resistance.

Question 4

In the four-potential method (Wenner array) for soil resistivity testing, what does the calculated apparent resistivity represent?

Accepted Answer

A weighted average of soil resistivity to an approximate depth equal to the electrode spacing 'a'

Answer

The Wenner array measures an apparent resistivity that represents a weighted average of all soil layers from the surface down to approximately the electrode spacing distance 'a'.

Question 5

Why must all parallel ground paths be disconnected or the electrode isolated before performing a fall-of-potential test?

Accepted Answer

Parallel paths provide alternate return routes for test current, causing the instrument to read lower than the true single-electrode resistance

Answer

If parallel grounding paths exist, test current returns via multiple routes, and the instrument measures the parallel combination of all paths rather than the resistance of the isolated electrode.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA Ground Resistance Testing Methods 5