This is what the army has to say on the subject. couldn't get the pic to come up, but it shows a megger with the one lead on the ground rod, the other on the water pipe.
-3. Resistance. The resistance between a grounding rod and the earth should be less than 25 ohms. Check the ground resistance with a megohm meter (Figure 1-12). This check should be made with the grounding jumper between the water pipe or a good ground and the electrical system. A metallic cold-water system makes a good point for testing the resistance of an electrical grounding system. If 25 ohms to ground cannot be achieved, take the following actions:
following actions:
Figure 1-12. Megohm meter
a. Drive additional 8-foot grounding rods into the earth and bond them together. The rods must be at least 6 feet apart (Figure 1-13).
[This message has been edited by trekkie76 (edited 12-11-2005).]
