When I was working for the Ground Electronics Engineering and Installation Agency in the US Air Force the engineers would use a signal generator and two good meters connected to the ground under test and two separate test rods. The test rods were cut down sectional rods that could have a treaded pipe T and two nipples as a withdrawal handle. You ran the test recorded the current to the 100 foot rod and the voltage at the 62 foot rod and applied the results to a graph. The slope method is laid out in several different publications but I don't know of any that are on line. The reason that you cannot use the 120 volts as your power source is that stray currents present in the earth will throw the reading off. It was a fair amount of work to test that way and it was only done on remote sights when they needed a value and a null balance ground impedance meter was not available. Null Balance ground impedance testers were the state of the art in 1970. -- Tom
[This message has been edited by tdhorne (edited 10-13-2002).]
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
Most guys here in northern NJ just drive the 2 ground rods. I have had several EC's who just drove in 1 ground rod. If they did though, they left me a reading from a grounding type tester stating that there was 25 ohms or less to ground. Some of the grounding testers do use paper print outs.
Harold: Yes, we accept the readings from a ground test on the EC's letterhead. It should have some details; meter used, date, readings, test locations, etc. John
PS: Still think IMHO, it's easier to drive two rods; case closed.
