Shortform testing info at
http://www.tradeport.on.ca/ApplicationNotes/aemc.pdf It is most often an AC test, to limit galvanic interaction of soil and rod material. The frequency is typically 128 or 135 Hz to reduce sensitivity to 50-60Hz power currents or their harmonics.
For ground mats, the test-lead spacing can be on the order of 1,000 feet/ Modern test sets will indicate excess test-rod resistance of the farthest rod on a 3-point test.
[This message has been edited by Bjarney (edited 05-31-2002).]
