Tom, it is actually cheaper for a contractor to drive a second rod than to spend a couple hours or more performing a fall of potential test. Another flaw to testing ground resistance is that a 25 ohm measurement today can be 200 tomorrow.
Trekkie, the reason for the 25 ohm standard is somewhat elusive, and has been the subject of lengthy discussions on a number of forums.
Think about it, 25 ohms @ 120 v equates to 4.8 amps and would not trip a standard 15 or 20 amp breaker in a residential setting.
Now for one of its two main functions, (the first being a simple ground reference for the Neutral) the same 25 ohms probably would not mean much more than 200 ohms at the voltage level of a lightning strike, it will help disperse it in any case. On the other hand, it will impose a dangerous voltage gradient for a distance around it in the case of a lost neutral.
Hello Pierre, FWIW, I agree with you and Tom as far as an inspector requiring code compliance, my question was simply for conversation.
Roger
[This message has been edited by Roger (edited 12-19-2004).]