Call me a fanatic but I would want to drive a stacked rod at the garage and add sections until I got under 25 ohms if the GEC did not show an impedance of 25 ohms or less when run to the electrodes at the house only.
I would not call you a fanatic only concerned with your work.
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I will ask Why?
What is the magic in 25 ohms?
The NEC does not require 25 ohms.
Here is part of a post from a Florida electrical instructor who is also spends a lot of time studying lighting protection systems. His info generally comes from here.
http://www.lightning.ece.ufl.edu/ If you have a normal soil resistivity of something around 4,000 to 50,000 ohm-centimeters, a ground resistance of anything around 15 to 200 ohms will be sufficient for basic lightning protection. Deep rods are of almost no use as lightning typical drives no more than 2 feet into the earth before extending out laterally from its strike point.
His entire post can be seen here.
http://www.mikeholt.com/cgi-bin/codeforum/ultimatebb.cgi?ubb=get_topic;f=7;t=001 802;p=1#000003 Bob
[This message has been edited by iwire (edited 01-03-2006).]
