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	Subject - Measuring Impedance? JerryB52 How do I go about measuring the impedance of my grounding system at the service? Like from the main to the ground rod ??? Ryan_J The best way is to use the "three point fall of potential" method. JerryB52 Ryan, can you explain this for me. I've never heard of this procedure. rabbitgun http://www.psihq.com/iread/grndsyst.htm You might take a peek at the article in the link. Hope that helps. JerryB52 Thanks Rabbit, the testing is a bit more complicated than I had imagined. stedder Wow rabbitgun, somewhat involved, I think I'll get the equipment and then go into the biz as a system ground tester, then submit a code change to make it mandatory, boy what would that do to the price of a 200 amp service? JimmyDee You can see the reason most forget the testing and add the additional ground rod at the service. Jim rabbitgun http://www.ers.assetweb.com/ I realize that stedders comment may have been a bit tongue in cheek but there are companies out there who offer those services. If you click the link you can then click "field services" to see what these guy's do. I provided them with electricians to open up equipment for testing. It is great work if you can get it. In my area some jurisdictions require 30 day load studies when load is going to be added to an existing commercial building. A few hundred bucks spent on a recording ammeter can turn a tidy profit.