This isn't exactly on topic, but it's related to something I've always wondered:
It seems like everyone talks about earth impedence being less-than or equal-to 25 ohms. That doesn't really make sense to me. How can earth have a definite resistance? Your resistance has to be between two points on a circuit, and assuming the ground rod is A, where is B? And if you increase the distance between the two points aren't you increasing the resistance?
What's going on when people talk about "earth impedence?"
-John
