Bonding subpanels and ground loops

Hello,
I have the following situation with the equipment grounds in my house (USA), and I am wondering whether it is OK. In particular, it seems like there is a "ground loop", although I don't understand the precise definition of that term, or why it is bad.
Main Panel Ground in 1/0 SER Neutral/ ---------------------- Subpanel Ground Ground Bar \ Bar / | \ | / | \ | / | \ | Water Ground \ | Service Rod \ Clamp | Ufer ------------ Ufer Ground 1 Ground 2
Should I nix the Ufer ground connection at the subpanel? As the diagram suggests, each Ufer ground is a separate 20' length of bare copper wire, but they are clamped together inside the concrete foundation. FWIW, I plan to make the main panel a simple disconnect and make the subpanel the primary load center, although I believe that distinction is immaterial under the NEC.
Thanks, Wayne
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All of the grounding electrodes (water, ground rod, Ufer 1, Ufer 2) should be connected to the neutral busbar in the _main_ panel. Bond the neutral to the panel enclosure in the main panel (usually with a supplied green screw). Since the Ufers are connected together, disconnect and remove the Ufer 2 grounding electrode conductor from the subpanel. Then be sure that there is a 4-wire feeder {2 hots (black and red) , 1 neutral (white) and 1 equipment ground (bare or green wire, or a metal conduit)} from the main panel to the subpanel. Do _not_ bond the neutral to the panel enclosure in the subpanel. The neutral must be isolated or "floated" in the subpanel.
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You could leave the second ufer connected as long as the grounding conductor between the two panels is sized for the service rating, not the sub panel rating. It is called a supplemental ground. Used a lot for achieving low ohms to ground <5 for very sensitive electrical equipment. I have connected 100 ground rods together using this method. Hopefully your ufers are more than 20 feet a part.
The problem with ground loops is that current could carry through the earth and not trip out the serving circuit breaker. This is more of a hazard to living creatures than equipment. Cows die in fields during lightning strikes because of the difference in distance in their feet. (more than a meter). It is called the step potential. Soars has an excellent book on grounding. Available at the public library. Put the subject into terms and pictures that are understandable.
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