The equipotential bonding grid is different than the grounding electrode such as being discussed here although what Randyj is describing with his ground rods at the pier is almost a equipotential grounding grid.
It is his conception that the branch circuit supplying the pier is somehow losing current to earth that is wrong.
You got pretty close there JW but I'm not saying that the circuit supplying power to the pier is losing current to earth. I'm saying that it loses voltage due to the distance from the switch box panel. If the ground wire comes all the way from the switch box hundreds of feet away there is a difference in voltage between the ends of that ground wire and a difference between that ground wire and the ground rod at that distance. This is why that ground wire back to the main switch panel must be cut and a ground rod installed at the walkway entrance. If this is not done then there is a very measureable voltage between the dock and the water. I have in fact touched one lead of my volt meter to a dock then dropped the other end in the water and got an 8 volt reading but when I disconnected the ground wire going back to the switch box panel the reading dropped to zero. The ground rod configuration may or may not protect equipment/appliances and may not even throw a breaker but it will save lives because the current path is then through the metal dock bonded to the ground rod. I may not understand the description of equipotential grounding but I do understand zero voltage and zero current and I know how to detect them.