If there is no concrete floor, no equipotential plane is necessary.
The primary reason a equipotential plane is necessary is because of the distance between legs of animals like horses or cattle. If there is voltage gradients in the floor they have a longer "base" as well as twice as many points of contact as people so they can stand there and span over a larger voltage gradient much easier than a person can. This has been known to cause production problems in dairy cows, and they are much more likely to have more electric powered equipment in their vicinity than many other animals usually have. Sometimes enough current flows that cows feel it and they will just stay away from certain areas because of that. Not good if the area happens to be a zone around a water tank that has a fault in it, they will just stay away from the tank and will suffer from lack of water because they feel the current before they even get close enough to think about taking a drink.