installing that circuit as a feeder that supplies overcurrent protective
devices he has made work for you with no benefit. If he had simply
installed a multi wire branch circuit to the out building he would have
doubled the available power without triggering the requirement for a
grounding electrode system.



Let me suggest that you install a two pole
switch assembly in place of the breakers now in use and add a ground
bar. This will turn the underground wire into a branch circuit and
relieve you of the requirement to install a grounding electrode system.

Had the CB box been properly installed as a branch circuit with neutral and
ground separate would the additional ground rods be necessary?