When bolting 4" metal boxes to I beams that are part of a metal building that is grounded are the 4" boxes still required to have a ground attached to the box and to the receptacle? I have all of the ground wires connected to the receptacles but It seems redundant to have to add a pigtail to ground the box to the receptacles when the box is bolted to the I beam and the receptacles are bolted to the 4" box with the mounting screws. If anyone has any input it would be greatly appreciated.