If one gets "creative" with raceway isolation, then two equipment-ground conductors are needed—one for the box and one for the receptacle.
These O-Z fittings seem to have been around decades before the "isolated ground" concept went mainstream, and they are specifically intended for conduit applications...no PVC-plumbing kludges here
! http://www.o-zgedney.com/PDF/DA1thru6.pdf page 6 for ICC-series couplings.
I think the whole I-G voodoo noise-suppression thing is way overrated. I-G stuff will not fix poor-workmanship signal-ground loops, but I think some expect it to.
