No ground conductor in a sub panel, and neutral/ground not disbonded.

[fastline]

Friend of mine has a 100A sub panel in a detached structure. It currently has two hot and one neutral conductor. I cannot recall if ground has to be carried from the main panel? He was about to just disbond the ground and neutrals in the sub as someone told him he needed to, but I warned that he is then running with zero ground in detached structure and ground should be reestablished.

I have heard of ground loop issues when not carrying ground but I fail to see the concern on a detached structure.

 

[LarryFine]

He should NOT unbond the neutral and ground! For a detached building, without another metallic pathway between them (like a water pipe), this used to be allowed, and is permitted to be retained. There should also be grounding electrode(s)

Without the bond, a ground fault would energize everything that should be (expected to be) grounded.

For new work, a 4-wire feeder must be installed and the neutral/ground bond not be made, as with any sub-panel.

 

[fastline]

I know this guy and pretty sure he is not going to run a ground unless forced to. I am just trying to identify potential risk for him. I told him dropping a ground rod will establish ground potential, but there is no direct conductor path the the service ground if the panel is disbonded.

He currently has a PVC conduit with the conductors but there are at least 3 90s and I don't know if I could actually get anything in there to pull a conductor in. I am also pretty sure he pulled it in dry.

 

[infinity]

As Larry stated this was permitted up until the 2008 NEC. Unless he plans on pulling an EGC in the raceway then he should do nothing with the bonding jumper between the neutral and the metal enclosure. A separate structure is required to have it's own GES (which could be two ground rods) but ground rods have nothing to do with clearing faults, that is accomplished by bonding the metal parts and branch circuit EGC's directly to the neutral.