Man, I see the speculating goes wild when the sparkies arent around!
The common misconception folks have, including in this thread, is that ground rods and grounds/EGCs(equipment grounding conductors) serve the same purpose. I think its has to do with both having the same word- ground! I probably should copy this for future use as I've repeated it over and over again!
Ground rods are for grounding lightning strikes ONLY! On the other hand, grounds/EGCs are for safety and allow breakers the ability to clear ground faults, such as when the windings in a motor short to the frame. If the ground wire wasnt hooked up and bonded to the motor frame, then all metal touching the frame becomes energized which has the potential to shock someone! The same concept applies to subpanel feeders- the ground wire is needed to clear possible ground faults on the feeder!
In regards to 3-wire vs. 4-wire-
4-wire is now required for safety reasons. The difference between the 2 has to do with bonding in the subpanel. Say u only have a 3-wire feed and the neutral feeder develops a bad connection. Because the neutral is bonded to the panel enclosure, any metal in the building or between the buildings(if detached) can become energized, functioning as a parallel neutral return path. This can happen even between ground rods by capacitive coupling, though its rare. If the neutral in the sub is NOT bonded, as it ahouldnt be nowadays on new installs, then even if it develops a bad connection somewhere, theres no possiblilty of a parallel return path via metal between the buildings! The same reasons aply to the 3-wire vs 4-wire appliance debate!
So then if i had 2 drops from the power co, one to the house and another to the shop, how would that work as they are from the same feed lines? I understand the bonding part but this ground deal still has me scratching my head.
Most PoCos dont allow more than one drop to a given property. Second, PoCo drops dont have a ground wire, so this topic doesnt apply to service drops!
