A contractor runs PCV to a detached building. Proper sizing, three wires and has a ground rod at the building. I give him a red tag for Article 250.52 (NEC2005) in which a lively debate starts. When you run a sub-panel 3 wire feed or 4 wire feed. I always run 4-wires plus a ground rod. What do you guys think?
Joe, although I would run an Equipment Grounding Conductor because of preference, it is not required if 250.32(B)(2) applicable.
(2) Grounded Conductor Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in each building or structure involved, and (3) ground-fault protection of equipment has not been installed on the supply side of the feeder(s), the grounded conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of either of the following: (1) That required by 220.61 (2) That required by 250.122
Question: As Roger points out, if there is no grounding conductor run with the feeder, the grounded conductor is used to bond metal frames, etc....does this mean that the neutral bar is not insulated/isolated from the ground bar as it would be if this subpanel was located in the main building where the service is located?
Even the IAEI, when they presented this application to three of it's own experts, got four answers!
Codewise, the guy can probably get away wit only a ground rod, treating the feeder as if it were a separate service.
I am something of a simpleton, and like to consider the "service" to be where the PoCo drops in, with everything from that point to be part of the same system. But I can see where the code might not limit me to that approach.
In my construction days I always ran four wires. I learned fast that just because the contractor does not do it like I do means it is incorrect. Yes red-tagged always give lively debates but I always call the contractor when it is going to cause extra work and money. I gave him a white/purple sticker, that is what New Jersey gives out when the final passes. Thnaks for all your feed back