Ground Conductor Required between Generator & Load

[Tesla1971]

My question pertains to the codes for the United States, namely the NEC.

I currently have a project where I need to accomplish the following:

Generator - AC Distribution Panel - Load 1 / Load 2 / Load 3

Basically I am employing a 200kW, 600V, 3-phase, 4-Wire Generator in a substation for "essential power".

The Generator will be located in the middle of the substation. It will be connected directly to a 400A, 600V, 3-phase AC Distribution Panel with Main Breaker of 250Amps (about 10 feet away). The AC Panel will also have 3 Feeder Breakers that will connect to 3 Station Service Transformers located throughout substation (between 800-1200 feet away).

The Station Service Transformers will be step-down transformers: 600V-208/120V.

Since I would only need the L-L voltage of 600V (as opposed to the L-N voltage of 346V), I would like to know if I would have to pull a ground wire from the AC distribution Panel to each of the Station Service Transformers?

Or would I only need to pull the 3-conductors for each phase and simply ground everything (generator, AC Panel, Station Service Transformer) individually to the ground grid.

 

[davidbeach]

You don't need to pull a neutral, but should certainly have an equipment grounding conductor (green) with every run. It may be that your conduit can substitute for the green wire (per code anyway, I'd never do it myself), but you can't use the ground grid for your ground. Ground with the phase conductors results in a lower impedance and therefore higher fault currents, and with a generator that small you are going to want to have all the fault current you can get to ensure clearing.