Sorry if this is lengthy but it is neccessary. I have several problems but will tackle them one at a time (all electrical and not emotional or personal).I have a 1500 kva 3phase xmfr that feeds a 4000A MDP. Their are 10 sets of parallel feeders from the xmfr to the MDP. The primary feeders are 500kcmil w/ a 350kcmil grounding conductor (neutral) with NO grounded conductor in each conduit (PVC). The MDP is not connected to a ground grid system but is bonded to building steel w/ a 3/0 copper. The NEC 2005 Table 250.122 shows that the neutral is undersized (4000A) and 310.4 also states the grounded conductor " must be the same size in circular mill". Is it mandatory that all service entrance conductors (parallel feeds) have a grounded conductor included and is the neutral undersized according to my understanding? Also, I have been experiencing severe problems with equipment that rely upon electronic boards that are constantly frying ( motors with variable speed drive VSD). Since much of the metal raceway that runs throughout the facilty do not have grounded circuits included in the branch feeders, but rely solely upon the metal raceway as grounding, could this be causing transient voltages to be applied back on to the PC board and blowing circuits. The facility is 30 years old and with 8 overhead cranes running along a rail system 12 hours a day, much of the counduit has vibrated loose from the connector, coupling, walll etc. thus loosing it's continuity and ground fault protection. Any help is greatly appreciated and thank-you.