I work in an old steel mill in PA and most of our substations have ungrounded delta transformers. What brought me to this thread is that I'm trying to understand what is the code on EGCs for ungrounded delta systems? We bring 46kV into the plant and distribute 6.9kV around the plant to the substations mostly via underground PILC cable. When these lead cables blow and we replace them with dry cables, we're already usually over our conduit fills because the old lead cable is a much smaller diameter. Then til you add a ground wire, the conduits are really full. We've had contractors insist on pulling a ground wire with the current carrying conductors in the past because of 250.186. In order to get everything to fit in the existing underground conduits, we usually have to reduce the cable size. Fortunately we can get away with that in some places but in others, we need to maintain that capacity of the existing PILC cable. When I read 250.186 it says, where an ac system operating at over 1000 volts is grounded at any point, a grounded conductor shall be installed and routed with the ungrounded conductors to each service disconnecting means and shall be connected to each disconnecting means grounded conductor terminal or bus. But if the system is ungrounded (and there are equipment grounds present to grounding electrodes at each substation) is the EGC needed? What purpose does it serve other than bonding unitsub to unitsub? None of the old PILC cables have a ground wire pulled with them in the conduit. If anyone has run into this and can point me to a particular NEC article I would appreciate it.
