I have a separately derived system with a 16kV-480Y277V, 2500kVA transformer. The secondary is connected to a 480V Switchboard Main Breaker approximately 150 feet away. The secondary connection is made up of seven 5-inch PVC Sch 40 conduits, each containing three 750kcmil Cu THHN phase conductors and one 750kcmil Cu THHN neutral conductor.
The neutral conductor will be grounded at one point at the transformer neutral (like Exhibit 250.13 in the Handbook). I am trying to size the system bonding jumper conductors that will run in the conduits with the phase and neutral conductors.
According to 250.102 (C) in the 2005 NEC, I have taken 12.5% of the 7 750kcmil conductors to get the size of the system bonding jumper: 0.125 * 7 * 750 = 656.25 kcmil. I interpret the last two sentences of 250.102 (C) to mean that this is the total cross-section required, and that I can run a bonding jumper in each conduit sized for the conductors in that conduit - this would work out to a 1/0 in each conduit, but the minimum size per 250.66 is 2/0. Is this the correct interpretation or do I need to run a 750 (the next size up from 656) in each conduit for the system bonding jumper?
The neutral conductor will be grounded at one point at the transformer neutral (like Exhibit 250.13 in the Handbook). I am trying to size the system bonding jumper conductors that will run in the conduits with the phase and neutral conductors.
According to 250.102 (C) in the 2005 NEC, I have taken 12.5% of the 7 750kcmil conductors to get the size of the system bonding jumper: 0.125 * 7 * 750 = 656.25 kcmil. I interpret the last two sentences of 250.102 (C) to mean that this is the total cross-section required, and that I can run a bonding jumper in each conduit sized for the conductors in that conduit - this would work out to a 1/0 in each conduit, but the minimum size per 250.66 is 2/0. Is this the correct interpretation or do I need to run a 750 (the next size up from 656) in each conduit for the system bonding jumper?
