6.9KV Conduit Spacing in Ductbank

[smkdeb123]

I have a 8 X 3 concrete ductbank, 8 columns, 3 rows, all 4"PVC. Top roll is 6.9KV 3/c-500kcmil, middle roll is all future, bottom roll is 480v MOV power, control, etc. The question is on Figure B 310.3 the voltage only is listed for 0 to 5000 volts, where in the code does it address the separation of conduits based on higher voltages? How about 13.8KV? The top of the duct bank is 30" below grade.

 

[rbalex]

The analogous figure for higher voltages is Figure 310.60. The problem is the various table values (Table 310.67 through Table 310.86) are very specific to Figure 310.60, including spacing.
A few adjustments are recognized in Section 310.60 and Section 310.60 FNP refers you to Annex B. The basic applied formulas are the same; it is the ?constants? that vary.