While researching info on my ductbank question I found a error in EC&Ms Medium Voltage Power systems book 2th Edition . Page 107 bottom table 310-85 reference table should be table 310-77. Most the answers to my questions were in that book. I have found most electricans and inspectors have very limited knoledge in HV systems but since dergrelation ,it should be addressed a lot more! Thank you for your responses