310.60(C)(2)(b) Conductors rated 2 to 35 kV

[mxstar211]

A few of my co-workers are would like to know why you need to de-rate conductors when you bury them deeper. Does anyone have a good explanation for this? Thanks a lot!

310.60(C)(2)(b)

"Where burial depths are deeper than shown in a specific underground ampacity table or figure, an ampacity derating factor of 6 percent per 300-mm (1-ft) increase in depth for all values of rho shall be permitted."

 

[K2500]

The ability of the soil to dissipate the heat generated by the cable diminishes as depth increases. Soil tempature stability generally increases with depth. Things get hotter and stay that way longer the deeper you go.