Another ETAP/SKM modeling question of UG ductbank

[Bugman1400]

When modeling the ampacity or de-rating of LV cables in an UG ductbank, does the cable lose ampacity as you go deeper into the soil? I figured the soil temperature dropped as you went deeper but, the software seems to indicate otherwise. I suppose it depends on locale.

Also, do most folks model the UG ductbank with or without the neutral conductor? Do you assume a balanced load or some percentage of unbalanced load which would cause the neutral to carry current?

 

[charlie b]

I haven't used either of those programs for UG ductbank ampacities. I have used AmpCalc, but that has been a while. My (fading) memory tells me that the deeper you go, the harder it is for the heat being generated in the conductors to dissipate. So ampacity drops as you go deeper.

When using AmpCalc, I never included the neutral in the model. But I don't think it matters. I did a math problem long ago and proved that the heat generated by three balanced phase conductors would be higher than the heat generated by the same three conductors, this time unbalanced, even when you I include the heat generated by the unbalanced current in the neutral.