Do underground feeders need to be derated?

[l3city]

Hi fellas,
During a conversation with another fella, we were debating as to wether underground feeders shall be derated wether in conduit or not by table 310.16 'temperature Correction Factors table'. Of course, underground temperature is not going to be the same as if the feeder is exposed to direct sun light, but still (in Arizona) the temperature gets high. Do we have to apply the temperature corrections factors for underground feeders? How about when the feeder is withing a ceiling space (where temps get high also)?
thanks ahead for any input

 

[iwire]

If you believe the soil to be above 86 F you need to apply temperature correction.

 

[ron]

Many underground feeders require derating due to the conduit's ability to shed heat. Sometimes it is just a matter of whether the conduit is in cement, sand, stone, etc. which effects how much heat it can dissipate.

 

[SEO]

Adjustment factors are required for underground conductors. Section 310.15(B)(2)(a) single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than (24 in.) and not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Section 310.15(B)(2) exp No. 4: Derating factors shall not apply to underground conductors entering or leaving an outdoor trench if those conductors have physical protection in the form or rigid metal conduit, intermediate metal conduit, or rigid nonmetallic conduit having a lengh not exceeding (10 ft) and if the number of conductors does not exceed four. Other adjustment factors apply as well, temperature, conduit fill etc.