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Ambient air temperature for underground cable sizing

Ambient air temperature for underground cable sizing

Ambient air temperature for underground cable sizing

(OP)
Tables show derating factors for soil temperature, and ambient temperature, should I consider two derating factors in the case of underground cables? one for soil temperature and the other for ambient temperature? or one only for this type of installations (soil temperature).

RE: Ambient air temperature for underground cable sizing

One only per IEC, determined by surrounding medium.

RE: Ambient air temperature for underground cable sizing

The temperature of the captured air in the duct [it is not so important-usually is taken as 60oC] and the earth temperature [it is the most important] in both calculation methods [IEC 60287-2 and Neher and Mc Grath methods].The air temperature is not involved in underground power cable temperature calculation.

RE: Ambient air temperature for underground cable sizing

First of all it is not from the actual Neher and Mc Grath paper, but from "Calculation of Underground Cable Ampacity” by Francisco de Leon -by-the way it is a very good article, in my opinion. The figure 3 and 4 explain the Neher and Mc Grath general technique by subdivided studied area in layers. So tambiant could be air, ground, water [?] and other temperature.
This paper contains the instructions how to use CYMCAP computer program to calculate ampacity and temperature rise of underground power cable-directly buried or in ducts.

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