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Metric Cable Derating

Metric Cable Derating

Metric Cable Derating

(OP)
Does IEC 287 or other IEC standards require derating Direct Buried 3/c Medium Voltage Cable based on thermal conductivity?

RE: Metric Cable Derating

Yes

RE: Metric Cable Derating

(OP)
cuky200
Could you elaborate how the derating is calculated? Is the Neher-McGrath method used?

RE: Metric Cable Derating

IEC-287 method evolved from the Neher-McGrath method using the same thermodynamic fundamental basis. Both methods employ the application of thermal equivalents of Ohm's and Kirchoff's Laws of thermal resistance circuit. Notice that conductivity is the inverse of resistivity.

The main differences in both methods are the units system used (English vs. SI/metric). Also the IEC method includes new developments of cable laying, configuration and drying soil effect due to heating by loaded power cable. Another standard, IEC 853-1 & 2 supplement IEC-287 covering cyclic load and emergency ratings.

See the enclose links for information regarding thermal resistance consideration in IEC 287.

http://www.summit.com/toolbox/techinfo/techdocs/ampacity.asp
http://www.elect.mrt.ac.lk/IEE2002powercables.pdf

RE: Metric Cable Derating

(OP)
cuky2000
Thanks a lot. That's just what I needed.

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