Table III-l. Ampacities of Aluminum and Copper 

 Cables in Underground Ducts, 20°C 

 Earth Temperature^ 







Cross- 





Metal 



Size 

 (Mem) 



Section 

 Area 

 (in 2 ) 



Ampacity* (amperes) 



3 Conductors per Duct 



5 kV 



35 kV 



Aluminum 



250 



0.196 



264 



274 





500 



0.293 



397 



406 





1000 



0.784 



588 



595 



Copper 



250 



0.196 



338 



351 





500 



0.392 



503 



516 





1000 



0.784 



720 



736 



75 percent load factor, compacted strands (non- 

 circular cross-section) . 



21 



