MV cables in 5"C duct bank

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dahualin

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One of our electrical engineers designed 15KV 750KCMIL AL 133% insulation cable in 5"c duct bank. The diameter of 750KCMIL AL cable is 1.90". So the total cross section area of three cables is around 8.5SQIN. The cross section area of 5"C is around 19.63SQIN. So the percent of cross section of contuit for conductors is around 44%, which is larger than 40%. The design has two 5"C in duct bank, one active and one spare. I am wondering if we can put 2 cables in one conduit and 1 cable in the other in order to meet the code requirement. Any comments is welcome. Thanks.
 
Is the cable what the engineer specified?

If it is, I would RFI the engineer and let him make the call.
Either the cable must change or the conduits must change.

If you change to CU then the conductor size can be smaller.
 
dahualin said:
One of our electrical engineers designed 15KV 750KCMIL AL 133% insulation cable in 5"c duct bank. The diameter of 750KCMIL AL cable is 1.90". So the total cross section area of three cables is around 8.5SQIN. The cross section area of 5"C is around 19.63SQIN. So the percent of cross section of contuit for conductors is around 44%, which is larger than 40%. The design has two 5"C in duct bank, one active and one spare. I am wondering if we can put 2 cables in one conduit and 1 cable in the other in order to meet the code requirement. Any comments is welcome. Thanks.
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Putting two conductors in one conduit and one in the other would be a violation of 300.3(B).
 
if the engineer did the design, tell him what the problem is and ask him to provide you with a solution.
 
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