Low voltage (208/120) direct buried cable

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sespllc

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I want to direct bury 2-5 wire -4/0 cables w/7AWG ground in a 3 ft trench. The voltage is 208/120 3P. The circuits are 400amps/line. I want to separate the cables in the trench by at least 8". I can find derating for the HV 2000 and above for direct bury, but nothing directly, if any, is focused on LV. Is there a spec for this type of installation? We Power Engineers differ in our own office on whether it is necessary or we should just use the HV ratings.

sespllc, PE in Afghanistan
 
I believe you are subject to the same derating factors as wires in conduit I would use 310.15(B)(2). Now how much space is needed between the conductors, to avoid derating, is a good question. All the NEC will give us is to maintain spacing.

I would think that your 8" spacing is more than adequate.
 
is this supposed to be nec compliant ?(if so, what year of nec is this area of afghanisthan using ?) or nesc ? who is ahj ?
 
Yes, it is suppose to be NEC Compliant; w/all the excutions of soldiers in Iraq while takng showers, the Mil is ensuring all installations are certified NEC compliant; seems like a reasonable; therefore, all of the Companies taht hired no nothing engineers and electricians from foreign countries will have alot of remediation work; allready the workload has tripled sue to this policy.
 
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