Buried Cable below 600V

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jhdeakle

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Using NEC 2005 & 2008, I can not find a spacing requirement for direct buried cable below 2000V's.

I have a large number of 480V, 3/C, TC type (approved for direct burial), power cables that will be installed in a trench. Sec. 300.5 gives me depth info. but I do not see where there is any spacing requirement similar to sec. 310.6 for 2001V to 35,000V's.

Does anyone have any advise or maybe show me the sec in the NEC that would address this?

Thanks!

JD
 
I do not believe the NEC deals with your situation for the differences in voltage.

Are these different voltage cables utility service cables or are they private high-voltage cables.

There is probably some info about the spacing of high-voltage and low-voltage cables in the NESC.

The closest you may get to this in the NEC that I am aware of is to look at 300.3(C)(2). Only this subsection does not mention trenches.
 
You may need an engineering calculation of the ampacity or required spacing to avoid heat damage if they are all power cables. Table 310.16 does not specify the spacing required, but if spacing between the buried cables is not maintained, they they must be derated per Table 310.15(B)(2)(a).
 
Thanks for the replies!

These are private power feeds for 480V motors in the Oil and Gas industry.

It looks as if you guys have read every thing I have in the code. As you pointed out, I had derated as required and looked into spacing as far heat build up. Using the rules for 4/0 and larger when installing into cable tray I am allowing a bit more space for larger cable.

From this point I will assume there no "Code" requirement for cable spacing below 2001V when buried. I tried to get the client to go with MC cable so there would be no question but the expense won out. I think a common since approach used with the NEC will have to do. Maybe, also, some the rules associated with 480V tray loading will help support my final installation drawings.

Thanks for the help.
 
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