System Separation

[bandylb18]

I have a large trench with 4160 (vfd generated), 480, 120VAC control voltage running in it using rigid steel conduit encased in concrete. Is there a recommended spacing that should be maintained between these three separate voltages? If so what is the recommended spacing? Could someone recommend a technical article that I could read on this subject?
Thank you for your anticipated assistance.

 

[mwm1752]

try this -- its a start of an endless question

http://www.electrician2.com/articles/ampacity.htm

 

[petersonra]

try this -- its a start of an endless question

http://www.electrician2.com/articles/ampacity.htm

this seems to be a thermal answer. I suspect the OP is looking for how far apart the different voltages should be spaced.

IMO, since they are in their own conduits, I do not see any need to add any additional spacing for the <600V stuff beyond what you end up having to do for thermal reasons, or just for mechanical reasons. I am not real familiar with MV stuff, so there may be special rules there.

I seem to recall some code rules about UG duct banks that might be applicable.