Cable Separation - Underground

I don't believe that the NEC cares about the separation distance, just to be safe you can run 24 vdc wiring in the same conduit as 120 vac power wiring. I believe that the type instrumentation cable will be more important than the conduit separation. Use twisted shielded pair cable. You can get instrumentation cable that has several twisted shielded pairs to carry several signals with separation.

the twisted pairs will help in cross talk,, ac humm,, but ive found its better to lay in trench about 12-16 inches apart, this depends on the type of load your going to have on the 480v line,, the larger the load the farther apart, yes you can put in the same conduit, if using, but no doubt will get a ac humm on the second line, you can also filter it out, if the smaller line dont use the 60 hz range, there are many factors in the best way to go,, are both lines direct barial,, in conduit,, in a trench, the conduit isnt very expensive, and makes a easy way to add lines in the future,, just over size it to give room and make pulling easy, i would put the 480 in the trench first, at the required code depth, about 20-24 inches (check for your area) then put sand in to bring it up to about 10-12 inches and put second conduit in, then finish with sand, just a thought, a roll of caution tape layed in the trench near the top, might save a accedental misshap with a future project, (find the tape when digging before getting to the conduit), its my 2 cents worth,,good luck

Good question, first there are several studies across the board on EMF noise. Actually it is true that you do seperate these types of transmission lines from high-voltage feeds. It is recommended that you use shielded and twisted paired trasnmission cables in a seperate conduit. Plus for added signal safety, it would not hurt to run the conduit at different elevation from the high voltage lines. From experience in doing underground vault work, the high-voltage lines are usually ran to their own vaults, being a different vault from the communication lines. They can be ran in the same trench on stacked risers, but at different elevations and then split into their appropriate vaults. Good luck.

Per IEEE-518, the required separation distance is 650 mm. A trench separation is notmally treated as tray separation.