Mixing of cables over 600 volts and cables under 600 volts in manholes is permitted by Art. 300-3(2)(e) if they are "effectively separated". "Effectively separated" is not defined. So far, I have not seen anything in IEEE or other publication to give definition. Some say that Art. 725-54 implies the Code Panel requires cable separation in accordance with the Exceptions.
Some thoughts from this forum??

WARREN1,
I keep seeing that 2" rule pop up. The exceptions are certainly lengthly on this one..

Could you sleeve the under 600 v in a NM flex conduit?

And to effectivly separate I think they would have to be secured in place