I've check 230, 300 in NEC and I can't find where it states: you need to place divider in a pullbox to seperate services of normal power leaving 2 switchboards routed into the same pull box.
You won't find it for your scenario. If you were talking devices with over 300 volts between them in a common box, or emergency systems and normal systems (see articles 517 and/or 700) there would be requirements.