We have been asked a few times in the recent past as to whether we can run DC and AC cables run in the same conduit.
The answer is No since the DC cables could induce a DC voltage onto the AC side. The AC sine wave should oscillate about the 0 volt axis i.e., the positive and negative cycles should be the same. If a DC voltage is induced into the AC sine wave, then the AC wave will no longer oscillate about the 0 volt axis (as shown below).
This is also specified in the South African standard SANS 10142-1 section 6.1.10 – “Conductors that form part of a d.c. installation shall not be run in the same wireway as conductors that form part of an a.c. installation.” The South African standard has been derived based on the British standard which is also what we follow here in India.
One can achieve isolation between AC & DC cables using trunking that has an internal divider to separate AC and DC cabling. This does not provide any EMI/noise protection between cables but does give suitable electrical isolation/separation. One must however plan the installation so that the AC and DC sides remain separated along the full route. See image below where there is a divider: