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No, all phase conductors are required to be in the same conduit. Failure to do so can cause heating between the conduit and failure of the conductors or equipment. This phenomenon is called hysteresis. Technically, if all conduit & fittings and discon next is plastic or fiberglass, and the conduit does not pass thru metal such as a metal wall, you can group the phases if you want. Otherwise it is a code violation. Please let me know if you have any more questions. Thank you Ken