As long as he stays inside the home MN cable is acceptable as per 680.21(A()(4).
"In the interior of one-family dwellings, or in the interior of accessory buildings associated with a one-family dwelling, any of the wiring methods recognized in Chapter 3 of this Code shall be permitted that comply with the provisions of this paragraph. Where run in a raceway, the equipment grounding conductor shall be insulated. Where run in a cable assembly, the equipment grounding conductor shall be permitted to be uninsulated, but it shall be enclosed within the outer sheath of the cable assembly."
As soon as you leave the structure you would have to convert. This usually is not that difficult. This is how I interpret it. I have done it this way for awhile with no prolbems. At least not yet.
Blessings. Mark
