I am in the process of running an underground electrical service from my house to my workshop. I plan on running 220v 75A service using #3 Awg copper direct buried cable. The distance between my house and the workshop is 150' but Im not sure if I need to use conduit.
I would use conduit with individual thwn wire. Dig it once and you can always change the wire down the road if need be. Don't forget you need 4 wires H H N G and keep the neutrals and grounds seperate in the panel in the workshop and you need ground rods.