I read a previous post here referring to SEU cable, and due to its construction, it could be run indoors to the load panel without using conduit. I need to install a sub panel for my air compressor and welder. The sub panel will be in the attached garage, and the total distance between the main and sub is about 12 feet. I could run conduit, though it would be much easier to run a flexible line. So—QUESTION ---Could this cable be used to connect a sub panel to the main breaker panel?

If I use conduit a short section will have to run along the outside wall. Question - I assume that ridged tubing will be needed? PVC is not allowed here as far as I know, haven't checked with code.

Depending on which I use, what is the proper grounding method? Obviously, there will be two hot and one neutral feed wire. If SEU, will I use a bare ground cable to ground the sub to the main? If conduit, will that suffice to ground the sub with the main, or still need a separate ground? The house is 40 years old, and the main panel has the two hot feeds and the neutral, the latter connected to the neutral bus. The system is grounded via a wire/conduit/ground strap combo that is connected to the meter box at one end and a ground rod at the other. The main panel is grounded to the meter box via the ridged conduit.

I don't know what amperage panel you plan on installing in your garage but there are several things to consider. SEU cable can be purchased with 4 conductors, 2 hot conductors, 1 neutral and a separate one for the ground. Code usually requires that the neutral and ground be separate and not connected at the subpanel. Conduit normally wouldn't be required unless it will be exposed to some kind of dangerous condition such as vehicles hitting it.