I'm going to run a ghetto power drop into my 'workshop' from a dedicated 15Amp outlet elsewhere in the house. I've got a heavy-duty extension cord I'm going to route through the attic, but where it dangles down from the ceiling I'd like it to look as neat as possible. To keep things organized I blended up this cable clip.

I thickened the connection in the 90 degree bend for strength. The mounting holes are designed for standard drywall screws and are counter-sunk.

The stl file has eight brackets on one plate. I had curling issues, so I had to print them on a raft.

The blend has the model before applying the modifiers, rotating to printable orientation, or arraying.

For slightly smaller diameter cable you can just thicken the wall to the inside. For significantly larger/smaller diameters you would need to recreate the inner portion.

There is a similar thing that would be useful for lighter cabling: http://www.thingiverse.com/thing:4752