This is my primary setup. There are 12 turns of 3/8" soft copper tubing spaced 1/2" apart. I used 1" x 6" square PVC pipe to hold the primary in place. Notice the heavy black cable connected to the primary via an aluminum clamp. This seems to work with little heating so I would say the power is being transferred efficiently. I used to use a copper clamp then I tried a steel clamp but both clamps would heat up to the point that you could not touch them. The primary sits 4" below the secondary.