induction and magnetic effects and causes a heating effect in u201c skin effect u201d heating heat is generated in the ferromagnetic envelope wall by the i u02dc r loss of return current flow and by hysteresis and eddy currents induced by the alternating magnetic field around the insulated conductor the electromagnetic interaction between the current in the insulated core conductor and the return current in the envelope causes the current to concentrate at its inner surface due to skin effect hence the name skin effect heating cable the strength of this phenomenon is increased by being in close proximity to the core conductor referred to as proximity effect the proximity relation of the two conductors causing the current to flow out and back and proper electromagnetic shielding further increases these effects the basis of the present advantageous system alternating current flows only along a band of the skin of the elongated piece of ferromagnetic material acting as a very specialized conductor under these conditions as a non limiting example a ferromagnetic pipe may be considered which has a minimum wall thickness of about three times the skin depth or about u215b inch more or less for various ferromagnetic materials and ac frequency ac may be conducted out to the far end of the pipe by an adjacent internal and insulated wire which is connected to the inner wall of the distal end of the pipe due to what is called the u201c skin effect u201d a substantial portion of the ac flows back on that part of the inside surface or skin of the pipe which is immediately adjacent and parallel to the conductor wire this band of the steel surface subtended from the wire becomes what may be called a skin effect conductor resistor the balance of.