To protect cathodically a remote gas well casing or pipeline, it is often necessary to erect miles of high voltage power lines to the site. The high voltage a.c. power must then be reduced and rectified to supply a trickle of d.c. current to a groundbed. Practically, the protection thus supplied to a pipeline or well casing is well worth the effort. Economically, however, it is akin to laying miles of pipeline to supply gas for a stove in a lone dwelling.