Alternating-current electrolysis

The development of the one-phase railway motor leads to the introduction of grounded alternating-current systems, in which the current is returned over the rail. With rail-return, necessarily more or less current strays through the ground, reaching gas and water pipes, lead cables, etc. When using direct current for railroading, lead cables, etc. are protected against electrolytic corrosion by connecting them to the negative terminal of the circuit, so that the stray current enters the cable from the ground, but does not leave it; that is, the cable is always at a negative potential against ground. With alternating currents this method of protection evidently is not feasible, since the potential difference constantly reverses.