Cathodic protection

A cathodic protection system for a metal substrate has an anode which is normally electrically insulated from the substrate but which is disposed very close to the substrate. Cathodic protection only becomes effective when the electrical insulation breaks down and the metal substrate would otherwise be subject to corrosion. The system comprises an electrically insulating coating on the metal substrate and an electrically conducting coating applied over the insulating coating, a D.C. voltage being applied between the metal substrate and the conductive coating. The conductive coating or the insulating coating or both may be paint, the conductive layer being rendered conductive by the incorporation of an electrically conductive material such as elemental carbon.