Overhead Electrolysis and Porcelain Strain Insulators

There is a slight leakage of current from trolley wires to earth through insulated supports on all electrical overhead construction, which if not checked permits a flow of current which gives rise to electrical separation of water into oxygen and hydrogen. The oxygen liberated acts vigorously upon the adjacent metal parts, which in time become badly corroded. This electrolytic action also seems to remove the galvanizing from live metal parts before attacking the iron. A partial remedy for this rusting of live galvanized wire is painting. This electrolytic effect is also seen to take place over strain insulators where the creepage distance is insufficient. This indicates that a creepage distance proportional to the conditions met must be secured to stop the flow of current around the outside of the insulators. The author concludes that, under fog conditions, the insulator surface exposed for creepage is insufficient in our present standard devices. Another form of overhead electrolytic action noticed in electric railway work is caused by use of dissimilar metals in contact. Sulphuric acid and other fumes in the air, and ozone from a nearby ocean, are supposed to be the electrolytes that set up a local battery action at these points of contact. The logical remedy for this trouble is to use similar metal in contact. The paper then describes the troubles encountered in San Francisco due to these causes and the remedies which have been applied.