ELECTROLYSIS

Hokitika Guardian, 23 July 1930, Page 7

ELECTROLYSIS

' HAVOC UNDERGROUND .LECTURE BY TELEGRAPH ENGINEER. CHRISTCHURCH, July 21. “When it was discovered in Christchurch recently that electrolysis wa,s , playing havoc with the water mains, a i newspaper stated that some engineers, * who had been interviewed had said that electrolysis was practically unknown in the Dominion,” said Mr D. Parton, District Telegraph Engineer, when reading a paper be ore the Canterbury College Engineering Society on j Saturday evening. His subject was | electrolytic action on underground metal structures, such as water and gas I mains, and telephone cables. J What was called “electrolysis,” cotij tinned Mr Parton, was the chemical decomposition of a substance, brought about by tbe passage of an electric current through it. The statement referred to was made in ignorance of the true position, for there was in Christchurch evidence of such chemical decomposition. If the trouble had not been brought to notice, it was not j because it was absent, but because preventive measures had been taken. Corrosion had most certainly affected the ; underground networks, both here and in other cities, but invariably the cause of corrosion had been attributed to but e'ectrolytic action. In Auckland the most serious cases had occurred, and in A ustralia it was found 1 not only that the water mains and telegraph cables attacked, but also that the reinforcing stool .of ferroconcrete buildings had suffered. Mr Parton showed how the currents producing electrolysis were set up. The most common method of tramway electrification was the single trolley wire system—isucli as that obtaining locally—in which the overhead cable acted as one of the two electrical conductors, the second conductor being the metal rails. Current from the power station passed from the overhead wire to the motors of the tram, then into the rails and so back to the station. It was from the rails that current leaked. Whilst most, of the current would normally be carried by the rails, if any conductor nearby offered less resistance, much of the current would pass through the ground to this conductor, by which it would then be carried. At some point it would return to the rail. It was at this point that trouble would be expected, for the passage of current from the metal through the ground tended to dissolve the metal, in much the same manner as the process of electroplating.

In the case of underground telephone cables, the lead covering would be pierced, the wires exposed to tbe damp and the cable rendered useless. Such action had not yet seriously affected the system in Christchurch, ‘but pitting had taken place to a limited extent. Excessive leakage of tramway current was known to exist in certain areas, such a,s Cashmere, Upper Riccarton and Ferry Road, but- it had been detected and measured periodically and prevented from doing any damage Any structure more than four feet below or to the flank of a rail was little affected, but in many cases structures were within the regulation distance of two feet six inches from the rail. After a discussion on ,liis paper Mr Parton was accorded a hearty vote of thanks