ELECTRIC SHOCKS

Greymouth Evening Star, 9 April 1932, Page 10

ELECTRIC SHOCKS

SYDNEY BRIDGE TOLLMEN.

SYDNEY, March 31.

An interesting discovery since the opening of the Sydney Harbour Bridge, [though one that has been disturbing for the men concerned, is that at certain times and in certain circumstances, toll collectors have received fairly severe electrip shocks as they gathered in the revenue from car drivers. Though experts have examined the position since the nrst complaint was made, they have been unable- to offer any certain explanation, and the position is intriguing students of the vagaries of electricity. Not only the collectors, but many motorists have received shocks when the money was changing hands. The shock is felt when the tollkeeper first touches the proffered coin. Nothing is felt on; subsequent contact. In one or two instances, where the car was one of high engine revolutions, the shock has been so severe that the collector lost control of his fingers temporarily. "At first the shocks were attributed to a leakage from the electric light standards to the iron railings of the stands on which the tollkeepers work —there are six of, them employed constantly. This was disproved when the men stood clear of the roadway. Perhaps the most likely explanation is that offered by Mr. James Nangle, of Sydney Observatory, who suggested that the cars may receive a charge by passing through the electric field created by so many high tension wires and other electrical devices with which thd bridge is loaded. Another su'ggestioan is that the shock comes from the static induction of the cars.

Dr. Bradfield, after an inspection and experiment, offered the explanation foat the cars, in making an uninterrupted run up to the toll barriers, were charged with an escape of current from the storage batteries. This charge, remaining in the body of the car and in the driver, who was in direct contact with its mechanism, followed its natural course and escape.d to the toll collector,'as soon as he made contact either with the body of the car or the driver.

Uniyersity authorities explain that friction with the' ; air, particularly when it is dry, generates electricity in certain circumstances, and that this would bd stored in' the metal of the- car, since the rubber tyres form an insulator ’ - So far none of the collectors has suffered any ill-effect, and most of them are becoming gradually immune. Never at any time has the effect of the shock travelled further than the elbow.

EXPERTS’ EXPLANATION. The explanation given by experts is reassuring. ’ Dr. J. J. C. Bradfield described as “quite a simple matter” the source of the shocks of electric currents which are. being-experienced by toll collectors and motorists. ‘He explains that the source of the shocks,' far from being unaccountable, constitutes one of the .simplest principles of electricity, and that the position will be remedied by placing rubber pads on the toll collectors’ stands. The use by the collectors of boots with crepe rubber soles, he points out, would also meet the position. It is explained by Dr. Bradfield that, in the comparatively long run to the toll barriers on asphalt, and with the battery of a car generating electricity all the time, the vehicle itself, as well as the passengers, receives some of the current in common with the battery. The drier and hotter it is on an asphalt road the more electricity one gets into his car. Thus, on a toll collector making contact with this stored energy, through the medium of the car or the hand of the driver, there is a slight discharge of electrical current by its passing from the one person to the other.

“If the person collecting the toll stands on a piece of rubber no shock will be felt,” Dr. Bradfield adds. " Another prominent engineer thus describes the position:—A car in rushing through the air picks up electrical charges caused by well-known phenomena. These charges ' are ' held insulated from earth on account of the rubber tyres fitted' to the car. While th© car is in a charged state any conductor of electricity, such as a man’s body, when brought near the charged car, will cause the car to discharge some of its electricity into the conductor, be it a man’s body or something else, and thus will equalise the charge between the car and the man’s body. If the man is standing On an “earth” the car will completely discharge the electricity through his body. If ho is not standing on an “earth” it will only partially discharge. If, as suggested to counteract the shocks being experienced at the toll barriers, the collectors stand on rubber all the time, the- difficulty might be overcome.