SHOCKS ON BRIDGE

Evening Star, Issue 21080, 18 April 1932, Page 3

SHOCKS ON BRIDGE

PHENOMENA IN SYDNEY MOTORISTS’ EXPERIENCE. The phenomena of slight electric shocks reported by motorists and toll collectors on the Sydney Harbour bridge caused some discussion last week. Some car drivers, having experienced a mild charge of electricity at the moment they handed the toll to the collectors, expressed the fear that the bridge itself is charged. The explanation given by experts is reassuring. i)r J. J. C. Bradfield, chief New South Wales engineer in charge of the construction of the bridge, describes as “ quite a simple matter ” the source of the shocks of electric currents which are being experienced by toll collectors and motorists. Ho explains that the source of tho 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 tho position.

It is explained by Dr Bradfield that in the comparatively long run to the toll barriers on asphalt, and with the battery of the car generating electricityall 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 passage from one person to the other. “If the person collecting the toll stands on a piece of rubber no shock will bo 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 These charges are held insulated from earth on account of the rubber tyres fitted to the car. While the 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 tho electricity through his body. If he is not standing on an 1 earth ’ it will only partially discharge. If, as is suggested to counteract the shocks being experienced at the toll barriers, the collectors stand on rubber all the time the difficulty might be overcome.”