EARTHING OF FENCES

Taranaki Daily News, 19 January 1935, Page 7

EARTHING OF FENCES

NO GUARANTEE OF SAFETY

GUARD AGAINST ELECTROCUTION.

ADVICE GIVEN TO POWER BOARD.

NO ACTION BY AUTHORITIES.

The North Taranaki Farmers’ Union recently made overtures to the Taranaki Power Board suggesting that where power lines crossed over fences they should be earthed to minimise the risk of electrocution to stock or persons coming into contact with a “live” fence. The power board on expert advice yesterday decided to take no action. Mr. H. B. Goldsmith, the power board engineer, reported that he had looked into the question of earthing fences in the Clifton area and felt that he could not advocate such a proceeding. “If all cross fences are earthed,” he stated, “and fences parallel with the line earthed at each quarter mile about 320 sets of earthing gear would be required. The total cost of material and labour, excluding transport, I estimated at £256. I do not consider the earthing of fences a very wise step as it leads to a false sense of security in the minds of the occupiers of properties so dealt with. Unless the connection to. earth is very good indeed and is maintained in this condition, then definitely the fence will remain alive when a low-tension wire falls on it. If a high-tension wire falls on a fence this will cause operation of the earth leakage equipment, whether the fence is intentionally earthed oi not. This, of course, leads to disconnection of the supply. “In the regulations it is clearly laid down that all earth leads and earth connections shall be tested at least every 12 months. It appears probable, therefore, that if fences are earthed by the supply author! ty the duty of maintaining and tesing these earths may alto fall on the authority. This would, of course, very greatly increase the cost of testing and maintaining earths in the district.”

The same question had recently come before the Wanganui-Rangitikei Power Board, said the chairman, Mr. H. G. Carman, who quoted a report made by Mr. H. Webb, the resident engineer. Tills was also to the effect that the earthing of a fence did not necessarily mean that it could be handled with safety if a live power line was in contact with the wire of the fence. DIFFICULTY IN PRACTICE. “It may seem a very simple matter to earth a fence,” said Mr. Webb’s report, “the general impression being that it is only necessary to drive a piece of iron into the ground and connect it to the wire. Many crossings have been Earthed by means of ordinary iron fencing stand? ards. In actual practice in New Zealand soil it is very difficult to obtain a reliable earth, and in some districts alfnost impossible. Where the country is dry, sandy or shingly good earths are very costly to procure end “The value of an earth as a means of protection is determined by its resistance to the flow of current to the ground. The standard maximum resistance of an earth as provided by the Public Works Department regulations is 10 ohms, which at 230 volte pressure would pass a 23 amp current, just about sufficient to blow most service fuses. “Where a fence is connected to an earth with a resistance flf less than 10 ohms and a live wire comes into contact with a fence wire the service fuse would blow and the fence remain safe to handle, but if the resistance is much above 10 ohms the fuses will not blow and the fence remains alive' at a pressure of 230 volts above ground and thus becomes a serious menace to man and beast.

“If a fence is not earthed it is highly probable that the top wife only will be livened up, especially in dry weather, whereas if the fence is connected to an inferior earth all wires are connected. together and in the event of a live line contact all wires in the fence become dangerous to stock. “Although an efficient earthed fence may be quite safe to handle when a live wire has contacted with it, a fence which has been indifferently earthed may be more dangerous than an unearthed one under similar conditions and it is the fear of creating a false sense of security that has prevented the board from recommending the earthing of fences by farmers.”

The chairman advised that no further action be taken in view of what the fWo engineers said. Mr. Knuckey agreed that no further action should be taken and he pointed; out that the work would entail great ex? pense. He would be only too pleased to see the work done if it were possible. It was decided to take no further action in the matter.