HIGH-TENSION WIRES.

New Zealand Herald, Volume LXVII, Issue 20594, 19 June 1930, Page 14

HIGH-TENSION WIRES.

THE ELEMENT OF DANGER.

AUTOMATIC SAFETY DEVICE.

EXPLANATION BY EXPERT.

Questions concerning tho safety of highvoltage electric transmission wires were asked in a Compensation Court yesterday during tho hearing of a caso in which a largo sum was claimed from tho Public Works Department for alleged depreciation in tho valuo of a property at Panmure crossed by steel towers bringing power from Arapuni. Current, it was stated, passed through the wires at 110,000 volts.

A witness for the department, Mr. T. McLennan, district electrical engineer at Hamilton, stated in evidence that only one instance had been recorded of a wire breaking, and in that case the cause was a rillo bullet, which broke a wiro in the Wellington district. If a break occurred tho lino was instantly mado dead by means of an automatic device at Arapuni. Tho principle was that as long as the wires were intact tho current flowed smoothly, but once contact was made with tho ground, which would happen in tho caso of a broken wire, tho current leaked into the earth, and at that instant tho lino was mado dead.

Effect of Wiro Touching Pole

Mr. Justice Ostler: If a wiro broke and touched tho pole what would happen ? Witness said that as tho polo was connected with the earth the current would run down it.

Mr. Justico Ostler: And anyone who touched tho pole would receive a shock? Witness replied that the polo would be alive for only a very brief period. The earthing of the current would immediately set tho automatic device in operation, and the wires and polo would become dead. Mr. Leary, for tho claimant, asked witness why, if the precautions were so elaborate, it was necessary in the Waikatg district to issue instructions to schoolchildren warning them of tho danger of flying kites near the transmission lines as tho practice " may have fatal results." Mr. McLennan said the warning referred only to the ilying of kites. If the kito string touched a live wiro tho string would act as a conductor for the passago of the electricity from the wiro to tho ground, and the" lino would bo cut-out, and so rendered safe.

Mr. Leary: And what about tho boy who is kind enough to act as a buffer ? Mr. Justico Ostler said the question need not have been framed in that way, and witness did not answer. Crossed Wires Become Dead.

In reply to Mr. J. B. Paterson, assessor for the claimant, who asked what would happen if two wires accidentally crossed, witness said that both lines would bo made dead instantly by means of tho automatic device.

Mr. Paterson: And if a wire came down against a tower, ivould it make it alive? Witness: Only for the instant. Mr. Paterson: Then why do you put v>)> notices on the towers warning people that they aro dangerous? Witness: I take it that they are put there merely to prevent people climbing np the towers, as it would bo dangerous to do so. Strength of the Insulators.

Mr. Paterson asked what would happen if one of the insulators on the towers broke, and so caused tho wires to fall to the ground. Witness: Tho probability of the insulators breaking is extremely remote. Mr. Paterson: But we know they do. Witness: Not this typo. They are guaranteed by the makers. Should it happen, the current will go down tho tower to tho earth, and that will be sufficient to cut off the power instantaneously by means' of the automatic device. Mr. Leary quoted a case in which wires had come down and killed two bullocks without the line being made dead. Witness replied that that was duo to the wires not being heavy enough to break through the scrub and so reach tho ground. The wires from Arapuni, however, were much heavier, and would be certain to " ground " in the event of an insulator breaking. .