BREAK IN A CABLE.

New Zealand Herald, Volume LXVI, Issue 20365, 20 September 1929, Page 14

BREAK IN A CABLE.

ACCURACY IN LOCATION.

FAULTs,NEAR NORFOLK ISLANE)

IRIS BACK FROM REPAIR TASK.

The Pacific Cable Board's steamer Iris returned to Auckland yesterday after locating n break in the Sydney-Suva cable within a few hundred yards of the point estimated betore tho vessel left her moorings at Devonport seven days previously. Tho remarkable precision of tho instruments used in fault-finding narrows the dragging of tho sea bottom down to <1 very small area, am] on this occasion the defective section was picked up about four miles from Norfolk Island.

A heavy swoll prevented an immediate start when tho Iris arrived in thhe vicinity of the fault, and tho vessel spent o day at Norfolk Island, starting out to pick up the "cable at daybreak on Monday morning. At the first drag the cable broke after a short length had been retrieved, and three other breaks occurred before the affected section was all in hand. The work was finished 1 shortly after midnight on Monday, a three-miles length of new cable boing introduced into tho line.

Tho location of such defects is effected by delicate measuring of the resistance of tho conductor between two stations. In this case the checks woro made between Norfolk Island and Suva, and the difference in the" electrical resistance at tho two points provided data from whicn the defective point was found. The small currents on which these cables are operated can be appreciated in comparison with tho ordinary electric lamp used for house lighting. Tho houso lamp usos many times more current than passes through an ocean cable, and the experts work with currents which seem absurd in a conductor spanning hundreds of miles of ocean.

Near Norfolk Island very heavy armoured cable is used. Tho section just replaced weighs 26 tons to the mile, while deep-sea cable weighs as low ■ as two tons a mile. Tho shallow water off Norfolk Island and the combination of a coral and shell bottom and frequent swells destructive to . tho strongest cable. The portion removed had been in position for 14 years, and the sheathing wires showed evidences of prolonged corrosion-and chafing. In several places steel armouring, ~ four-tenths of an inch in dipnieter, had been worn away until little protection remained.