THE MOLE PLOUGH

Grey River Argus, 15 December 1937, Page 3

THE MOLE PLOUGH

Engineers Use Old Device POST OFFICE CABLE LAYING, The New Zealand Post Office has adapted a very ancient agricultural device for a modern purpose, in using tne principle oi tne mole drainage plougn Lor laying lead sheathed teiegrapn and teiepnone cables. Where tne soil is suiliciently compact, farmers are able to drain it by using a plough carrying a narrow vertical blade to which is attached at the bottom a torpedo-shaped mole. When this is drawn forward, the mole, plough, instead of raising a furrow, drops beneath the surface to a predetermined depth, and opens up a circular drainage channel. With tne increasing use of the sheathed cables carrying many scores ot wires insulated with paper, the Post Office has done much to reduce the overhead aerials which are so prominent a feature of the country landscape. The engineers’ adaption of the mole drainage plough enables cables to be efficiently and quickly laid in the ground, although this process is not possible in city streets. For cable-laying, the plough is drawn by a tractor, and the cable follows the mole into the neat tube-shaped channel which it makes, usually about eighteen inches below the surface. A length of 120 yards is laid in one operation, and a further 120 yards is uncoiled from the cable drum and buried by the plough before it is necessary to cut the cable to resume laying. To avoid undue strains on the plough and cable during haulage, an ingenious mechanical fuse has been evolved. The tractor drive to the plough is carried by a wire having a definitely limited tensile strength, so that if the torpedo-shaped mole strikes an. obstruction, the “fuse” is broken and no damage is done excepting to an inexpensive piece of wire. There is another mechanical fuse in the device, this being the connection from the torpedo mole to the head of the cable which it drags beneath the surface. Any exceptional strain breaks the "fuse” before the pull approaches a dangerous load on the cable, so that it is saved from damage. This system of cable laying not only has the advantage of being faster, than trench digging, but also avoids disturbance of the soil.