MAIN MANGAHAO TRANSMISSION LINE.

Shannon News, 9 March 1923, Page 3

MAIN MANGAHAO TRANSMISSION LINE.

CONSTRUCTION GANG PAST LEVIN. SOME SUBSTANTIAL POLES. To .the average, person outside the town of Shannon, despite reports of progress at Mangahao, the formation of Power Boards and the raising of loans, the coming of the electric power to the district has, hitherto, been an indefinite thing—something belonging to the hazy future. Very concrete evidence of its approaching reality, however, is now given in the double line, of huge poles which stretch southward in an unbroken line from Mangahao to Kimberley Road, just below Levin. These poles, when the chain is completed, will bear the main transmission cables from Mangahao to Wellington, and will eventually carry 12,000 horsepower of potential energy from the giant turbines at Shannon to the mills; iactories and homes of the Empire City. f .. . AN IMPRESSIVE SIGHT.

■Fifteen inches in thickness at the ground-level, and tapering to nine inches at the top, .with double poles at intervals where added strength is required, this line of 44ft sticks with their 12ft cross-arms makes an -impressive spectacle, and gives some indication of the magnitude of the undertaking as a whole; • Taking no acecount of obstacles, of which, as a fact, after the first few miles, there are none of a serious nature, the line takes the shortest possible route for Paekakariki, which is to -be the ,end .of . the present contract—a total distance of 42 miles.

From Kimberley Road, looking towards Shannon, the view of the work is particularly impressive. From, here the line runs absolutely straight for over a mile to the back boundary of Mr Adkin’s property on Queen Street, and seen from this' point the towering ■ line of poles, five and a-half chains apart, but pn account of their height looking much less, stretch av/ay and gradually appear to come in the distance. A DOUBLE LINE. «Awisifr to the.’cbinstrUCtlon; camp on /Pararua Road by. a News repre : sentative. elicited spme facts, which will enable the man in the street tp form an ideal of the' amount of work involved in the. construction" of the dine.; As has been mentioned, the line ids a double ode—in reality two lines side by side, and 50ft apart, each'Of which will carry four cables, each cable consisting of 19 strands of 13 gauge copper wire, which will b e bare, that is, not insulated, special precautions being taken to prevent any* danger from leakage of current. The poles are of Australian hardwood, 56ft in length over all, each weighing approximately, with crossarms, 35cwt ? and are sunk in the ground to' a depth of eight feet, a portable derrick fiied to a lorry be.used'for; the. purpose of raising ihemito an upright; position. ' Twq ctoss-arms of 6 by 4in hardwood, eac| i’lff long for the drdinary pole, one a” foot from the top and the second nine feet lower, are affixed to carry the" cables. These arms are attached by means of a “U” bolt of one-inch iron passing round the pole and bolted through the, arm. Climbing steps lor the convenience of those who are to sling the cables and for repaii* 1 gangs later are affixed to every pole; " SAFETY FIRST. At angles, wherever the line crosses r a road, and it is necessary to elimiiiate air danger to (traffic through possible breakages, and at other places where it is considered necessary on account of strain; double poles are' erected. These consist of ttyo "ordinary- poles; bolted together ; .at; intervals of-‘five; feet with one-inch iroh bolts. .The cross-arms here are 13ft- 6in in length, and are one on each side "Of the pole, checked, or countersunk, and kept rigid by four 6 by 4 by Bin blocks between, bolted through with one-inch bolts, the whole braced with four cross-arm stays of 2 by £in iron 3ft 7iU long. These double poles are bedded in concrete, the whole depth of the hole, and to a width of ; 2ft 6in, as are. the single poles whenever, on account of the nature of the ground, it is considered necessary. :In addition to this every angle post is guyed with steel rope from below the lower cross-arm to a position 20ft from the base, and attached to 10ft hardwood posts sunk six feet in the ground. The holes for these double poles are an 'undertaking in. themselves. On the. surf ace they measure 12ft by 2£ft, and are sloped gradually in from one side, to within 3ft of the bottom, to facilitate the sliding in of .the pole.

THREE AND A-HALF TON POLES. As may be imagined, the erection of these, huge double poles, weighing, as they do, three and a-half tons, is a considerable item. By means of the crane, the pole is first got into position over the hole; a concave iron plate is placed on the inside of the hole to prevent the butt from digging into the side as it is being erected, and everything being ready, a threequarter inch steel derrick cable is fastened to the pole below the crossarms, and the first lift of 16ft is taken. Pike-poles, which are 18ft long, four inches in thickness, and fitted with four-inch spikes at each end, are fixed in position ,to take the weight, nine being used for the purpose. The crane is then shifted to a position immediately in the rear of the pole, at a distance of about 40 yards; guy ropes are attached to each side of the pole and to the front, to prevent it swinging to one side or the other, or going past the perpendicular, and the final lift is commenced. Four men work the crane, two are in charge of the side guy ropes, and the foreman with a jack to guide the butt into position as the pole rises, directs the operation. The erection of one of these double poles takes on an average three-quarters of an hour. This, however, is only the first part of the job, as the, whole has now to be concreted, the completed operation taking about four hours. Five bags of cement are used to each hole.

The erection of the single pole is a

comparatively simpler job, the usual time for erecting and filling the hole —where it is not necessary to con-crete-being three-quarters of an hour. It would 6eem to the layman that these double poles, sunk in concrete as -they are, should be capable of standing any strain that could possibly be -imposed on them. Such, however, would not appear to be the opinion of the engineers, for at certain places, the banks of the Ohau being amongst them, what are known as \‘H” poles are erected. These consist of two poles set five feet apart, braced with horizontal wooden struts. Between these struts, double diagonal cross-bars of iron verying from one inch to one and a-quarter inches are bolted, through the poles, forming the whole into a rigid mass. The crossarms on these “H” poles, double and braced as in the “double” pole, are 17ft 6in in length.

RIGHT-OF-WAY THROUGH PROPERTIES. Along the route, whenever it is necessary to cross a fence, either from a road or at a sub-division, a gate has been put in, with strainers of hardwood, the one on which the gate is swung being bedded in concrete. This makes a complete thoroughfare along the whole length of the line to facilitate repairs, etc. Wherever necessary, side-cuttings, fillings and so forth are. being made. THE ROUTE. The line, which crosses the Ohau River about three-quarters of a mile above the Muhunoa bridge, will cut through the valley at the back of the hills facing Manakau into the Manakau Valley, and will pass within three and a-half miles of Otaki. Work was begun in the second week of November, and, unless unfavourable weather supervenes, it is expected to complete the erection of the poles as far as Paekakariki by the middle of August, eleven miles being done up to date. From Paekakariki to Wellington it is possible that, owing to the difficult nature of the coun-. try, steel towers will be erected to ca'rry the cables from crest to crest of the hills.

So far it has not been definitely decided when -work on the slinging of the cables will commence.

Twenty men, under a Government supervisor, are engaged on the job, which is being put through by the firm of P. R, Baillie, electrical construction engineers, of Wellington. Mr A. P. Pulley is construction foreman. The best day’s work up to date has been three-quarters of a mile, which, considering the amount of work involved, appears to be very Satisfactory even for a ten-hour day. ; ;