Publication: The Electrician & Electrical Engineer
New York, NY, United States
THE CONSTRUCTION OF LINES FOR ELECTRIC
BY THOMAS D. LOCKWOOD.
(Continued from page 89.)
WHILE the use of iron for tins purpose is by no means extensive, it is constantly increasing in favor, and will probably become very common in countries where wood is scarce, or where it rapidly decays. Its use is to be commended, even in this country, for lines which pass through parks or private grounds, or through handsome streets where the ordinary wooden pole would be objected to by municipal authorities or property owners, as it is capable of being constructed in many ornamental and symmetrical forms. Of course the cost of an iron pole is much greater, but as a general thing it is more economical in the end to pay a little extra in this way, than to offend the sensibilities of the abutters. If poles formed completely of iron cannot conveniently be procured, a compromise may sometimes be made, by planting a stout cast iron socket, placing therein a strong shaft of timber, to give the desired length, and surmounting this shaft again by an iron top piece, carrying the iron cross-arms. The top piece cross-arms, and insulator pins may be made of gas pipe; or the crossarms may simply be short iron bars bolted to the pole, to which may be attached either pins or brackets.
Railroad officials or amateurs connected with railroads, will find that old rails make very good poles, as does also gas pipe; the latter especially when but a single line is required. Several forms of iron poles are already in use in foreign countries: In Switzerland for example, an iron pole consisting of a conical wrought iron tube is used; its length varies from 11 to 8 1/2 feet, its diameter at the base is about 2 3/4 inches, and at the small end about l 1/2 inches. These poles are set in foundation blocks of stone, the size of which depends on the size of pole which it is to support.
The iron post of W. Siemens is perhaps more extensively used than any other. It is formed in fishing-rod style of two tubes telescoping into one another, the upper one being usually surmounted by a lightning discharging point, while the lower end is secured by four bolts to a buckled iron plate bent or pressed into a dish-shaped form by which great strength is given to it. For a line of not more than three or four wires they form a very elegant support, and are made in sizes varying from 20 to 24 feet long, the average weight being about 185 pounds.
Lieut. James A. Swift in his book "The Practical Telegrapher" describes a very simple iron pole used by the U. S. Signal Service for single wire coast lines. It is of good iron, 20 feet long in the full; is tubular, having an external diameter of 2 1/4 inches, and weighs without the attachments about 75 pounds. The pin carrying the insulator is round like an ordinary cross-arm pin, and is fitted in the top of the pole. The most ingenious thing about the pole to my mind, is the arrangement provided for climbing. A hole is made through the tube from side to side about four feet from the top, and in this hole an iron bar about 15 inches long and five-eighths of an inch thick is thrust. A narrow strip of wood some 10 feet long and two by four inches thick, has spikes driven into its sides as steps or foot irons, while two hooks at its upper end are adapted to hang on the cross-bar above. The lower end is prevented from swinging round, by a clamp which clasps the pole. This arrangement being light is easily carried round from pole to pole.
It may be stated here, before we part company with the subject of iron poles that they have an advantage over wooden ones, in that being metal they themselves serve as lightning and leakage conductors; while they also have a corresponding disadvantage, in that a wire accidentally slackened or freed from the insulator, and hanging loose, will almost certainly fall against the pole and thus form a dead ground, while with a wooden support, in fine weather, the line could be readily worked as well as before.
CROSS-ARMS AND BRACKETS.
If only one wire is to be carried, one of two attachments may be adopted.
The insulator may be fixed to a bracket, and the bracket spiked to the side of the pole a few inches below the top; or the insulator may be affixed to a pin which is driven in a hole at the top of the pole. When the latter mode is adopted, an iron ring smaller when cold than the top of the pole, should be heated to bright redness and then slipped over the small end to prevent it from splitting. The bracket plan is however preferable, as the insulator and pin when attached to the top of the pole, are apt to be lifted off, when the pole is planted in a hollow, and even on a level there is an upward tendency. Brackets are made of locust or oak, should be painted before attaching to the pole, and are spiked to the poles.
It is better if more than one wire is to be strung, to use cross-arms. These are best made of white pine — and are of four by five stock. They are planed and have their upper corners beveled. The length of a standard cross-arm for two wires is three feet; for four wires five feet six inches; and for six wires seven feet six inches. It is usual to make the distance between the insulators 22 inches from centre to centre; and more than six wires are rarely placed on one cross-arm. The sizes given are for regular telegraph work. For telephone lines the insulators are usually placed nearer together, and as many as 10 or 12 on the same arm.
A thing not always attended to in the United States, is the numbering of poles and wires. Every line of a mile in length, or over, should have its poles numbered and a record of such numbers ought to be kept by a suitable officer. The work of maintenance is thus made much easier, for the location of any trouble can be more clearly indicated. Each wire should also be numbered, and the system of numbering pins should be uniform, so that the bare mention of a pin by its number may at once indicate to the mind's eye its exact position.
Before attaching the cross-arms to the poles, spaces are cut for their reception — these spaces are technically called "gains."
They are cut of sufficient width to give a snug fit to the side of the cross-arm and may be nearly two inches deep from the front of the pole. Brackets and cross-arms should always if possible, be attached before the pole is set; and may be fastened with bolts and nuts, with or without the addition of lag screws or spikes. All screws, spikes or bolts used for this purpose should be greased before they are used, to prevent rust. Cross-arms should also be well painted before being attached to the pole.
It is a saving of both time and work to fit the cross-arm with its pins, and to screw on the insulators, before the pole is set up, yet the insulator should not be screwed down tight, but merely attached loosely; so that it can be screwed down when the wire is strung.
It should be a rule of the line constructor, never to run a housetop line if pole rights can be procured. A line run over housetops is absolutely at the mercy of the householder; is liable to be cut at any time; is by no means so strong as a pole line, and at any time an order to remove the fixtures may be expected.
Many telephone companies which built expensive housetop systems of lines when beginning business, have been compelled to completely rebuild, after paying immense sums as damages for alleged roof injuries, and poles are in all cases to be preferred. Yet housetop construction, to a greater or less degree, will probably be carried on for some years yet, and an article on construction would manifestly be incomplete without reference to it.
The fixtures employed to support roof lines, are of several kinds — but may, perhaps, be broadly divided into the two great classes, i.e., wall and roof fixtures. Both classes, again, may be either double or single, according to the number of wires which are to be supported. Roof fixtures are those which are placed with their foot on the roof — they are fastened to the roof by iron angle plates, which are fixed by screws, and are furthermore firmly braced by iron rods, in the direction of the wires on both sides.
Wall fixtures are spiked to a piece of plank about five feet long, 10 inches wide and two thick; the said plank being first spiked to the wall itself with seven inch spikes. These uprights are, or should be, five inches square and 20 feet long, 15 feet of which are elevated above the wall, the remaining five stretching over the baseplank. Such an upright may reasonably carry three cross-arms; the bottom one being 54 inches long; the middle one 33 inches, and the top one 18 inches long. The same thickness of upright may be used for double fixtures, but the cross-arms for these are, of course, extended across and supported by both uprights, which are braced together by wooden braces, crossing one another, so as to give stiffness to the structure.
All screws entering roofs should carefully be soldered over to prevent leakage.
Single fixtures may be used in all cases where there are not more than a dozen wires. All housetop fixtures, crossarms and boards ought to be of white pine, painted. In addition to these fixtures, some constructors use tripods, composed of three round iron rods welded together at the top, which is made to serve as the insulator pin. The use of these contrivances is not to be commended, unless they are made very high, inasmuch as wires run on them when low are apt to trip the unwary lineman precipitately into the street. Ridgepole irons and chimney irons are also sometimes used, and serve very well for the attachment of glass insulators, but on the whole, a wooden block, with a rubber-hook insulator is preferable for such work, especially if the wire is a light one, because in lieu of using a tie wire, the wire can be twisted round ihe hook, while where the block cannot be conveniently placed, a batten or counterbrace consisting of a three by four, or four by five-inch pine stick, spiked to the roof at one end, and projecting over, may be used. Without exception, housetop fixtures must be guyed against lateral strain.
Where a heavy line runs straight from fixture to fixture, it requires two guys to the fixture, one on each side, to stay it against the side pressure of the wind. When a line makes an angle with a fixture, the guy must be so arranged as to pull against the angular strain. Where the span on one side of a fixture is longer than that on the other, a guy is required on the short side to balance the surplus strain. It is customary to use No. 9 B. W. G. wire for housetop guys, although a pair of No. 12 wires will do quite as well.
When a line, short or long, is to be built, unless the person in charge of the construction well knows the two terminal points, and all available routes between them, the road should be carefully gone over, and a route laid out, before any work is done, and if any rights of way are necessary, they should be arranged, so that when the construction gang comes along, it will have nothing to do but its own work. If it is a long line, and the men have to rest in a different place every night, suitable places should be agreed for, where they may board in as comfortable a manner as possible.
The person who goes over the road, if a capable and practical constructor himself, can render material assistance to those that follow after, besides aiding to soften the acerbities which sometimes spring up between the pole owners and the pole abutters, when passing through towns and villages. A line of wire has, of course, more or less, to follow the windings of the road, but in many places there is waste land, likely to remain so for years, and such places, when treeless, may be availed of to shorten the curves. Some suitable mark to designate where poles arc to be planted is to be adopted, and while it is never well to be chary of poles where it is needful to set them pretty close together, it must not be forgotten that while multiplying the number of poles in a given distance does assuredly give greater mechanical permanence aud stability to the line, it at the same depreciates the insulation by multiplying the possible points of leakage. Here, therefore, is a great chance for good judgment, and a good line is one in which the happy mean is taken.
It may be thought immaterial which side of the road is taken, but as a matter of fact this needs as much care as any part of the business. There are many points which may guide one in this matter, and frequently the conditions leave one without any alternative. The amount of adjoining waste land on either side, or the number of trees or houses, all aid in determining this question. All things being equal, however, on a curved road, it is far better to set the poles round the inside of the curve; and this for two reasons — in the first place the line is thus shortened; and in the second place — as may be seen by the diagram, figure 9, the line is thus arranged with the strain off the road, so that if the wire in any way becomes freed from one or more of the poles, it tends to swing away from, instead of over the road.
(To be continued.)