Publication: The Electrician & Electrical Engineer
New York, NY, United States
THE CONSTRUCTION OF LINES FOR ELECTRIC CIRCUITS.
BY THOMAS D. LOCKWOOD.
THE clothes-pin attachment, like most great conceptions, is exposed to the fate of being Hon. Amos Kendall, the early agent of Morse, was, before 1850, delivered of the following remarkable system of insulation which we give in his own words: "I think the following the cheapest mode of insulation vet devised, and as effectual as any: With a wide set saw, or Otherwise, make a gap in the post downwards, at all angle of 45░, wide enough to receive the wire with its covering. Just cover the wire with the best india-rubber cloth, or a composition of which india-rubber is the chief ingredient, so far that the covering shall extend about 2 inches from the post on each side. Over that, wrap sheet-lead or tinfoil, not, however, extending more than an inch on each side of the post. Sink the wire so covered into the gap on the post, then pass large twine turned around the lead covering on each side of the post, and tie it tight round the side of the post opposite to the gap. It will have the double effect of confining the lead and turning off the water." Happily for the memory of Mr. Kendall he never tried this alleged insulator.
Another brilliant idea is embodied in the "picture" below. It was first introduced into civilized society by an article in the New York Electrical Review, based upon a letter from Aguascalientes, Mexico, which states that the Zacatecas state telegraph lines use these apologies almost exclusively. The attachment itself, as clearly shown in the figure, is a piece of horn, with tip and butt sawn off, and a notch cut in the top. It is, of course, hollow, and surrounds the top of the bracket to which it is screwed. The line wire is passed through the notch and held there, by being fastened with a piece of No. 14 wire. The letter describing this remarkable appliance na´vely states that "these horn insulators, although poor insulators for telegraph, are splendid anti-induction insulators for telephonic use." This statement lets the cat out of the bag. The horn insulators are poor for telegraphic purposes, because they are not insulators at all. Horn is not very much of an insulator at best, having about the same specific resistance as the hard skin of the hand of a laborer, and whatever insulation it possesses is lost by the method of fastening the wire. It is because of this non-insulating character that it will answer in a dry country for telephonic purposes, affording just sufficient leakage to keep the line clear of static induction. It is, however, probable that if the horn was dispensed with altogether, and the wire fastened directly to the bracket or pin, it would work just as well in dry weather. In wet weather, it is not likely that either wood or horn would prove eminently satisfactory, even for telephonic service.
It is a pleasure to look away from these oddities, to an invention in insulators which possesses real merit, and which, when better known, will be extensively employed. I refer to the form of insulator shown in figure 7.
A glance will show the nature of the improvement. In addition to the regular internal screw thread with which the insulator is as usual attached to the pin, there is an external screw on the apex of the insulator, but oppositely wound. That is, if the internal screw is right-handed, the external one is left-handed and vice verse.
The line-wire instead of being bound to the insulator with a tie-wire, is fastened with a special clip which is shown detached, in figure 8.
The object in providing the right and left-handed screws, is so that the wire can be fastened to the insulator, and the insulator screwed down on the pin by one and the same operation.
In attaching the wire, the insulator is placed on the pin and given a couple of turns down. The clip is hooked on the line-wire with the ends of the hooks turned upwards. The loop thus formed is then slipped over the top of the insulator, and (care being taken to see that the clip goes down the thread of the screw first with the line-wire following) the insulator grasped by the hand, is screwed clown on the pin as far as it will go, the outside screw at the same time insinuating itself into the loop of the line-wire and clip. These instructions for attachment, are by no means intended to serve as ironclad rules to be observed, but an intelligent lineman observing the intention of the improvement, will readily adapt himself to it, and act according to the different conditions of each case. Even if insulators of this character are employed, circumstances may of course arise in which it will be found desirable to use the old mode of attachment. The insulator as now made, is provided with the ordinary circular groove, upon which the line-wire rests, for attachment with the old time tie-wire.
It is, perhaps, unnecessary to recapitulate the advantages which are secured by the use of this form. It is well-known that a concomitant trouble of the old form of attachment was that scales of the zinc coating were sure to be rubbed off, thus leaving spots of unprotected iron wire at which oxidation would promptly commence. The leakage at each insulator may also be reasonably expected to suffer diminution, as the points of contact are lessened; while the line-wire suffers much less mechanical strain. It is also claimed that much time is saved in construction by its use, and it is evident that a single clip may be used many times, and that if it becomes necessary to detach the line-wire at any time, a few backward turns of the screw is the only operation necessary. Practical linemen whose opinion I have asked on this subject, concur in praising it highly and advocate its use, and it would therefore seem that one of the greatest obstructions which threaten innovations, e., the opposition of workmen, will not retard the introduction of this insulator.
The application of the external or wire attaching screw, is the invention of an Englishman, J. Slater Lewis, and has been patented, in the United States. The happy conception of forming the outside screw of opposite direction to the internal or pin screw, so as to provide for the simultaneous attachment of both line-wire and insulator is, however, to be credited to Frank L: Pope, and is fully described in a patent issued to that gentleman, December 25th, 1883. Both patents have, for the entire country, passed into the hands of the National Insulator Company, of which Messrs. Loren N. Downs and II. B. Lytle, of Boston, are respectively President and General Manager, and J.W. Duxbury, of Providence, R. I., Treasurer. These gentlemen recognizing the practical merit of the combination, and having, moreover, control of other improvements in insulators, have