Thermal insulation

“ If the insulation per mile, i.e., the total insulation multiplied by the mileage of the wire loop, is found to be less than 200,000 ohms, the wire is considered to be faulty. The climatic conditions in the British Islands are such that it is not possible to maintain, in unfavourable weather, a higher standard than that named, which is the insulation obtained when all the insulators are in perfect condition and only the normal leakage, due to moisture, is present. ”

“ These thermo-couples have shown that the temperature drop across the 2-in. air space was much less than that across the 1-in. layer of asbestos; 307 in fact, that it was considerably less than the temperature drop through the same thickness of the brick wall.
The results obtained prove that, as far as heat insulation is concerned, air spaces in furnace walls are undesirable. The heat is not conducted through the air, but leaps across the space by radiation. In furnace construction a solid wall is a better heat insulator than one of the same total thickness containing an air space. ”

“ Unless the insulation is perfect, the potential recorded falls short of that at the spot where the radium is placed or the water jet breaks. The action of the collector is opposed by the leakage through imperfect insulation, or natural dissipation, and this may introduce a fictitious element into the apparent annual or diurnal variation. The potentials that have to be dealt with are often hundreds and sometimes thousands of volts, and insulation troubles are more serious than is generally appreciated. ”

“ In pole and over-house lines, the wires are kept from each other and the current from escaping to the earth by insulators of glass. In Europe white porcelain and brown stoneware insulators are used, and the former substance, when of good quality, well glazed and well burned, is perhaps the most perfect of all insulating materials, and does not deteriorate with age. The fewer the poles on which the wires are suspended, the better is the insulation and the less the cost, but the liability to accident is greater. ”

“ The insulating joint may be omitted in conduit, armored cable, or metal molding systems with straight electric fixtures in which the insulation of conductors is the equivalent to insulation in other parts of the system, and provided that approved sockets, receptacles, or wireless clusters are used of a type having porcelain or equivalent insulation between live metal parts and outer metal shells, if any. ”

“ As insulating materials, whether rubber, cotton, or paper, may be impaired or destroyed by heat, it is necessary that the temperature of underground cables under full load be kept within safe limits. Rubber insulation can probably be raised to 125° or 150° Fahrenheit without injury, and paper and cotton may go a little higher. For a given size and make of leaded cable the rise of temperature in its conductors above that of the surrounding air, for a given loss in watts per foot of the cable, may be determined by computation or experiment. ”

“ You say the cooler is perfectly dry inside, therefore, its construction must be very good, but the outside insulation is not just right, so the outside becomes too cool and the moist air coming in contact with the cold surface readily condenses. If the cooler can be insulated in such a way that the outside will not become so cold, we have no doubt your trouble can be overcome. ”

“ It is one merit of the low-temperature work, I repeat, to have called attention to the possibilities of heat insulation in application to "the useful purposes of life." If Professor Dewar's vacuum vessel can reduce the heat-transmitting capacity of a vessel by almost ninety-seven per cent., why should not the same principle, in modified form, be applied to various household appliances—to ice-boxes, for example, and to cooking utensils, even to ovens and cook-stoves? ”

“ As it is easier for the current to circulate in a short path than in a long one, there is a continual tendency for it to jump from the overhead wire through the insulation to the ground, but this is effectually prevented by the very perfect character of the insulation. ”

“ In many animals the insulation is increased by non-conducting hair, wool, fur, etc. And naked man finds it expedient to reinforce his own insulation by clothing of silk, satin, hair, wool, flannel and other non-conducting materials. We are exhilarated by a dry atmosphere: depressed by a damp one, because the moist air, being a conductor, carries off some of our electricity to the earth, while dry air is a more complete insulator and prevents this leakage. ”

“ When the outside surface of an insulator is wet, as during a moderate rain, it seems that the under surface of the insulator, and the distance through air from the lower wet edge of the insulator to the pin or cross-arm, make up most of the insulation that prevents arcing over from the wire to the pin or cross-arm. It further appears that it is useless to extend the distance across the dry under surface of the insulator indefinitely without a corresponding increase of the direct distance through air from the lower wet edge of the insulator to the wood of cross-arm or pin. ”

“ A main conveying alternating currents of very high tension may be injured merely by a blow hole or small crack in the insulation, the more so as a blowhole is apt to contain gas at low pressure; and as it appears almost impossible to completely obviate such little imperfections, I am led to believe that in our future distribution of electrical energy by currents of very high tension, liquid insulation will be used. ”

“ Since no substance yet known is absolutely a non-conductor of electricity, perfect insulation is impossible. If, however, the supports on which a telegraph wire rests present, on each part and on the whole, so great a resistance to electric conduction as to allow only a small portion of the electricity sent in, in the actual working, at one end to escape by lateral conduction, instead of passing through the line and producing effect at the other end, the insulation is as good as need be for the mode of working adopted. ”

“ The ability to maintain a satisfactory temperature depends as much upon the construction of the house as upon the heating apparatus itself. Heat is readily lost through walls, roofs and windows. Most houses can be made more comfortable at small cost by applying insulation or by correcting defects in construction. ”

“ The wire to be wound on the bobbins is sold by all dealers in electrical apparatus. It is copper wire, covered with cotton or [Pg 68] with silk, to ensure insulation. Mention has already been made of what is meant by insulation at § 3, but, in order to refresh the reader's memory, Mr. G. Edwinson's words are quoted here. "To insulate, as understood by electricians, means to protect from leakage of the electric current, by interposing a bad conductor of electricity between two good conductors, thus insulating [11] or detaching them from electric contact." ”

“ Electrical inspection indicates that the winding is melted together in several places. You couldn't unwind the coil, let alone rewind it with fresh insulation. We've got a couple of gallons of insulation handy, if you get a good idea. ”

“ The art of insulating electric wires has been known almost as long as that of conducting electricity for practical purposes by means of wires. Prior to the use of electricity for lighting, however, the feeble character of the currents conveyed upon these wires did not require that the insulating material should be non-combustible, and the skill of the inventor was directed towards a method of insulation which should protect the wire from moisture and other external injury. ”

“ On land, where wires are carried on the tops of poles, the air itself is a sufficient insulator. A few glass rings at the points where the wire passes through the iron staples by which it is supported, and the insulation is complete. But in the sea the electricity would be instantly dissipated, unless some material could be found which should insulate a conductor sunk in water, as completely as if it were raised in air. But what could thus inclose the lightning, and keep it fast while flying from one continent to the other? ”

“ Motors operating at a potential of 550 volts or less must be thoroughly insulated from the ground wherever feasible. Wooden base frames used for this purpose, and wooden floors, which are depended upon for insulation where, for any reason, it is necessary to omit the base frames, must be kept filled to prevent absorption of moisture, and must be kept clean and dry. ”

“ To the passenger, the presence of the steel construction is apparent, but the insulation, which forms a vital factor in the car's construction, can be seen only during the process of building. Composed of a combination of cement, hair, and asbestos, this insulating material is packed into every cubic inch of space between the inner and outer shells of the roof and sides, forming a perfect non-conductor to protect the passengers against the biting cold of winter or the heat of summer sunshine. ”

“ Pipes may be insulated to prevent freezing, but this is not a completely dependable method. Insulation does not stop the loss of heat from the pipe—merely slows it down—and the water may freeze if it stands in the pipe long enough at below-freezing temperature. ”

“ In any other system we have the problem of splicing and cutting of cables, which, at its best, is bad work. What we desire is not such a high insulation as good mechanical protection. As long as we can hold a moderate insulation with good mechanical protection, that is all we want. ”

“ Insulation is the covering by which the escape of [8] electricity through the wire is made impossible. Always see to it that the insulation is in perfect condition.
All wires must be insulated. In damp places rubber covered wire must be used.
Wires must always be protected with porcelain tubes passing through partition walls, girders, and where they pass over pipes, and other wires, etc.
Incandescent lights are merely globes with a vacuum in which a filament of tungsten or some other highly resistant material meets the electric current and glows through its very resistant power. ”

“ Where there is room for wooden struts, as on a private right of way, they should be used instead of guys because of their more substantial character and the higher security of insulation thus obtained. Ordinary strain insulators cannot be relied on with lines that operate at very high voltages, and where guys must be used a timber four by six inches and [256] ten to twenty feet long may have the guy twisted about each end of it and be used as a strain insulator. A guy or strut should come well up under the lower cross-arm on a pole to avoid breaking of the pole at the point of attachment. ”

“ It was desirable in this instance to use the upper floors of the building for warm storage, consequently the top encasing insulation is placed on the ceiling of the sixth story, continuing to and meeting the wall insulation, which with the wall insulation encases the cold storage, as spoken of for the ideal. The floor construction is of flat ceiling type, there being no girders to contend with in piling product or installing piping. ”

“ INSULATION But when wire is finished it isn’t always finished. Since electricity spread itself over the earth in a million services, insulation in various forms has come to be almost as important as the wire itself. Insulation in its more advanced forms is a complex affair, gauged to accord with specific conditions and multiplying processes to secure the maximum of protection, both from electric current to life and property and from dampness and abrasion to the wire itself. ”

“ In general my experience tends to show that bodies which possess the highest specific inductive capacity, such as glass, afford a rather inferior insulation to others, which, while they are good insulators, have a much smaller specific inductive capacity, such as oils, for instance, the dielectric losses being no doubt greater in the former. ”

“ Whatever gauge wire be selected, it must be carefully insulated, to avoid all chance contact with nails, staples, metal pipes or other wires. The best insulation for wires employed indoors is gutta-percha, surrounded with a coating of cotton wound over it, except only in cases when the atmosphere is excessively dry. ”

“ Ordinary insulated wires are ineffectually protected by the rubber compounds used. Glass, mica, and better still, a large air gap are the only insulations that will serve, for the tremendous potential or voltage of the current must be carefully considered whenever insulation is necessary. The coil is better provided with a spring key in the primary circuit than a vibrator, it gives better control of the circuit and probably a larger and better spark. ”

“ The insulation of lightning-rods, says the Journal, is a grave error, because the insulators to some extent arrest the flow of currents of rarefied electricity, which it is the true function of the lightning-rod to facilitate. On the other hand, the insulator amounts to nothing as a barrier against a discharge of lightning, which can either pass through it or leap the short distance between the rod and the building. ”

“ The major insulation in a core type transformer consists of several large pieces of great mechanical strength, while in the shell type, there are required an extremely large number of relatively small pieces of insulating material, which necessitates careful workmanship to prevent defects in the finished transformer, when thin or fragile material is used. ”

“ Compressed air, unlike steam, may be taken long distances without condensation; in tight receivers it may be kept without any loss as long as we like, and used in mines and tunnels where steam heat would be a nuisance, or where electricity would be unsafe. Electrical drills and cutters, moreover, are liable to have their insulation harmed by working shocks, and by surrounding grit, sand or chips. In mines after a blast of gunpowder, a direct current from the main pipe quickly freshens the air; at all times the cool, pure breeze from the exhaust pipe is a welcome aid to ventilation. ”