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buried in the plaster, or if it were strung through the spaces between floors and ceilings and in hollow walls. Though wire covered with a good insulation was often run in this way, a number of difficulties were soon met with. Carelessness in drawing the wire through confined places abraded or stripped the insulating covering; workmen sometimes pierced the insulation or even cut the wire, with nails and tools; and there proved to be alkalies and acids in the plaster that sooner or later broke down all resistance to electrical pressure. Moreover, these methods of wiring left no way to make repairs. In the event of a failure, there was no remedy but to tear the wire out of the plaster, or to pull it out of the spaces in the walls and ceilings, leaving no way to replace it.
There are now two approved methods of running wires for low potential circuits; they may be supported on non-combustible insulators, or they may be run in conduits. Wires may be run between floors and ceilings, in the hollow spaces in walls, or in any place one wishes, if the conductors are supported wholly on non-combustible insulators, such as glass or porcelain; if the wire has an approved insulating covering; and if in passing through walls, floors, timbers, ceilings, etc., proper insulating bushings are used. Wiring by this method can be made safe and satisfactory if the work is done conscientiously. Carelessness may, however, leave vulnerable places for the carpenter's nail; there is no certainty after the work is finished that it has been properly done; and it is difficult to replace wiring that from any cause becomes defective. The greater of these disadvantages may be overcome if the architect will make provisions for the free access to the wires as he sometimes does to pipes. Accessible wire ways on or in the walls should be provided for upright wires, and floors should be arranged so that any part of the horizontal wiring can easily be reached. When these precautions are taken, this method of wiring on insulators may be made safe, trustworthy, and convenient.
The greater part of the concealed wiring in the larger buildings is now done, however, in conduits. The building is first fitted with a system of waterproof, and to some extent fireproof, tubes, much as if a twin system of gas-pipes were being installed. These tubes lead from the mains to the branches, and from the branches to the lamps, and wherever a wire is to be connected to another wire, a "junction-box" is provided. The wires are then drawn through these tubes and the necessary connections made. The tubes are not depended upon for insulation, but are simply raceways for the wires, protecting their insulating covering from injury, and affording a confined channel through which new wires may, at any time, be drawn. Aside from the accessibility, there is the advantage with this method, that though the conduit is installed at the time the building is erected, the actual wiring may be left until all carpenters and finishers have gone, and when there is no longer danger from carelessly driven nails or slashing tools. The space required for the conduits is less than that needed for porcelain insulators, which is of importance in the larger installations.
It seems probable that conduit, in some form, is the last stage in the development of concealed wiring. For some time it has been possible to get wire covered with an insulation of very good quality, and the trouble has been that this insulation was not protected from mechanical and chemical injury. A proper conduit will protect the insulation; it makes possible a more suitable time for running the wires; it gives compact construction and what may properly be called an electrical sygtem; and it makes this system of wires capable of change or renewal at any time.
But with any method the electrical features should have consideration when the building is designed. This does not make necessary any great changes in construction or in arrangement, and a little attention given to desirable provisions makes the wiring installation a part of the whole building system rather than simply an adjunct; it also gives system to the wiring itself, and insures its being better and more convenient. Where conduits are used, the plaster may entirely cover the smallest tubes, but the larger mains require channels in the walls. In many cases, it is advisable to have the larger tubes in channels provided with removable covers, for the largest wires are not drawn in and out of the tubes with facility. Provision should also be made for the closets or pockets that are to hold the fuse-blocks and switches. These details are not unfrequently left for the electrical contractor, but there is, of course, a distinct advantage to both him and the architect to have cutting avoided where possible, and when it is necessary, to have it decided upon and arranged for beforehand.
THE NATIONAL CODE OF RULES FOR ELECTRIC WIRING.
The rules for electric wiring that have been compiled and formulated by the underwriters have now become the accepted code throughout the country. Though the influence of the underwriters has, of course, done much to bring this about, there could not be the present broad acceptance, if the rules did not specify what experience has shown to be necessary for good and safe service.
One sometimes hears the criticism that these rules are the arbitrary prescriptions of men who know nothing about electricity, and who are carried away by fancied dangers. Such criticism is wide of the mark, and comes from erroneous ideas of the way in which the insurance code has grown. It is not an autocratic pronunciamento, but the result of a natural development. Starting with a few restrictions that were plainly necessary, the code has been gradually added to and expanded, as experience has shown the faults of practice. Many of the rules were adopted