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tem 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.

CHAPTER V.

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

from the regulations enforced by the better class of electric companies, other rules have been suggested and formulated by some of the best-known engineers, and the underwriters now have a corps of electricians trained to judge of construction with regard to safety from fire, and competent to impose restrictions as new conditions are presented. If the rules were unreasonable, the electric-light companies would be the first to protest; but, on the contrary, the National ElectricLight Association has adopted virtually the same rules, and electrical engineers in general accept the insurance code as the best existing guide for safe construction. The complaint that comes from the better class of electrical men is not that the rules are too exacting, but that they are not always rigidly and consistently enforced.

Architects can, of course, do much to insure good electrical construction in their buildings, but they have usually paid little attention to this feature. It is very common to find in the architect's specifications a clause requiring "all work to be done in strict compliance with the underwriters' rules," and then to find, following this, a number of clauses specifying construction that is explicitly prohibited by the rules. With this evidence of ignorance before them, it is not surprising that contractors often feel free to do the work as they please.

The rules are necessarily short, and naturally there are many technical terms used. It has seemed that it would be helpful to have these terms defined, and to have the reasons for the rules briefly stated. Accordingly, the latest rules of the National Board of Fire Underwriters, as amended at New York, January, 1895, are taken up here. The rules, which are printed in small type, must be read continuously to get the full meaning, since the remarks are interpolated. The advantages in taking up a few rules at a time seemed greater than the disadvantages in having sometimes to refer to the last sub-heading in order to find the subject.

CLASS A.

CENTRAL STATIONS. FOR LIGHT OR POWER.

These rules also apply to dynamo rooms in isolated plants, connected with or detached from buildings used for other purposes; also to all varieties of apparatus therein, of both high and low potential.

1. Generators:

a. Must be located in a dry place.

b. Must be insulated on floors or base frames, which must be kept filled, to prevent absorption of moisture, and also kept clean and dry.

c. Must never be placed in a room where any hazardous process is carried on, nor in places where they would be exposed to inflammable gases, or flyings of combustible material. d. Must each be provided with a waterproof covering.

A "generator" receives mechanical energy at the pulley, and gives out electrical energy; a "motor" receives electrical energy and gives out mechanical energy at the pulley. Strictly speaking, both are "dynamos," or dynamo electric machines, but the "dynamo" is commonly used as synonymous with generator.

term"

"Potential" is used in the rules as synonymous with electrical pressure; voltage; electro-motive force the

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כתח

FIG. 9.-Base Frame.

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virtue by which an electric current is forced through a wire or other substance. High" and "low" potential are, of course, relative terms, but in these rules a high potential is that measuring over 300 volts, and a low potential is that measuring 300 volts or less.

The "base frames," on which dynamos are usually set, are simply heavy frames of wood, filled, or impregnated, with oil or other insulating substance that will prevent moisture from penetrating the pores of the

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