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is evidently unsafe to have the machine placed where there is inflammable matter.

The waterproof cover that is required, serves to keep the dynamo clean and dry under ordinary conditions, and will be ready to use in case of a leak above the machine or for protection from water damage in case of a fire.

2. Care and Attendance:

A competent man must be kept on duty in the room where generators are operating.

Oily waste must be kept in approved metal cans, and removed daily.

[Approved waste cans shall be made of metal, with legs raising can three inches from the floor, and with self-closing covers.]

3. Conductors:

From generators, switch-boards, rheostats or other instruments, and thence to outside lines, conductors —

a. Must be in plain sight, and readily accessible.

b. Must be wholly on non-combustible insulators, such as glass or porcelain.

C. Must be separated from contact with floors, partitions, or walls, through which they may pass, by non-combustible insulating tubes, such as glass or porcelain.

d. Must be kept rigidly so far apart that they cannot come in contact.

e. Must be covered with non-inflammable insulating material sufficient to prevent accidental contact, except that“ busbars” may be made of bare metal.

f. Must have ample carrying capacity, to prevent heating. (See Capacity of Wires Table, page 135.)

The “switch-board” is the frame, board, partition, or slab on which are grouped the different instruments, and the devices for controlling the dynamos and for properly distributing the currents to the different circuits. (Page 64.)

A “resistance-box” contains usually a number of coils of wire, and its object is to introduce into the electric circuit a resistance that will reduce the strength of the current. It is thus a sort of electrical throttling device. A “rheostat” is an adjustable resistance-box. An “equalizer” is a resistance-box or rheostat used for the special purpose of equalizing conditions in different parts of a circuit. “Resistance-box” is the general term and is applied to all this species of apparatus. (Page 66.)

There are innumerable types of “insulators” for supporting wire, and they vary in shape according to the special purpose for which they are used. Sketches of a few of them are given in Figures 11–14.

Where wires pass through floors, walls, and such places, there is particular liability to dampness, and to contact with material that offers a path for leakage. In such places, there is also liability that the insulation

on the wire will become abraded in drawing the wire through, or that it will gradually be abraded by the movement of the wire afterward. For protection in these places " insulating-tubes” are used. There is a flange on one end to prevent the tube from sliding through the hole. (Fig. 14.)

The “ bus-bars," or omnibus bars, are the main conductors from which the smaller wires lead off to the

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FIG. 11.- Porcelain Cleat. FIG. 12.- Porcelain Knob. Fig. 13.- Petti

coat Insulator. FIG. 14. — Insulating-tube.

different circuits in the building or city. The busbars are placed on the switch-board, usually at the back. (Fig. 15.)

The “carrying capacity,” or safe carrying capacity, of a conductor is the amount of current it will carry without heating to an unsafe temperature. A certain temperature is fixed upon, and there is determined

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for each size of wire the current that in passing through it will heat it to this maximum allowable temperature. The results of these experiments are embodied in a table of safe carrying capacities for all sizes of wire commonly used. (Page 135.)

In dynamo rooms the conductors are usually numerous and very compactly placed, so that there is need of special precaution in construction. Moreover, the




FIG. 15.- Bus-bars.

wires are the main conductors of the wiring system, and any devices protecting them work only when the full capacity of the system is exceeded. Short circuits or leaks would consequently be more serious in their effects. In a part of the dynamo-room wiring, it is not practicable to have safety devices, and where so much has thus to be trusted to insulation and noncombustibility, the only satisfactory construction is to have the wires in contact with nothing but glass, porcelain, slate, or similar material.

Bus-bars are in a place where they are not exposed to contact with foreign substances, but they are to be supported on non-combustible material, as there is a possibility of their overheating.

4. Switch-boards:

a. Must be so placed as to reduce to a minimum the danger of communicating fire to adjacent combustible material.

6. Must be accessible from all sides when the connections are on the back; or may be placed against a brick or stone wall when the wiring is entirely on the face.

C. Must be kept free from moisture.

d. Must be made of non-combustible material, or of hard wood in skeleton form, filled to prevent absorption of moisture.

e. Bus-bars must be equipped in accordance with Rule 3 for placing conductors.

[Section a. Special attention is called to the fact that switch-boards should not be built down to the floor, nor up to the ceiling, but a space of at least eighteen inches, or two feet, should be left between the floor and the board, and between the ceiling and the board, in order to prevent fire from communicating from the switch-board to the floor or ceiling, and also to prevent the forming of a partially concealed space very liable to be used for storage or rubbish and oily waste.]

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