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will lead into serious error, but they are put out with the hope that in their proper use constructing engineers, architects, and others called upon to get out specifications may be relieved of much of the petty detail accompanying such work, which, though important, is too often neglected on account of its tediousness and the time it consumes.
In fact, the conditions under which electric light plants must be installed to meet the varied requirements arising from the diversity of their application are so numerous that many of them it is impossible even to mention in a general specification. Though it is expected that these specifications will be found sufficiently full and explicit for some of the smaller installations, not requiring special appliances or precautions, in the majority of instances a careful study must be made, for reasons which will suggest themselves, of the surrounding conditions and limitations.
In a large class of installations no small amount of judgment, ability and ingenuity is often required to overcome difficulties met with, to adapt the material at hand to new purposes, or to devise new methods for securing unusual results; in such instances especial care should be taken in the details of the specifications in order that bidders may thoroughly understand all the requirements and conditions, thus leaving no excuse for poor workmanship or materials on the score of inadequate information from which to make
estimates, an excuse that too oîten has a large foundation on fact. Among such installations may be named:
Art Galleries, Museums, etc. Hospitals.
Hotels, Apartment Houses, etc. Bleacheries.
Mines, Shafts, Tunnels, etc. Breweries, Distilleries, etc. Oil Works. Chemical Works and Labor. Paper and Pulp Mills. atories.
Prisons and Penitentiaries. Canning Factories
Packing Houses. Cold Storage Warehouses. Slaughter Houses. Dye Houses.
Tanneries. Flour and similar mills. Theatres, Concert Halls, etc Fabric Mills.
Vessels. Finished Residences.
As an example of the extent to which such study and analysis should be carried before making a detailed specification let us take the last type noted, that of vessels. Here such various requirements and conditions imposed by questions of safety, reliability, utility, economy, or æsthetic effects are met with that almost invariably a particular specification must be made out for each installation. For whatsoever purpose the plant is installed, however, safety and reliability should be the first considerations. On account of the disastrous results that might accompany the extinguishment of the lights on shipboard it is of the utmost importance that 110 device that can increase the safety and reliability of the plant shall be omitted, and that the utmost care shall be exercised in every part of the installation, Economy should never be more than a secondary consideration,
Nearly, if not quite, all plants installed on shipboard are arc plants or low-potential, direct-current incandescent plants. The former are, for the most part, confined to small excursion boats, river barges, scows, dredges, etc., the conditions and requirements comparatively simple, and the specification may be made up from the general form for arc plants. For incandescent plants on similar boats the specification is equally simple, but for the larger plants, especially on sea-going vessels, the necessary modifications are numerous and important.
A careful study should be made of the purpose for which the plant is installed; the material of which the boat is built; the character of the cargo; the class of passengers; the length of voyages or trips; temperatures and vapors to which the apparatus and appliances will be exposed; character of the power; limitations of speed, weight, space, etc.; method of connecting engines with dynamos; duplication of parts for renewals, repairs or extensions ; magnetic effects; location of switches and cut outs; location and manipulation of search lights or projectors, flash lights, signal lights, etc.; motors; and any special devices that may be operated from the dynamo circuits. There should be supplied with the dynamos a complete set of wrenches, screw-drivers, pliers, oil cups, oil cans, drip pans, guard rails, extra brushes, bearings, and such other tools and appurtenances of the most approved kind as are necessary in their operation, care, and maintenance. There should be furnished in addition to the ordinary regulating apparatus a tachometer, or speed indicator, an efficient apparatus for testing insulation, and at least one portable voltmeter and ampère meter of known accuracy and reliability. Compound wound or automatically regulated dynamos are in general preferable to shunt wound and hand regulated dynamos.
The switchboard should be so arranged that any circuit or circuits may be attached to any dynamo; that dynamos may be operated separately or in parallel; that any dynamo may be added to or taken from the circuit quickly and without disturbing the operation of the remaining dynamos in circuit, or causing any change in the lights.
Special attention should be paid to the character of the insulation. Climatic and temperature effects should be considered. The dynamos, all wires, fixtures, metal junction boxes, switches, receptacles, and other apparatus or appliances carrying current, should be carefully insulated from the ship. All junction boxes, switches, conductors, and entrances to fixtures should be water-tight. Wires should pass through bulkheads and decks, junction boxes, etc., in water-tight stuffing boxes. Where necessary, lamps and sockets should be inclosed in waterproof globes. All cut-outs, switches, etc., should be of moisture proof, incombustible material. Joints will prove a source of trouble unless made with extreme care. Sockets, binding screws, switches, receptacles, shade holders, etc., must be protected from corrosion. Circuits should be so arranged that no part of the vessel will be in darkness through the failure of a single circuit. The wire should be figured with an ample margin in carrying capacity. The size, character, and position of search lights and projectors will be determined by local conditions. Permanent signal lights should be provided with a duplicate light, which is automatically switched into circuit when the first lamp fails and gives a signal calling attention to the failure of one lamp Where necessary, springs should be provided to guard lamps or fixtures from injurious shocks. Lamps should be adapted to the purpose for which they are to be used both as regards candle power and economy. In the selection of measuring instruments such as voltmeters and ammeters not only must the effect of the rolling and pitching of the vessel be considered, but also the magnetic effect of the iron and steel used in the construction of the vessel and the proximity of large masses of iron and steel in engines, shafting, etc. Cut-outs and switches should be plainly labeled with the location of the circuit and number of lamps. Lights to be controlled by passengers should be provided with a card containing printed instructions concerning their use.