Identifier: americantelepho00mill (find matches)
Title: American telephone practice
Year: 1905 (1900s)
Authors: Miller, Kempster B. (from old catalog)
Subjects:
Publisher:
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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hand side of this figure. In thiscase the available power is direct current at 500 volts, and the mainspass first through fuses of sufficient carrying capacity, thencethrough the main switch adapted to cut off the entire power backof all apparatus, and thence through arresters for the protection ofthe power apparatus. These consist of an air-gap and a choke-coil of low resistance, but high impedance, in each side of the powercircuit. Each lead then passes through another fuse, and thenceto the power switch-board proper. An ammeter and a wattmeterare here shown for measuring the total current, and the total energydelivered to the power board. It is not the practice of the inde-pendent companies, as a rule, to furnish the wattmeter on thepower board, for the reason that this is usually supplied by the com-pany furnishing the current, and is mounted by them in some por-tion of the power circuit outside of the power board. At the point A the main circuit divides into three separate leads,
Text Appearing After Image:
548 AMERICAN TELEPHOXE PRACTICE. two of which extend through separate pairs of fuses to the single-throw, double-pole knife switches, B and C, controlling respectivelythe motors of charging machines, Xos. I and 2, the generators ofwhich supply direct current for charging the storage battery forthe supply of all direct current to the exchange. The third branchof the main power lead extends to the knife switch, D, which con-trols the motor side of ringing machine Xo. 1, used for supplyingalternating and pulsating current to the subscribers lines for ring-ing, and also for other minor purposes, which will be pointed outlater. Bridged across the main power leads are the lamps for lightingthe power switch-board, these being arranged in any suitable man-ner, in accordance with the voltage across the power mains. Inthis particular case, where 500 volts direct current is used, five 100-volt lamps are placed across the circuit in series, and these are con-trolled by a double-pole cut-out of th

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