File:American telephone practice (1905) (14569722958).jpg

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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and machines together, to the exchange. Practice differs to aconsiderable extent as to what degree means should be provided formeasuring the various branch discharge leads, but the arrangementshown in this figure (397) is thought to be fairly representative ofstandard practice. A shunt, z2, is provided in that discharge leadwhich supplies the keyboard signals for both A and B operators, butif it is desired to measure the keyboard signal current of the A ope-rators separately from that of the B operators, this may be done bydividing the bus-bar, T, as already pointed out, and placing theshunt in circuit with each of the leads to the bar so divided. Another shunt, z5, is placed in the discharge lead, v, which sup-plies the bus-bar, V, from which the line lamps, the operators trans-mitters and the line relays are supplied with current. Still anothershunt, z4, is placed in the lead from the live side of the battery tothe repeating coil rack, and as all current for talking purposes is fed
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556 POWER PLANTS FOR COMMON BATTERY SYSTEMS. 557 through the repeating coils, this shunt serves to measure the entirecurrent consumed by the subscribers lines in talking. Of course, it is possible to effect a greater subdivision of the cur-rent, as for instance, a shunt might be placed in each of the leads,w, w and w, instead of having a single shunt to measure the cur-rent consumed by all of these leads. There is very little advantage,however, to be gained by too great subdivision in this respect, as itmerely serves to complicate matters unduly, and very often thecurrent in one set of leads alone would be so small as to render itsmeasurement on the ordinary ammeter provided, almost an im-possibility. Coming now to the actual construction of the power board, Fig.398 gives a good idea of a modern board furnished by the KelloggSwitch-Board and Supply Company in one of the large centraloffice equipments of the Keystone Telephone Company in Phila-delphia. This board is of marble, and all

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