File:American telephone practice (1905) (14569741149).jpg

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

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enable a subscriber who has been called upfor test to converse with the wire chief. The various tests commonly employed by the wire chief in locat-ing trouble on common battery lines are divided by the Bell Com-pany in its specifications for testing with its standard wire chiefsequipment as follows: First, tests for grounds; second, tests forthe continuity of currents; third, tests for crosses; fourth, ballistictests; fifth, tests for continuity through condensers and repeatingcoils; sixth, tests for determining the presence and magnitude offoreign currents; seventh, tests for locating trouble in the switch-board ; eighth, miscellaneous tests. These will be briefly taken upin their order. Tests for grounds may be made in two ways, by means of thevolt-meter, or by the use of relay, R, connected through key, No. 5.In order to make clearer the methods of volt-meter testing forgrounds, and of measuring the resistance of a circuit to ground or ■^ C> 01 ± oj ro ^ -Jn 3
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644 AMERICAN TELEPHONE PRACTICE. of any other circuit by means of the volt-meter, the cord circuit ofFig. 472 has been redrawn in part in Fig. 473, all parts not directlyconcerned in volt-meter tests being omitted. In making tests for grounds, throw the volt-meter key, No. 4, leav-ing the other keys in their normal positions. This will place the40-volt coil of the meter in a circuit between the ground and thering side of the line under test, the circuit including the 40-voltbattery. If a ground exists on the sleeve side of the line, the volt-meter will be deflected, owing to the passage of current through it.The same test may be made with respect to the tip side of the lineby throwing the reversing key. The resistance of the ground may be measured by noting theamount of deflection. In the arrangement shown, the 40-volt coil ofthe volt-meter has a resistance of 100,000 ohms, and the 4-volt coil,10,000 ohms. The shunting key, when closed, places a shunt of1,111 ohms around the 4-volt co

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