Test device for and method of locating faults in a two-wire line or for switching two-wire lines

摘要

A test device detects current in a two-wire line, such as a telephone loop, to enable a short circuit or the like to be determined at a remote location. The current at a predetermined line location is sensed by a simple switch means. Switching of the line, such as a working line, is controlled with another two-wire line, such as a spare line. Control is provided to select one of two loads terminating the line. The test device is connected in series on one of the line wires. The test device has a constant ohmic value in a low current range when the in-line current is less than a predetermined current value. The ohmic value increases sharply to a higher value in a high current range when the in-line current is greater than the predetermined current value. The test device comprises a relay having an operate coil and a resting contact which are series-connected between the terminals of the test device, and a resistor connected in parallel with the contact.