Telephone subscriber loop test system

An antiparallel rectifying switch (ARS) for connecting between a telephone company line and subscriber equipment for locating faults comprising

• a first input and output,
• a second input and output, and
• paths between respective inputs and outputs providing low turn on thresholds in one direction between respective inputs and outputs and high turn-on thresholds in the other direction, the directions of low and high being the same for both sets of inputs and outputs

Apparatus for locating faults in a telephone system comprising

• remote isolation devices between subscriber equipment and respective telephone company lines of a telephone company network, at least some of said remote isolation devices being antiparallel rectifying switches (ARS's) that inhibit alternating current (A.C.) flow in one direction but not the other,
• measurement means for applying an A.C. test signal to a said telephone company line that has been connected to a said ARS and for measuring a resulting signal, the condition of said resulting signal being different if there is a fault on said telephone company line than if there is a fault in the associated subscriber equipment, and
• processor means for determining whether a fault is on said telephone company line or subscriber equipment based upon said resulting signal.