Patent ID: 7710122

Claim:
A circuit for measuring resistance to ground on a telecommunications paired cable including a designated telephone pair having a tip side and a ring side in communication with a central office power supply, said circuit comprising: a first electrical lead for connecting to a ground to be tested; a second electrical lead for connecting to the ring side of the designated pair which returns to a central office power supply; a third electrical lead for connecting to the tip side of the designated pair which returns to a central office ground; a fourth electrical lead for connecting to a voltage rod removably inserted into the ground; a switch connection including a first condition where loop current is not flowing from the central office power supply to the ground to be tested and including a second condition where loop current flows from the central office power supply to the ground to be tested; a first measurement means for providing a first DC voltage measurement of voltage between the first lead connected to the ground to be tested and the fourth electrical lead connected to the voltage rod when the switch connection is in the first condition and a second DC voltage measurement of voltage between the first lead connected to the ground to be tested and the fourth electrical lead connected to the voltage rod when the switch connection is in the second condition; a second measurement means for providing a measurement of current flowing from the first electrical lead connected to the ground to be tested to the second electrical lead connected to the ring side of a designated pair which returns to a central office power supply when the switch connection is in the second condition; a processor means for subtracting the second DC voltage measurement from the first DC voltage measurement to provide a station ground voltage fall; a processor means for dividing the station ground voltage fall by the measurement of current to compute resistance in the ground to be tested.