 To more easily understand the problem about earth currents which especially are interferring devices of the telephone network, please study the scheme above. Assume that your phone line is free. Under this condition I approximately measured DC -4 volts from one of the conductors of phone line to ground. From the other conductor to ground I approx. got DC -52 volts. The voltage between the conductors is as follows: -4V - (-52V) <=> -4V + 52V <=> 48 V. By the statements above the positive polarity of DC supply has to be connected to ground, at the call-office. Suppose it's raining and the air humi- dity is increasing. An increased humidity seems to increase the conductance (the ability of electrical distray) of all materials. The ground current IGND was measured to a value between 3 and 15 ľA. Through the outdoor bell is floating IGND = IGND1 + IGND2. The both currents IGND1 and IGND2 are passing the local ring generator RSG. After the RSG the whole sum of IGND1 and IGND2 nearly floats in the upper conducter of the picture. Finally you're able to remove the ground fault by connecting a ground disuniter between the RSG and the bell. (RSG = Ring Signal Generator.) My ground disuniter: |
