at which the supply of the first timing signal following the line breakage to the first input terminal a ceases at which time the control circuit can 34 sense 34 the signal supplied to the second input terminal b the control circuit in turns begins to generate an output signal this signal supplied to the control terminal of the circuit biasing means p causes the cut off of parts of the telephone circuit itself and the disconnection of the supply to the subscriber 39 s telephone line thus stopping electrical energy from being consumed as a result of the breakdown as long as the grounded cable condition persists the control circuit c continues to generate the cut off signal during all of the time intervals between the timing signals during the short time intervals in which the timing signals are supplied to the first input terminal a the line is again supplied and the control circuit can again detect the grounded cable condition and control the cut off after each timing signal until the following signal as soon as the grounded cable condition is repaired the comparator no longer generates any output signal even when the line is supplied again consequently at the end of the supply to the first input terminal a of the first timing signal following or simultaneous with the repair of the breakdown the control circuit c sense the removal of the grounded cable condition and allows the line to continue to be normally supplied it can be seen that in this way current consumption limited in any case by the protection already included in the.