A fault detector for use with a telephone wire-pair having a return conductor and an output conductor, a method of protecting a telecommunications network including the telephone wire-pair and a power supply for the telecommunications network. In one embodiment, the fault detector includes (1) a passive sensor coupled between Earth and the wire-pair to detect a ground fault thereon, (2) an amplifier having inputs coupled across the passive sensor and configured to characterize the ground fault in terms of a value and (3) a controller configured to receive the value via an output of the amplifier and compare the value to a threshold to determine if the ground fault exceeds a safety limit.