Abstract: There are disclosed apparatus and methods for testing a live circuit powered from an alternating current (AC) voltage. A live circuit tester includes a spread spectrum time domain reflectometer (SSTDR) configured to perform SSTDR measurements of the live circuit and a memory storing one or more ignore distance values. A processor coupled to the SSTDR and the memory detects a potential fault in the live circuit based on results of one or more SSTDR measurements, the potential fault associated with a distance from the apparatus. The processor compares the distance associated with the potential fault with each of the one or more ignore distance values, and stores, in the memory, data defining the potential fault if the associated distance does not match any of the one or more ignore distance values.

Abstract: There are disclosed apparatus and methods for testing a live circuit powered from an alternating current (AC) voltage. A zero crossing detector detects zero crossings of the AC voltage. A spread spectrum time domain reflectometer (SSTDR) coupled to the zero crossing detector performs measurements of the live circuit, each measurement synchronized with a zero crossings of the AC voltage. A processor coupled to the SSTDR detects faults in the live circuit based on correlation data provided by the SSTDR.