Background info on Megger's TDRs

18 February 2014

Time Domain Reflectometers (TDRs) can actually pinpoint the location of faults on cables, and are available in convenient handheld models. There are two principle considerations that affect their application and should be accounted for prior to purchase: TDRs cannot test single-core (single-conductor) wire. NO TDR can test single-core. TDR technology is based on generating an energy pulse that travels between parallel conductors equidistantly separated (uniform insulation thickness). Only one conductor? Cannot use a TDR. Small, handheld TDRs can accommodate virtually type of communication application; twisted-pair, coax, control wiring, etc. These types of cables are sufficiently light and uniform in construction to be accommodated universally. Moving to power cable, however, introduces a new set of parameters. Don’t expect a handheld TDR to find faults on heavy-gauge power cables. It might, if the fault is bolted or wide open. But heavier gauges introduce high resistance faults, generally those over 100 ‡. These more sophisticated faults require more sophisticated test equipment; i.e., a TDR-“thumper” combination.