The CZ3000 is a fault location instrument for the precise location of insulation faults on telecommunication cable.

NOTE: The MKII needs a good wire for testing and the MKIII doesn't. Below is the paragraph extracted from the CZ3000MKIII manual.
The CZ3000MKIII provides two methods of fault location. The traditional "good wire" method, where either one or two wires of high insulation integrity must be present between the test position and the end of the cable, and the "Kupfmuller method" that allows accurate fault location where no "good wire" exists. With both methods of fault location implemented in the one instrument the location of even the most difficult faults is made easy.