ABSTRACT
Underground systems originally established for concentrated areas such as cities or towns consisted of cable installed in conduit systems and terminated in manholes. The manholes provided a space to join sections of cables and in some cases, a place to install transformers and switches. Cable construction used in these systems consisted of paper insulation, impregnated with an insulating ®uid, and covered with a lead sheath. When failures occurred in this type of system, the procedure for Žnding the failure was to locate the manhole where smoke or ®ame was coming out of the manhole cover. In the event smoke was not seen, the procedure called for reenergizing the faulted circuit to produce the detectable smoke location. If this did not work, or if there were other operating problems, a device such as a high voltage transformer could be used to breakdown the failure and generate sufŽcient smoke for the purpose of detecting which manhole contained the failure. If the fault was found in a manhole or if the fault had occurred in a cable between manholes, no further locating procedures were required. This was because the entire section of cable between adjacent manholes had to be replaced.
