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 fluid, and covered with a lead sheath. When failures occurred on this type of system, the procedure for finding the failure was, to locate the manhole where smoke or flame was coming out of the manhole cover. In the event smoke was not seen, the procedure called for re-energizing 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 sufficient 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.
