Abstract :
F. R. Cutcheon: Mr. Langan objects to the puncture test for insulation on the supposition that the insulation may stand up well under test and deteriorate very rapidly thereafter. In cable work it is common practice to specify that the puncture test shall be repeated at stated intervals, usually covering a period of five years; I believe that this overcomes the objection, and with this provision the puncture test is the most reliable. Insulation resistance, in my experience, has proved of no value as an indication of the condition of a cable; this is especially true of multiple-conductor cables for high voltage, since the contact with the lead is very slight if it exists at all. The jute filling will serve to give a high-insulation test, but will break down when subjected to a high voltage.
