Moisture penetration in electric cable detector - uses conductors amongst armouring wires surrounded by material whose conductivity increases with dampness

摘要

A wire, or a pair of wires (10, 11) is fed under an aluminium sheath (6). The wires are surrounded with a material which is electrically isolating when dry but conductive when wet. By measurement of the resistance between the wire pair or between the wire and the aluminium sheath the presence of moisture arising from a break in the sheath may be detected. The measurement of the value of the resistance gives an indication of the length of the electric circuit and hence an indication of the location of the fault. The electric cable carries, underneath the insulation sheath, a protective screen comprising a metallic sheet. The insulator of the conductor is in direct contact with the sheet such that the detector circuit is constituted by the conductor wire and the sheet.