Procedure
This test shall be made on the sample length before any other electrical test.
All outer coverings shall be removed and the cores shall be immersed in water at ambient temperature for at least 1 h before the test. The d.c. test voltage shall be between 80 V and 500 V and shall be applied for sufficient time to reach a reasonably steady measurement, but in any case for not less than 1 min and not more than 5 min. The measurement shall be made between each conductor and the water. If requested, measurement may be confirmed at a temperature of (20 ± 1) °C.
Calculations
The volume resistivity shall be calculated from the measured insulation resistance by the following formula:
The “insulation resistance constant Ki” expressed in megohms ⋅ kilometres may also be calculated, using the formula:
NOTE For the cores of shaped conductors, the ratio D/d is the ratio of the perimeter over the insulation to the perimeter over the conductor.
Requirements
The values calculated from the measurements shall be not less than those specified in Table 13.
