(b) After all measurements are completed,
reading. This will eliminate any error that
discharge the cable by grounding all conductors.
might be caused by the electrostatic
capacity of the cable.
Connections for measuring one cable
conductor to ground.
b. Power Wires. Test the insulation of individual
usually have a higher insulation resistance
value, a 2-mile length will have en in-
power wires in the same manner as cable con-
sulation resistance of 250 megohms, a 10-
ductors (a above). Make the GROUND connection
mile length will have an insulation
to the outer sheath, or jacket, of the wire.
resistance of 50 megohms, etc.
3-12. Insulation Test
of Telephone Cables
(2) When testing the insulation resistance of
and Wires and Minimum Insulation Re-
large exchange cables, divide the pairs into
bunches of 25 to 100 pairs per bunch. Test each
a. Testing Insulation Resistance.
bunch as a single conductor of a power cable.
(1) Test the insulation of exchange cables in
(3) If the insulation resistance of a bunch is
not lower than a single pair, assume that the
above). The conductors of these cables, when new,
insulation resistance of all pairs in that bunch is
should have an insulation resistance of at least 500
(4) If the insulation resistance of a bunch is
A conductor is said to have an insulation
separate the wires and measure each separately
resistance value of 500 megohm-miles when
against all other wires grounded to that sheath.
the insulation resistance of a 1-mile length
is 500 megohms. Because short cables