Insulation Test of Telephone Cables and Wires and Minimum Insulation Resistance values

TM 11-6625-298-14

(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.

Figure 3-5. 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

sistance values

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

the same manner as power cables (para 3-11a

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

satisfactory.

megohm-miles.

(4) If the insulation resistance of a bunch is

NOTE

less than that given in the table 3-2 below,

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

3-7