Question

A cylindrical rubber insulated cable has a diameter of 0.18 inch and an insulation thickness of 0.25 inch. If the specific resistance 0f rubber is 1014 ohm-cm, determine the insulation resistance per 1000 ft length of the cable.

Answer 1

Solution;

Given;

d=0.18in

$r=0.09in$

$t=0.25in$

The outer radius is;

$R=0.09+0.25=0.34in$

Specific resistance of rubber;

$\delta=10^{14}\Omega-cm=10^{12}\Omega-m$

Length $L=1000ft=305m$

Insulation resistance;

$R_{in}=\frac{\delta}{2πL} ln(\frac Rr)$

$R_{in}=\frac{10^{12}}{2×π×305}ln(\frac {0.34}{0.09})=693.569M\Omega$