Answer Posted / npatra

Mr. surendra's answer is very correct. But I want to
elaborate the thing again.

Resistance= Specific Resistance(S) * length of Wire(L) /
Cross Sctional Area(A).
A.)
Insulation Resistance means the Resistance that the
insulation offers to the Current to stop it from leaking to
the Ground. And It is measured between Conductor and Ground.
So IR pertains to leakage current.

So here- Cross section Area=(A1)The Area the medium(here
Insulation)that offer resistance to leakage current.
A1=PI*d * L where L is the length of the Cable, d is the
diameter of the conductor in the insulation.
Length= t= thickness of the Insulation= the Total length
that the leakage current flows.
S=Sp.Res. of Insulation material=S1

Note PI=22/7

IR= S1*t/(PI*d*L)

in the question-IR is 200 Mohm, L=250 meter,
thence d= S1*t/(PI*250*20000000)which is the diameter of
conductor wire.

B).
Resistance of Conductor is the resistance felt by main
working Current in the cable from one end to other end. It
is measured between two ends of a wire.(may be bare wire,
may be insulated wire)

Area of conductor wire(A2)= PI*d*d/4
R= Specific Resistance of Conductor * length / Cross
Sctional Area.
R= S2 * 250/(PI*d*d/4)

Considering Length as 250meter for the cable, What is
missing here is :
1.)Insulation Thickness(t)
2.)Specific resitance of Conductor (S1) and Insulation
Material(S2).


If you want to Calculate Volume-Resistivity there is
another Formula which is very diffrent and in logarithmic
form.

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