Insulation Resistance

Tweakers' Asylum

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Thanks to friend and Posthole Digger, Mahatma Kane Jeeves, I was able to get an equation for insulation resistance which would answer what cheap-Jack seemed to be asking about it previously. The equation is:
R = (rho/2piL)ln(d2/d1) where R is resistance in Ohms, rho is resistivity, L is the length of the line, d1 is the inside diameter and d2 is the outside diameter.
So, for a 1 meter (100cm) length of wire insulated with 1mm thickness of cotton, and assuming 10⁹ ohm-cm for the resistivity of cotton, R will be about 1.75 Megohms.
In other words, if you were to make a coaxial cable of this construction with a 1mm diameter center conductor and 1mm thickness of cotton insulation surrounded uniformly with an outer conductor, R is what would be measured between the center conductor and the outer conductor.
Also for what it's worth, while MKJ wasn't able to find any other reference for cotton's resistivity, he feels that the 10⁹ ohm-cm is rather too low.
se

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Topic - Insulation Resistance - Steve Eddy 12:21:30 04/04/07 (4)

Correct or not, thanks for yr good work. - cheap-Jack 09:06:16 04/05/07 (0)

Re: Insulation Resistance - clifff 12:33:41 04/04/07 (2)

Bingo - Cpk 15:20:10 04/04/07 (0)

Re: Insulation Resistance - Steve Eddy 13:25:30 04/04/07 (0)

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