A single core lead covered cable is to be designed. Its conductor radius is $0\mathrm{.}6$ cm $.$ Its three insulating materials A $,$B and C have relative permittivities of $3\mathrm{.}0,4\mathrm{.}0$ and $2\mathrm{.}5$ with maximum permissible stresses of $50,55$ and $40K\frac{v}{c}m$ respectively. The thickness of the outer layer of insulation is $0\mathrm{.}3$ cm $.$

Determine the permissible voltage of the cable?

Determine the ungraded Cable size, for the same permissible voltage of a homogeneous dielectric of material C$.$