Where a $240-$volt, single$-$phase, $2-$wire separately derived system is grounded by choice, the requirements in $q,$ must be applied to the installation.

a$.250\mathrm{.}24$

b$.250\mathrm{.}30($A$)$

c$.250\mathrm{.}30($B$)$

d$.250\mathrm{.}50$