$($id:$126011)$

Which of the following neutral conductors would be required to be counted as a current$-$carrying conductor per $310\mathrm{.}15($E$)?$

a$.$ The neutral conductor of a $12-3$ Type MC$,$ metal$-$clad cable installed in an office building supplying $2$ circuits of discharge lighting where the service is rated $120/208-$volt $3-$phase.

b$.$ The neutral conductor of a $12-3$ Type NM$,$ nonmetallic cable installed in a dwelling unit supplying receptacle outlets in a kitchen where the service is rated $120/240-$volt single$-$phase.

c$.$ The neutral conductor of a $12-4$ Type MC$,$ metal$-$clad cable installed in an office building supplying $3$ circuits of electric space heating equipment, the service is rated $\frac{120}{208}-$volt $3-$phase.

d$.$ The neutral conductor of a $14-3$ Type NM$,$ nonmetallic cable installed in a dwelling unit supplying LED lighting where the service is rated $120/240-$volt single$-$phase.