Using a shared neutral for two circuits was a common practice to save on wire. It's allowed as long as the two circuits are connected to different legs/phases o

Using a shared neutral for two circuits was a common practice to save on wire. It's allowed as long as the two circuits are connected to different legs/phases of the electrical panel. More recent versions of the NEC require that the breakers used for both hot legs of such circuits be linked so turning one circuit off also turns off the other. Common neutrals on residential branch circuits have largely fallen out of favor for new construction due to requirements for GFCI or AFCI protection on most circuits.