Do not listen to what Chaz said about electrical code. He clearly doesn’t know what he is talking about- for instance, stranded wire, otherwise known as THHN, is run almost exclusively in EMT metal conduit for commercial and industrial applications in North America, which is exclusively 60Hz. Stranded wire is used for dryer cable, stove cable, 6AWG cable for hot tubs and subpanels, and then there are service conductors.
Also, do not listen to anyone who tells you to use 12/3 or 14/3 or any Romex or BX 3 conductor cable for common neutral and two hots on the same leg. That is a fire hazard and is against all electrical codes. Shared neutral is permitted in split phase when the hot conductors are wired to opposite legs. That is because the neutral return current is 180 degrees out of phase between the two hot conductors, which reduces loading on the neutral when both circuits are loaded with similar loads. This works best with lighting on both legs. Don’t try putting a clothes washer on one leg and your lighting on the other unless you want to replace lightbulbs every month.
Bottom line is that you should only make changes to your electrical system if you are qualified. Otherwise, pay a licenced electrician to do the job right, and get permits for the work and have it inspected by the proper electrical safety authority.
