I am putting in a 1/2 bath and I am planning my electric. I will be running my current 20amp bathroom receptacle circuit to this new bath so they can share that circuit. Can the new bathroom share a light circuit with the hallway light circuit or should I be running the current bathroom light circuit to the new bathroom lights? So, the two bathrooms would share a circuit for the receptacles and a circuit for the bathroom lights?
Yes, bathroom lighting and other hardwired loads are always allowed to be on other, non-bathroom circuits, except for these particular ones:
- Not Kitchen countertop circuits, since they must be dedicated to that. NEC 210.11(C)(1)
- Not the laundry room circuit, since it must be dedicated to that. NEC 210.11(C)(2)
- Not a bathroom receptacle circuit that serves other bathrooms. (NEC 210.11(C)(3) which is what ThreePhaseEel is talking about.)
- However, it's allowed if the bathroom recep circuit serves only this bathroom.
So for instance, suppose your existing bathroom recep circuit, the one you want to extend, already serves non-bathroom loads, but it's "grandfathered" because this was setup before Code changed. That's fine; it gets to stay grandfathered; but you can't use it for the new bathroom. At all.
The rule of grandfathering is you can't make the situation worse.
Having the bathroom lights on the hall light circuit is fine
Since you are providing the bathroom receptacles with power extended from an existing bathroom receptacle circuit, instead of providing the bathroom in question with a combination receptacle and lighting circuit dedicated to that bathroom, we can power the bathroom lighting from any general lighting circuit. This is simply a function of NEC 210.11(C) ((C)(3) for the bathroom case, where the Exception to that section is what allows the "1 circuit for the whole bathroom" approach) only discussing receptacles, not outlets in general.