I have a hopefully easy (but probably not) question for y'all. Forgive my being verbose - just trying to provide the necessary information.
I recently purchased a foreclosed home; it was built in 1974 and has had a couple new additions put on and has been remodeled a time or two. The result is that the simplest of tasks here often turns into a major project to fix the mistakes of DIYers who traded 'get it done right' for 'get it done'.
During a recent attempt to simply install a 3-way switch, I found that someone had extended one of my 20A kitchen receptacle circuits using 14AWG wire. I traced back the 14 and disconnected it, effectively orphaning 3 receptacles. I'm OK with 2 of them not functioning - they're in the way of a future French door anyway - but I would like to restore one.
This one is in a 2-gang box with the switch that controls my garbage disposal. There is a MWBC running into this box via a 12-3 cable.
One branch handles the garbage disposal and the dishwasher. The black live is connected to a switch & a second ("downstream") 12-3. The live on the source 12-3 goes directly to the receptacle, providing always-on power to the dishwasher. The red from the downstream 12-3 connects the switch to the receptacle, allowing that plug - and the disposal - to be powered on/off via the switch.
The other branch appears to go out to my patio and controls 3 ceiling fan/light fixtures and 2 dry receptacles. The red is live from the source. The neutral is wirenutted into the all of the neutrals from the other branch. The live red is wirenutted to a black wire in 12-2 cable. The black then heads out to power 3 ceiling fan/light fixtures and 2 dry receptacles in my patio area.
The three neutrals (from the source 12-3, the downstream 12-3, and the 12-2 out) are wirenutted together, as are the grounds.
My 1st question: can I put the orphaned receptacle on the 2nd brance of this circuit? I know code requires 2 20A circuits for countertop appliances, and I have those. Putting this receptacle would be bringing a 3rd 20A circuit into the kitchen. Having met code already, is it okay to have a kitchen receptacle on a circuit that is shared with outside devices?
My 2nd question is this: because this outlet will be in the kitchen, I want it to be GFCI protected. Can I install a GFCI receptacle on a circuit with a shared neutral? If I can, my plan would be to put the live red into the hot line, the black into the hot load, and then create two neutral pigtails to go into the neutral bundle. And, naturally, I'd pigtail a ground into the all the other grounds.
Third question: if I cannot put a GFCI receptacle on this circuit, what are my options for getting GF protection? I assume I can always replace the breakers (currently double pole) with a GFCI double pole. Any other options?
Any input and feedback would be greatly appreciated. And again: apologies for the loooooooong post.