I had the plumber come out and install a garbage disposal where there wasn't one before, but he was unable to do the electrical hook up. Upon close inspection of the electrical set up in the kitchen, there is a 120v circuit wired with 12/2 running in the island/bar where the sink is located that is dedicated to six power outlets, four of which are located above the counter close to the sink (one is GFI of course). These are meant for small appliances. I would like to replace one of these outlets with a wall switch for the disposal, and tie into this circuit at this point to power it. How do I do this without controlling the remaining outlets with the switch?
First, if this is one of the required appliance circuits of NEC 210.52(B)(1) then it is a violation of 210.52(B)(2) to connect the garbage disposal to it.
If you do connect the disposal to the circuit, there is a small risk that you will trip the breaker when you turn it on if there is a 1500 Watt teakettle or griddle being used to make your breakfast.
Here is the simplest way to make it work. The disposer will be GFCI protected. It isn't required to be, but it is easier for me to explain it if we leave it that way.
1. Select the receptacle that you want to replace with a switch. Ideally, you would remove the last receptacle in the assembly; the one that has only a pair of wires coming to it and none going from it to another receptacle.
2. Remove that receptacle. You will now have a white wire, a black wire, and a ground. The white wire will be probably be connected to a silver terminal on an adjacent receptacle. If it is coming from a bunch wire-nutted together that is fine also.
3. Connect the black wire to one of the terminals of the switch.
4. Run a 12/2 from the box to where it will connect to the disposer. Connect the white wire of the new cable to the terminal that the white wire mentioned in (2) is hanging from (after you remove the little white wire) or to the white pigtail if it is not coming from an adjacent receptacle. Connect the black wire from the new cable to the other terminal of the switch. Connect the grounds with a wire nut and run a pigtail ground to the ground terminal on the switch. Mount the switch in the box.
5. Connect the black, white, and ground wires to the corresponding wires/terminals of the disposal.
Variations:
If you don't want to put the switch in the "last receptacle on the circuit" position, you can take any receptacle except the GFCI receptacle and rearrange the connections to make sure all of the receptacles are powered.