I am replacing two light switches in my bathroom. One controls the light above the sink and the other controls the fan in the ceiling. When I took the old switches out, I saw that the three neutrals were connected together. The three grounds were connected together. One black was connected to a switch, the other black was connected to the other switch, and the third was pigtailed to both switches. My question is on the grounding wires coming from the supply that are connected together. How should I ground the switches themselves? The box is a plastic box.
All the ground wires in a box should be connected together, so add a pigtail from each switch to the ground wire nut, and connect them all together. If this gets to be a lot of wires (sounds like 3 cables and 2 switches, so 5 total) it may be easier to use a push-in connector instead:
or for 6 conductors:
I'm assuming your switches are wired like the ones I have in my house, at least it sounds similar. I'm guessing your ground wires are just crimped into a bundle at the back of the box and adding a wire to that bundle will require the crimp to be cut off (at least they are crimped inside the box, some of mine were pulled out the back of the box and then crimped, making grounding new switches impossible).
You will need to cut of the crimp and a new copper wire for a pig tail. Make the wire long enough to attach to both switces (like the black wire that is there). Wire cap the 4 ground wires together and you are ready to go.