Yes 1/0 wire can be used for both ungrounded( hot wires) and the grounded conductor (neutral).
No, one is a "HOT" wire.
Yes there is absolutely no problem with grounding two wires to one bolt. Just make sure they both ground wires and one isn't a power wire, you will end up blowing a fuse if you do.
check ground wires under both doors
No, you do not need two ground wires if you split an outlet. The ground wire can be shared between the two new outlets, as long as it is connected properly to both of them. Make sure the ground wire is securely connected to both outlets to ensure proper grounding for safety.
To wire a bathroom fan and light to operate on the same switch, you will need to connect the hot wires from both the fan and light to the hot wire coming from the switch. Then, connect the neutral wires from both the fan and light to the neutral wire coming from the switch. Finally, connect the ground wires from both the fan and light to the ground wire coming from the switch. This will allow you to control both the fan and light with a single switch.
Purchase a ground rod from an electrical supply. Drive it into the ground just outside where your service is located. Install a ground cable from the neutral bar in the fuse box to the ground rod and clamp both ends. Voila, you have done it!
Connect the black wire from the switch to the black wires of both lights. Connect the white wires together. Connect the red wire, if used for the motion sensor, to the black wires on the lights. Connect all ground wires together and to the ground terminal on the switch. Make sure to turn off power before connecting any wires for safety.
You will have to check to make sure. Normally, with 4 wires, the black and red are both power for 220. White for neutral and bare for ground. If you are only using one leg of it, you would use the black, white, bare ones and cap the red one. Someone may have used the 4 strand because they had it or 220 was planned but not done or both the red and black are hot. You should be able to tell in the panel. Do the red and black both connect to separate breakers or to one or is the red not connected?
In an electrical panel, the neutral and ground wires are connected to the same bus bar to provide a path for electricity to flow back to the source and to ground any excess electricity for safety. The neutral wire carries current back to the source, while the ground wire is a safety measure to prevent electric shock. Connecting them to the same bus bar ensures that both wires have a direct path to return electricity safely.
Inside the computer, the various ground wires are black. Computers use direct current inside. The wiring color differs from AC, where both red and black wires are hot wires, white is neutral, and green or bare is ground. In a computer, the red and yellow wires are positive wires of different voltages.
Chassis is ground (neutral) in a car. The two hot wires are for the radio and the light. Connect the smaller wire to the dash light circuit and the larger wire to the accessory circuit.
Easy rule of thump to follow when dealing with grounds. You can never have too many grounds. The more grounds the better for all systems. If in doubt add the ground.