The wire size depends on how much current it will conduct.
In residential wiring the white wire is neutral on the 120 volt circuits. On a 3way circuit the red is the traveler and the white is neutral. On a 240 volt 3 wire connection the white & black are hot. On a 240 volt 4 wire connection the black and red are hot and the white is neutral.
Depends on the size of the circuit which you did not list.
Because the white wire on a 120 volt circuit is the neutral wire that is connected to the silver screw on outlets and switches. It is connected to the neutral bar in the service panel.
battery, wire, and light bulb
Use 8 gauge wire.
If it is a 110 volt light it can safely run on a 20 amp circuit with AWG # 12 wire.
No, you cannot wire a 120 volt ballast to a 347 volt circuit. The ballast is designed to operate at a specific voltage, in this case 120 volts, and connecting it to a higher voltage circuit like 347 volts can damage the ballast and pose a safety hazard. It is important to match the voltage rating of the ballast to the circuit it will be connected to.
# 3 gauge
In the US of A, it's supposed to be black.
When connecting a volt meter to a light bulb to measure the voltage of the light bulb, run a third wire from where the wire enters the bulb to one terminal of the voltmeter and a fourth wire from the other side of the bulb to the other terminal of the voltmeter.
AWG # 10 wire on 30 amp circuit.
No !
A ground (earth) wire is needed in not just a light circuit but in all circuits that are now installed.
To wire a 240-volt light fixture, you'll need to ensure you have a dedicated circuit with a 240-volt power supply. You will connect the fixture's hot wire to one of the hot wires from the circuit, the neutral wire to the neutral wire, and the ground wire to the ground wire. It's crucial to follow the manufacturer's instructions and consult a licensed electrician if you're unsure.
A 240-volt circuit typically consists of two hot wires and a ground wire, with no neutral wire. The hot wires each carry 120 volts, while the ground wire is used for safety purposes. In a 240-volt circuit, the hot wires complete a loop by connecting to a load or device that requires the higher voltage to operate.
test light or volt meter