Assuming you are working with 120v, you need #4 AWG copper conductors.
12 gauge underground wire or if you think you will ever add any devices to this circuit use 10 gauge.
A circuit breaker does not have a wire fuse in it.
Yes, you install a GFCI on a 2 wire circuit.
An iron nail can replace a short length of wire in a circuit if the points of contact of the nail to the rest of the circuit have no rust or corrosion and good connection can be made. Using solder to join the nail to the circuit can help make a good connection. However, if this is for a scientifically controlled experiment fine as long as its very low voltage. If you are considering high voltage . DO NOT ATTEMPT IT. Its extremely dangerous
No. In a 20 amp circuit all wire has to be 12 AWG or larger.
A 2C #14 will be suffice but it should be the only device on the circuit. This is known as a dedicated circuit.
copper wire
8 ga
12 gauge underground wire or if you think you will ever add any devices to this circuit use 10 gauge.
Cannot answer this question. Will need to know the voltage and amperage of the circuit. Also need to know the application i.e. is it a lighting circuit or a motor circuit?
It means the Left Side Radiator Primary Crash Sensor Feed/Return Circuit Open. Broken wire, a disconnected wire, or something where the circuit path is not making a good connection.
An engineered set of blueprints will have all of the pertinent information about circuit loading and circuit numbers and panel balancing already calculated. If there is no wiring schedule on the print then you refer to the electrical code book and abide by the regulations that are set out for circuit loading and the amount of devices that can be connected to that circuit. Single family dwelling: multiply the number of square feet by 3. So a 2500 sq ft home times 3 = 7500 watts. Divide that number by 1500 for #14 wire circuits or 2000 for #12 wire circuits. 7500 divided by 1500 = 5 #14 wire circuits or if divided by 2000 + 3.75 or 4 #12 wire circuits. This would be for the lighting load and general use receptacles through out the home. I always lay my circuits out where a circuit only covers 500 sq ft of the dwelling.
A GFCI can not be used on a three wire branch circuit. It has to be on a single two wire circuit.
The wire comes from the installer or manufacturer of the circuit.
A circuit breaker does not have a wire fuse in it.
In residential wiring applications the most used is 14 gauge wire for light switches as long as the circuit breaker or the fuse is 15A. If your lighting circuit is on a 20A fuse/circuit breaker then you need to use 12 gauge wire
If this question is asking about voltage drop, to size a wire, a voltage is needed.