If you mean a bare copper wire, that is the "ground" wire.
Mainly copper for the wire, pvc for the insulation.
copper is used because it is an electrical conductor which makes the electricity flow around the whole circuit.
The main electrical ground wire is sized to the service and is non insulted bare copper. Branch circuit grounds are green in conduit installations and bare copper again in house wiring cables.
Because the metal Copper is a very good conductor - of both electricity and heat - copper wire can be used to carry an electric current in an electric circuit. The electric current consists of a flow of electrons.
The wire comes from the installer or manufacturer of the circuit.
Copper!
The wire in a circuit helps to pass power to the electrical appliances.
A #3 copper conductor with an insulation factor of 90 degrees C is rated for 105 amps.
Electrons are the predominant carriers of charge in copper wire.
Current will cease to flow in a series electrical circuit.
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electrical wire