Copper wire is used for electrical connections between the breaker box and the electrical outlets and switches in your home. A visual inspection will help you determine if a copper wire goes bad. In addition, the use of a multimeter or ohmmeter will help you determine if a copper wire went bad. A bad copper wire is a fire hazard and requires immediate replacement.
Inspect the plastic insulation on the outside of the wire. Look for black spots (if the wire insulation is not black), melted spots in the insulation or cracks in the insulation. If you locate any of these things, the wire is defective.
Place your multimeter or ohmmeter onto the ohm setting.
Place the red lead wire from the multimeter onto one end of the wire you want to test. The lead must touch the copper of the wire. Place the black lead on the other end of the wire. The lead must touch the copper part of the wire.
Inspect the digital or meter readout on the multimeter. If it reads anything higher than zero, then the wire has conductivity and works properly. If it reads zero, the wire is defective.
When testing a wire with a multimeter. Always remove power from the wire and disconnect it from the circuit. This will avoid the possibility of electric shock and damaging the multimeter.