A wire may have a nick or small area where the metal wire is exposed, or has frayed insulation that is falling off or that is damaged from over-heating.
Nicked insulation is often caused by a wire being pulled across the sharp edge of a metal conduit or box, when being installed. When this is discovered, many electricians will merely tape over the area with electrical tape so that there will not be any metal wire contact with another piece of metal wiring, metal box or metal conduit. Some electricians will replace the damaged section of the wiring.
Rodent chewing on the insulation
Rodents such as mice and squirrels may chew through a wires’ insulation exposing the bare metal wire. These areas should be repaired and a rodent control program put in place to prevent future damage.
Frayed or deteriorated insulation
Older homes may have wires with deteriorated or damaged insulation. Frayed or damaged insulation on electrical wires is a safety concern and should be addressed. Homes, with older electrical wiring in them, such as knob and tube wiring or rubber insulated wires covered with a cloth fabric or metal sheeting, are more subject to having deteriorated or damaged insulation. Sometimes the wire has a black rubber insulation that looks like it is covered in a straw like material. Heat and/or age is the basic cause for damage to occur.
Insulation damaged because of heat
In addition to age, overloading of a circuit may cause damage or deterioration to a wire. The overloading creates heat, and it is the heat that causes the damage to the wires insulation.
Repairing of frayed or damaged insulation
Electricians can do this quiet easily and rapidly, and it is wise to fix these areas. Usually they are not big areas.
Note – that UL does not list electrical tape as sheathing for electrical wire.
Who to consult? An electrician or qualified handyman.
When the frayed areas are small, usually a qualified handyman or electrician can make the repairs. Should there be a need to replace all of the wiring, which is seldom the case, then an electrician is best suited.