Damaged or Worn Insulation
Without completely intact insulation, electrical wiring is extremely dangerous. Frayed, cut or burned insulation on any wire is a serious hazard. Also, cable splices should always occur inside an approved junction box.
This is no joke, of course. Stories of DIYers using extension cords for circuit wiring are not apocrypha. It happens, and it’s the equivalent of using a garden hose for water-supply pipes. If you find inappropriate wiring anywhere in your house, assume the worst; it’s time for a complete inspection.
Inspection is the Best Defense
The U. S. Consumer Product Safety Commission recommends an electrical inspection of your home every 10 to 40 years, if you’ve added substantial new loads (such as high-wattage appliances) or if you detect any warning signs of wiring problems. Inspections should be conducted by certified electrician or electrical inspector.