What Causes Wiring Insulation to Become Brittle?

What Causes Wiring Insulation to Become Brittle?

Wiring insulation is the plastic or rubber jacket that surrounds the conductor and prevents it from contacting other wires, surfaces, or people. When insulation becomes brittle, it cracks, flakes, or disintegrates — exposing the energized conductor and creating shock and fire hazards. Brittle insulation is one of the most common findings during electrical inspections of older homes.

Primary Causes

• Age and thermal degradation: All insulation materials degrade over time. Rubber insulation used before the 1960s becomes brittle and crumbles, especially where wiring passes through metal conduit or around sharp edges. Modern PVC insulation lasts longer but still degrades over decades, particularly in hot locations like attics
• Heat exposure: Wiring run near heat sources — furnaces, water heaters, recessed lighting, or in attics with inadequate ventilation — degrades faster. Sustained elevated temperature accelerates the chemical breakdown of the insulation polymer
• Overloading: Running a circuit above its ampacity causes the conductor to heat beyond the insulation’s rated temperature. Even brief overloads stress insulation; repeated overloads cause cumulative degradation
• Rodent damage: Rodents chew through insulation deliberately — it is a common attic and crawlspace finding. Chewed insulation exposes bare conductors against wood framing
• Chemical exposure: Insulation near oils, solvents, or cleaning chemicals in garages and utility areas degrades faster than insulation in conditioned living spaces

What to Do

Brittle or damaged insulation cannot be repaired with electrical tape — it must be replaced. EZSMART inspects wiring conditions in attics, crawlspaces, and accessible junction boxes across Ontario. If your home has older wiring or a history of rodent activity, contact us to assess the insulation condition and replace affected wiring before it becomes a hazard.

Amir Azimipour

Electrician Since 2008 Journeyman Electrician Designated Master Electrician at EZSMART Corp