How many years does Romex last?

Romex, or NM-B non-metallic sheathed cable installed correctly inside a dry wall cavity or attic, can easily last 50 to 70 years or even longer, and in many homes original Romex from the 1960s is still in service today. The copper conductors themselves do not degrade with age if they are not overloaded, and the PVC thermoplastic insulation is very stable when protected from UV light, excessive heat, and physical damage. The average life expectancy depends heavily on installation conditions. In a cool, dry, undisturbed interior wall with proper staple support and no rodent damage, it can last the lifetime of the house. Factors that shorten its life include overheating from overloading circuits beyond 80 percent of rated amperage, loose connections that cause arcing, rodent chewing, exposure to extreme attic heat above 130 degrees Fahrenheit for decades, UV exposure in exposed locations, and physical damage from nails, drywall screws, or improper stapling that pinches the jacket. The older NM cable without a ground wire from before the 1960s and the early aluminum Romex from the late 1960s and 1970s have shorter practical lifespans and are often recommended for replacement due to safety concerns. Modern copper NM-B with 90-degree rated conductors should be inspected after 40 years but does not have a mandated replacement interval if it shows no signs of brittleness, cracking, or discoloration.