How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
Can old electrical wiring go bad inside a wall?
Friday, July 13, 2018
Although the cable sheathing and insulation on wiring eventually deteriorates, it takes a long time. The wiring that is currently manufactured is estimated to have an 80 to 100 year lifespan. Original wiring in pre-1940 homes that is knob-and-tube type will definitely have brittle and flaking insulation by now, but most post-war wiring should still be in acceptable shape inside walls.
Older wiring in the attic is a different story, and is more likely to have problems for two reasons:
- The extreme heat in an attic in the summer accelerates the the aging and progressive brittleness of the insulation of wiring manufactured before the 1980s, when the thermal resistance of plastic insulation was increased.
- Also, wiring in an attic can be damaged by people crawling over it to do repairs or home improvements, and storage boxes being pushed back-and-forth across it.
Rodents or squirrels in the attic gnawing on the wires can also be a problem, although we see this issue rarely. But we look for damaged wires, like in the photo below, whenever evidence of animal activity in the attic is found, such as urine stains, fecal pellets, and nesting material.
Because wiring inside a wall is not accessible without tearing out wallboard, it is entombed and protected in place for life. Only an unlucky nail into a stud without the required protective plate over the electric cable crossing point has the potential to damage the wiring. Any electrical shorts or arcing inside a wall are more probable around the connections at the outlet and switch boxes that are accessible to meddling by weekend warrior home-improvers.
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