What is the life expectancy of electrical wiring in a house?
Saturday, July 28, 2018
Copper wire should last 100 years or more, but the insulation around it will deteriorate sooner and is the determining factor in lifespan. Each era of electrical wiring has a different expected life, and he earliest type still around in a few older houses is knob-and-tube. It was standard up until the early 1940s and, as the name implies, depends on knobs at changes in direction of the wiring and tubes at penetrations of flammable material like wood, along with air space around the wiring for insulation.
Part of the problem with knob and tubing wiring that is still functional in a home is simply it’s age. The insulation is at least 70-years old, brittle, and flaking off. Another problem is the low current-carrying capacity compared to modern wiring, and difficulty in safely splicing K&T with modern NM-cable. Also, all knob and tube wiring systems are “two-wire,” meaning that they do not contain a third wire for grounding, which has been required for residential electrical systems since about 1960. While K&T is now obsolete, and requires replacement when found during a home inspection, it’s worth noting that it was once state-of-the-art technology.
The next type of wiring was insulated with a rubber-like material and embedded fabric, shown in the photo above. It was used up through the 1950s. The insulation has not held up well in hot attics of North Florida, especially in areas near the attic hatch opening where it has been walked on repeatedly or pushed around by stored Christmas decorations. The wiring is at the end of its serviceable life now in most cases, with cracked insulation flaking off the at bends and splayed fabric; however, sometimes it is still in marginally satisfactory condition, with the expectation of replacement very soon.
Plastic wire insulation with good resistance to thermal deterioration followed next in the mid-1950s, and the formulation of the plastic was upgraded in the 1980s for better heat resistance. The newer wiring is expected to have a lifespan of 80 years or more...but only time will tell. See our blog post Can old electrical wiring go bad inside a wall? for more on this.
Many of our customers buying older houses are concerned about the possibility of a fire due to arcing of damaged or deteriorated wiring in the walls or attic. Two options to consider are wiring replacement or installation of AFCI-breakers in the panel for the general household circuits.
AFCI stands for Arc Fault Circuit Interrupter, and an AFCI breaker does double duty: it protects against too much current flowing through the wires, just like a regular breaker, but also recognizes any sparking in wiring, and trips when either problem occurs. We recommend discussing your options with a professional electrician, who can evaluate the current condition of your house wiring and discuss the pros and cons of the two alternatives.
Although old wiring remains the #1 bugaboo for buyers of vintage homes, other older electrical components are more likely to be a fire problem. Also see our blog post Why are old electrical components not always "grandfathered" as acceptable by home inspectors?
Go to our blog post What is the average lifespan of the parts of a house? for rating of other house components. To understand the basis, potential use, and limitations of lifespan ratings, see our blog post ”How accurate are the average life expectancy ratings of home components? Are they actually useful?”
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Here’s links to a collection of our other blog posts about ELECTRICAL WIRING:
How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
for Links to Collections
of Blog Posts