How long does electrical wiring last?

The metal in electrical wire should last 100 years or more, with the exception of aluminum wiring, which requires application of an anti-oxidant paste at connection points where the bare metal is exposed to air to ensure a long life. But the insulation around the metal will deteriorate sooner, with a lifespan of between 50 and 80 years and an average of 70 years. So insulation is the determining factor in wiring life expectancy. 

    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 even 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?
  
    Here’s a graph that compares the life expectancy of wiring to other electrical components in a home.
    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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Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
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Here’s links to a collection of our other blog posts about ELECTRICAL WIRING:

• Which house appliances need a dedicated electrical circuit?

• Can a short circuit cause a high electric bill?

• What is the maximum spacing requirement for securing NM-cable (nonmetallic-sheathed cable)?

• Is it alright to just put wire nuts on the end of unused or abandoned NM-cable or wiring?

• What causes copper wires to turn green or black in an electric panel?  

• What are typical aluminum service entrance wire/cable sizes for the electrical service to a house?

• Why is it unsafe to bond neutral and ground wiring at subpanels?

• Should I get a lightning rod system to protect my house?

• Why is a strain relief clamp necessary for the cord connection to some electric appliances?  

• Does a wire nut connection need to be wrapped with electrical tape?

• What is the minimum clearance of overhead electric service drop wires above a house roof?

• What are the requirements for NM-cables entering an electric panel box? 

• What is the color code for NM cable (Romex®) sheathing?

• Why is undersize electric wiring in a house dangerous? 

• What causes flickering or blinking lights in a house?

• Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

• How can I find out the size of the electric service to a house?

• What is a ground wire? 

• I heard that aluminum wiring is bad. How do you check for aluminum wiring?  

• What is "knob and tube" wiring?  

• What is the code requirement for receptacle outlets in a closet?

    Visit our LIFE EXPECTANCY and ELECTRICAL pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

NOTE: These life expectancies are based on data provided by InterNACHI, NAHB, FannieMae, and our own professional experience. Because of the numerous variables that can affect a lifespan, they should be used as rough guidelines only, and not relied upon as a warranty or guarantee of future performance.