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Is all cloth wiring dangerous?
Friday, January 31, 2020
Electrical wiring insulation has gone through multiple upgrades over the years, primarily for fire resistance. Wiring up until the mid-20th century was insulated with rubber embedded with cloth, which some electricians call “rag wiring.” The material had two safety problems:
1) The rubber hardens, cracks, and pieces start to break off over time, especially in a hot attic.
2) The cloth-rubber combination has a low thermal resistance and can melt or catch fire when the wires overheat.
Thermoplastic insulation was introduced in the 1950s for wiring, and it has a higher thermal resistance than the cloth-rubber. The cable bundle was still wrapped in cloth and, although the newer insulation is safer, it can be difficult to differentiate from the older wiring. It’s important to be able to tell the difference, because some insurance companies do not want to write homeowner’s policies on old homes with cloth-rubber insulated wiring because of the fire risk, but consider the thermoplastic insulated wire in a cloth-sheathed cable acceptable. Others consider cloth-covered wiring okay as long as the cloth/rubber insulation is not deteriorated.
Here’s some more examples below.
Newer non-metallic cable has a nylon/plastic sheathing and an example is at the yellow arrow above. Also, since 1986, the formulation for the thermal resistance of the plastic insulation was improved to withstand a temperature of 90º C (equivalent to 194º F).
The older cloth-sheathed cable, although it has thermoplastic insulation on the individual wires, deteriorates and can fray over time in an attic, like in the photo below.
So, if an inspector tells you that you have cloth wiring, be sure to get clarification as to whether it is cloth/rubber insulation (often bad for insurance) or cloth-sheathed cable with older thermoplastic insulation (not great, but more acceptable).
Also, if you have wiring that looks like this in the attic or crawl space of your home, it’s called “knob-and-tube,” and the insurance company will definitely want it replaced. See our blog posts What is "knob and tube" wiring? and What is rag wiring? to learn more.
If your old wiring is deemed unacceptable by an insurance company based on a home inspector’s four-point inspection report, you still have the option to hire an electrician to report on their professional opinion of the condtion of the wiring—which may sway the underwriter to drop the objection and offer to insure the property without replacement of the wiring—or not.
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