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.

• • • • • • • • • • • • • • • • • • • • • • • • • • •

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 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?

• Can old electrical wiring go bad inside a wall? 

• What is an open electrical splice?

• What are the most common electrical defects found in a home inspection? 

• What is the life expectancy of electrical wiring in a house? 

• What is an "open junction box"? 

• How dangerous is old electrical wiring? 

• What is a ground wire? 

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

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

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