Why is Knob and Tube Dangerous?


  • Learn what Knob and Tube is and how it affects home ownership. 7 common issues with K&T wiring arelisted below. 


    Owning a home is a significant investment and when managed correctly can reap substantial rewards now and in the future.   Home ownership provides stability and security for your family and establishes a connection to your community.  It impacts almost every facet of your life today and is a major factor in future financial plans.

  • Owners of older homes know that maintenance and upkeep are essential to protect your family and investment.   For homes built prior to the 1950s, owners should be aware that their home could contain outdated knob and tube wiring (K&T).  Replacing K&T wiring can help increase the value, safety, and functionality of your home.


    Most K&T systems are over 70 years old.  Waiting for aged wiring to fail is both costly and potentially dangerous.  As any system ages there are increased risks of failure.  Some common issues with K&T wiring are:

    1. Buildings settle over time or alterations have been made that allow the wiring to come in contact with the wood structure.
    2. Increased demand from newer power-hungry electrical devices that were not available when the K&T was installed results in messy tangles of extension cords and power strips as homeowners struggle to use limited outlets.
    3. Additional plug strips or wiring extensions may draw too much power on older K&T circuits, causing them to overheat.
    4. K&T wires are not paired together like modern wires, creating an opportunity for accidental cross-wiring.
    5. K&T wires are not color-coded. This can impose the risk of reversed polarity.  Newer wiring and electrical equipment is designed with polarity to prevent accidental shock.
    6. K&T wiring does not include a ground wire to prevent accidental shock.
    7. The National Electrical Code decided in 1987 that it would not permit insulation contact with knob and tube wiring systems. This leads to complications when homeowners decide to upgrade their insulation.

    Knob and tube wiring entering a basment and connecting to 1960's wiringIn additional to safety concerns, obtaining homeowners insurance is becoming problematic if a home has K&T wiring.  Insurance underwriters view K&T wiring as a claims risk.  Many insurance companies are denying coverage to homes with K&T and some have opted to not renew coverage for existing clients with K&T.  This will cause significant delays and issues during the home selling process and may bring unwelcome notices of cancellation or non-renewal of existing policies.   For those few companies that do offer insurance for homes with K&T wiring, it is often more expensive.  This issue is a trend that will only increase with time as this wiring system becomes more outdated.


  • Strategies for dealing with K&T wiring vary depending on the homeowner’s budget and ability to accept household disruption. While rewiring a home is a large project, it is one that can be accomplished while living in the home. 

    The first step is a comprehensive inspection of the home’s wiring by a qualified and licensed electrician.  Once active K&T wiring has been identified, the homeowner should work with the electrician to develop an approach to upgrading their home’s wiring.  There are three common strategies to remediate K&T.

    For a homeowner who wants or needs to be done with renovations in one shot, a complete house rewire can be scheduled.  This is the best option for people whose home is undergoing renovations or is being prepared for move-in.  It ensures that all K&T wiring is de-energized and no longer poses a safety hazard.

               Wiring added to wall in conduit Wiring added to wall in conduit and patched

  • When the long term plan is to eliminate K&T wiring but a full rewire of the house is not feasible, a core rewire lays the foundation to complete the rewire over time.  A core rewire breaks the project into manageable sections, with the plan being to rewire one room at a time until every section has been updated.

    If rewiring a house is not within a homeowner’s budget, a home can be made safer by adding additional circuits, thus reducing the load on older circuits.  This strategy is most effective when lines are run for electrical needs that were not available when K&T circuits were designed.  An example of this would be to run a new circuit for a window AC unit or a home office.

    Owning a piece of history can be a joy.  Taking steps to address serious maintenance issues, such as an aging electrical system, can and should be done by responsible homeowners to protect your investment and increase your everyday enjoyment of your home.


About The Author

Bill earned a degree in Electrical Engineering and Architecture, then founded Generation 3 Electric in 2000. His father, an electrician, was his inspiration. These days, Bill actively manages his company and enjoys focusing on new technology and marketing.