How to Troubleshoot Obsolete Knob and Tube Wiring

What is Knob and Tube Wiring?

Knob and tube (K&T) wiring was an early standardized method of electrical wiring used in buildings in the United States from about 1880 to the 1940s. It consisted of single insulated copper conductors run within wall cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported on nailed-down porcelain knob insulators.

This old wiring system has largely been replaced due to inadequacies compared to modern wiring methods. However, some homes still contain functional knob and tube wiring. This can present safety issues and difficulties when remodeling or upgrading electrical systems. Understanding how to evaluate and troubleshoot knob and tube wiring is important for homeowners and electricians dealing with older homes.

Hazards and Limitations of Knob and Tube Wiring

There are several hazards and limitations associated with knob and tube wiring that make it obsolete compared to modern electrical systems:

Evaluating and Troubleshooting Knob and Tube Wiring

When dealing with a home with knob and tube wiring, evaluation and troubleshooting is critical before undertaking any upgrades or changes. Key steps include:

Visual Inspection

Check Circuits and Fuses

Load Testing

Check Grounds

Consider Repairs vs. Replacement

Safe Approaches to Upgrading Electrical with Knob and Tube

When upgrading electrical service in a home with knob and tube wiring, extra care must be taken:

Never Overload Existing Circuits

Do Not Conceal Existing Wiring

Add New Circuits Properly

Replace Dangerous Wiring Before Covering

Hire a Licensed Electrician

Options for Replacing Knob and Tube Wiring

Full Rewiring

Partial Rewiring


Capping and Abandoning

Replacing obsolete knob and tube wiring requires evaluating the existing system, addressing any hazards, and often rewiring all or part of the home to create a safer, more robust electrical system. Hiring a professional electrician is highly recommended. With the right approach, the risks of knob and tube wiring can be successfully eliminated.