How to Work With Knob and Tube Wiring

How to Work With Knob and Tube Wiring

What is Knob and Tube Wiring?

Knob and tube 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 type of wiring has largely been replaced with modern electrical cables and conduit due to safety concerns and the difficulties of upgrading knob-and-tube circuits. However, some older homes still have functioning knob-and-tube wiring. As the owner of a home with this type of wiring, it's important to understand how to work with it safely.

Dangers and Challenges of Knob and Tube Wiring

Knob and tube wiring presents several potential risks:

Working with knob and tube wiring requires great caution. Never assume a wire is safe to touch.

Best Practices When Working With Knob and Tube Wiring

If your home has knob and tube wiring that you cannot fully replace at this time, here are some best practices to follow:

Inspect and Test the Wiring

Use Caution During Any Renovations

Do Not Overload Circuits

Consider Upgrading or Replacing Knob and Tube Wiring

With proper precautions, knob and tube wiring can still be used safely in many cases. But be very cautious, and make plans to fully upgrade to modern wiring when possible.

Frequently Asked Questions about Knob and Tube Wiring

Is knob and tube wiring dangerous?

Knob and tube wiring is generally considered more dangerous than modern electrical wiring due to the lack of grounding and risk of insulation damage over time. However, with proper precautions and usage within its electrical capacity, it can often still be used safely.

Can I run a ground wire with knob and tube wiring?

It is possible for an electrician to retrofit grounding wires with knob and tube circuits in some cases. But this may be very labor intensive. A full rewiring is recommended for optimal safety and functionality.

What appliances and devices should not be used on knob and tube wiring?

Avoid large appliances like stoves, air conditioners, electric hot water heaters, or anything else that draws a lot of current. Also do not use sensitive electronics and computers on ungrounded knob and tube circuits due to the risk of damage.

Is insurance more expensive if my home has knob and tube wiring?

Many insurance companies charge higher premiums or refuse to insure homes with knob and tube wiring due to the increased fire risk. Upgrading the electrical system often results in lower insurance rates.

How much does it cost to replace knob and tube wiring?

The cost to completely remove knob and tube wiring and rewire a home with modern NM cable and grounding can range from $8,000 to $15,000 depending on the home's size and accessibility. Upgrading one section or circuit at a time costs considerably less.


Knob and tube wiring requires an abundance of caution. Avoid overloading circuits, carefully inspect insulation, and use wire detectors before doing any structural work. For maximum safety and functionality, make plans to upgrade to modern grounded wiring over time. With proper precautions, knob and tube can still be used in many homes - but be very aware of its risks and limitations. Consulting an experienced electrician is highly recommended when evaluating your options.