How to Find and Fix Dangerous Knob and Tube Wiring in Your Home

Knob and tube wiring was commonly installed in homes built before 1950. While it was suitable for the electrical needs of the time, this old wiring can be dangerous by today's standards. As a homeowner, it's important to be able to identify knob and tube wiring and understand the risks it poses. With some diligence and electrical know-how, I can find and fix any dangerous knob and tube wiring in my home.

What is Knob and Tube Wiring?

Knob and tube wiring consists of single black (hot) and white (neutral) wires that are separated by ceramic knobs and tubes.

This type of wiring had no ground wire and was never intended to handle the electrical loads of modern households.

Key Characteristics of Knob and Tube Wiring

Dangers of Knob and Tube Wiring

While knob and tube wiring has lasted surprisingly long in many homes, it does pose safety risks that I should take seriously.

Fire Hazard

The main danger is fire hazard. The old insulation on knob and tube wires often deteriorates, exposing bare copper conductors. This can lead to short circuits and excessive heat buildup. Fires often start where wires pass through wood studs and joists.

As knob and tube circuits are overloaded over the years, the fire danger goes up. I need to be very careful not to exceed the capacity of these old wires.

Shock Hazard

Exposed conductors can also create a shock hazard. If a bare hot wire makes contact with a grounded metal case like a sink, water pipe or duct work, it could electrify that surface and shock anyone who touches it.

Lack of Grounding

Proper grounding is essential for safety, but knob and tube wiring has no ground wires. Ungrounded wires and outlets can lead to shocks or damage to modern appliances and electronics.

Insurance Issues

Many insurance companies will not issue new policies on homes with knob and tube wiring due to the fire risks. Those that do often charge a higher premium or require that the wiring be replaced.

Locating Knob and Tube Wiring

Finding all the existing knob and tube wiring is the essential first step before I can fix or replace it. Here are the best ways to locate it:

Attic and Basement

I need to thoroughly inspect the attic (if accessible) and basement for the distinctive ceramic knobs, tubes and fabric-insulated wires. I may need to move a lot of insulation and stored items to gain full access.

Behind Walls

Removing wall plate covers on outlets and switches can reveal old wiring. I need to check inside cabinets and chase walls as well.

Wiring Details

I should trace wires from outlets and fixtures back as far as possible to find splices, routes into walls, and connections to the electrical panel.

Labels and Documentation

If the previous homeowner left behind a diagram of wiring runs, it can provide valuable clues about the location of knob and tube circuits.

Evaluating Safety and Function

Once I've mapped out all the existing knob and tube wiring, I need to thoroughly evaluate its current safety and performance.

Visual Inspection

I will closely examine the full length of wires for signs of:

Thermal imaging can also help identify hot spots.

Wiring Capacity

I need to measure wire gauges and circuit loads to ensure knob and tube circuits are not overloaded beyond original specifications. This requires meticulous load calculations for all outlets and fixtures.

Electrical Testing

Using a multimeter, I can test for:

Checking for ground faults and arc faults also provides useful safety information.

Repairing or Replacing Knob and Tube Wiring

Once I've identified any risky or deficient knob and tube wiring in my home, I have two options - repair it or replace it completely.

Repairing Knob and Tube Wiring

If the original conductors are in good condition, I may be able to just:

However, this is generally a short term fix.

Replacing Knob and Tube Wiring

For a permanent solution, I will likely need to:

Replacing knob and tube wiring is a major project, but well worth it for safety. I should hire a licensed electrician if I am not 100% confident in my electrical skills.

Protecting My Home with Safe Electrical

Finding and remediating any remaining knob and tube wiring gives me great peace of mind. By taking the right precautions, I can protect my family from fire and shock hazards. Investing in modern, code-compliant electrical wiring allows me to light up my home with safety.