How to Test and Repair Aging Knob-and-Tube Wiring

How to Test and Repair Aging Knob-and-Tube Wiring

What is Knob-and-Tube Wiring?

Knob-and-tube wiring was commonly installed in homes built before 1930. It consists of individual wires that are run through the wall cavities, with ceramic knobs used to hold the wires in place and air as the insulator.

The wires are either single conductors with a cloth or rubber insulation or two conductors twisted together with fabric insulation. They are often connected to devices like switches and outlets with soldered joints or wrap-around connections.

Key characteristics of knob-and-tube wiring:

While knob-and-tube wiring was suitable for the first half of the 20th century, it lacks safety features that are standard in modern electrical systems. Proper testing and repairs are crucial for ensuring this old wiring is still safe to use.

Dangers of Old Knob-and-Tube Wiring

Knob-and-tube wiring that has aged can pose a few key risks:

I regularly test and inspect older electrical systems to identify any signs of deterioration or unsafe conditions. Protecting my customers from fire and shock hazards is my top priority.

Testing Knob-and-Tube Wiring

I use a few methods to thoroughly test knob-and-tube wiring and check for any problems:

Visual Inspection

Continuity Testing

Load Testing

Infrared Scanning

Testing is essential for finding issues within walls that are not visible. I assess the entire system thoroughly from the main panel to outlets.

Evaluating Problems with Knob-and-Tube Wiring

Based on the testing results, I evaluate any issues found and determine recommended actions:

I thoroughly explain any issues found and risks identified so my customers can make informed decisions about repairs. The goal is to keep their family and home safe.

Repairing or Replacing Knob-and-Tube Wiring

For minor issues, I may recommend targeted repairs:

However, many homes with knob-and-tube wiring require:

Full Rewiring

This involves:

Rewiring maintains the existing outlet locations but provides a modern, safer electrical system.

Circuit Breaker Panel Upgrade

An updated panel provides:

I follow best practices and local codes when repairing or replacing old wiring. Safety is always the top priority.

Maintaining Old Electrical Systems

For homes still using knob-and-tube wiring, I recommend:

With routine inspections and proper maintenance, knob-and-tube wiring can still be used safely in many homes. But upgrades provide much greater safety margins.


As homes age, thorough inspection and testing helps identify risks with old knob-and-tube wiring. Targeted repairs can improve safety, but rewiring may be required in many cases. With the right approach, I can keep my customers' homes and families protected, whether repairing or replacing their aging electrical systems.