How to Safely Replace Knob and Tube Wiring in Old Homes

How to Safely Replace Knob and Tube Wiring in Old Homes


Replacing knob and tube wiring in old homes can seem like a daunting task, but with proper precautions and planning, it can be done safely. Knob and tube wiring was commonly installed in homes built before 1950 and has largely been phased out due to safety concerns. While not inherently dangerous, knob and tube wiring lacks modern safety features like grounding and can be a fire hazard if damaged or overloaded. With some electrical know-how and help from a licensed electrician when needed, homeowners can upgrade old wiring and gain peace of mind.

Dangers of Knob and Tube Wiring

Knob and tube wiring consists of individual wires that are separated by ceramic knobs and run through wooden tubes or conduits. This type of wiring has the following safety issues:

Replacing knob and tube wiring eliminates these hazards by installing modern, grounded wire with up-to-date safety features.

Planning Your Wiring Replacement Project

Careful planning is required when tackling a full knob and tube rewiring project. Here are some key steps to take:

Consult an Electrician

Have a licensed electrician inspect your existing system for signs of damage, improper modifications, and overload. They can help devise a plan for replacement based on your home's needs.

Check Permit Requirements

Most areas require permits for extensive electrical work like full rewiring. Check with your local building department to ensure proper permits are obtained.

Design the New System

With the electrician, map out the new wiring system including the service panel size, number of circuits needed, and any re-routing required.

Develop a Budget

Factor in costs for the electrician's time, new wiring and panels, materials, permits, and inspections. Rewiring a whole home can easily cost $8,000 to $15,000.

Schedule Work in Phases

Rewiring a home section-by-section makes the process less disruptive. Discuss a phased schedule with your electrician.

Key Safety Tips for the Rewiring Process

When replacing knob and tube wiring, safety should be the top concern. Follow these tips to prevent hazards:

Installing New Grounded Wiring

Once safety preparations are made, the knob and tube wires can be replaced with modern Romex wiring:

Running Cables

Cables should be run through the walls horizontally and vertically between outlets and the service panel. Use cable staples to securely fasten the wiring every 4.5-5 feet along its run.


Where new cables splice into existing wires, use twist-on wire connectors and wrap the connection in electrical tape for a secure join.

Outlets and Switches

Replace outdated two-prong outlets and switches with safe, grounded, three-prong versions. Install safety tamper-resistant outlets in areas where children may be present.


Connect the ground wire in all new cables to the ground bus bar in the main service panel. Additionally, bond the ground wires to metal outlet boxes for extra protection.

Panel Upgrade

If necessary, upgrade the capacity of the main service panel to handle added circuits. Follow permit requirements and have an electrician complete this hazardous task.

Wrapping Up the Project

Once the new wiring system is installed completely, there are a few final steps:

Replacing outdated and potentially dangerous knob and tube wiring requires significant effort and investment. But ultimately, having a modern, grounded wiring system makes your home much safer. By following proper safety precautions and utilizing a licensed electrician when appropriate, the project can be completed successfully.