How to Replace Old Knob and Tube Wiring

What is Knob and Tube Wiring?

Knob and tube wiring was commonly installed in homes built before 1950. It consists of individual hot and neutral wires that are separated from each other, rather than bundled together like modern electrical cables.

The hot and neutral wires are supported by ceramic knobs attached to framing members, and where wires cross, they pass through porcelain tubes. This air space between the wires provided insulation at the time.

While knob and tube wiring was suitable for the lower electrical loads of the past, it is considered outdated and potentially unsafe by today's standards. Common issues include:

• Insulation breakdown from age, exposing bare conductors
• Overloading from modern appliances and electronics
• Fire hazard from arcing due to loose connections
• Lack of grounding for fault protection

Why Replace Knob and Tube Wiring?

There are several compelling reasons to replace knob and tube wiring:

Safety

The biggest concern is fire risk. Degraded insulation can allow wires to overheat, ignite nearby combustible materials, and cause electrical fires. Properly installed modern wiring is inherently safer.

Reliability

Loose connections in old wiring lead to power flickering and outages. New wiring will provide steady, dependable power throughout the home.

Expandability

Knob and tube circuits are often inadequately sized for today's larger homes and modern loads. Replacing opens up more options to add circuits and outlets.

Resale Value

Homes with knob and tube wiring can be difficult to insure and finance. Replacing it can increase resale value substantially.

Peace of Mind

Eliminating the worries over safety, reliability, and insurability provides great peace of mind. Knowing your home's electrical system is safe and robust is very comforting.

Evaluating Your Existing Wiring

Before undertaking replacement, it helps to thoroughly evaluate the existing knob and tube wiring:

• Locations - Note where wiring is run, including inside walls, under floors, and in attic.

• Condition - Inspect for cracked or frayed insulation and loose connections.

• Load - Assess if circuits are overloaded by counting fixtures and outlets.

• Coverage - Check if wiring runs to all parts of house and if additional circuits are needed.

• Grounding - Verify that system has no grounding conductors.

Documenting this information will help plan the new wiring system. Professional electricians can perform more thorough assessments if needed.

Choosing a Replacement Method

There are a couple options to consider when replacing knob and tube wiring:

New Wiring Throughout

This involves pulling all-new wires through the house. It is the most thorough option but also the most time consuming and costly. However, it may be required by local regulations.

Pigtailing

The existing wires are left in place but disconnected and capped off at junction boxes. New grounded cables are run between these boxes to each outlet and fixture. This saves on labor costs.

Discuss which method makes the most sense for your project with electricians.

Hiring a Licensed Electrician

Replacing knob and tube wiring must be done by a qualified electrician familiar with local codes and safety practices.

Some key points when hiring an electrician:

• Verify their license is up-to-date in your state.

• Check reviews from past customers. Look for electricians with strong reviews and experience with rewiring projects.

• Get multiple quotes to compare costs for the work.

• Confirm they will get permits required by the city.

• Agree on a payment schedule tied to completion of defined phases of the work.

• Get lien waivers to protect yourself if they fail to pay suppliers.

Planning the New Wiring System

The electrician will work with you to design the new wiring system for your home. Considerations include:

• Number and size of breakers in the main panel - typically 200A service for most homes.

• The number and types of circuits needed - lighting, outlets, appliances, etc.

• Wire sizes required for safely handling the electrical loads.

• New receptacle and switch locations based on your needs.

• Any special circuits such as air conditioning or electric vehicle chargers.

• Smoke and carbon monoxide detectors as required by code.

Take the chance to meet future needs and build in capacity for expansion.

Removing Old Wiring

Once a plan is in place, the electrician can start removing the old knob and tube wiring:

• Electrical power is disconnected at the main panel to ensure safety.

• Wiring is accessed by removing wall, floor, and ceiling materials as necessary. This is the most labor intensive part of the job.

• Old wiring is disconnected from outlets and junction boxes, snipped into segments, and the cut ends capped off.

• Existing ceramic knobs and tubes are left in place to minimize damage to building materials.

• Walls and ceilings are patched and refinished after the new wiring is installed.

Proper safety precautions are followed, including wearing eye protection and breathing masks.

Running New Wires

Your electrician will take care to neatly route the new wiring throughout the home:

• Modern NM (nonmetallic) sheathed cable is used for most indoor runs.

• Wires are run through drilled holes in framing and joists, staying clear of contact with edges.

• Exterior-rated UF (underground feeder) cable is used where wiring exits the foundation.

• Junction boxes provide access to connect and splice wires.

• Cables are affixed with staples or plastic straps at regular intervals per code requirements.

• Exposed basement wiring runs through conduit for protection.

Connecting Switches, Outlets, and Fixtures

The electrician will take care of all connections to the new circuits:

• Wires are stripped and connected to receptacles, switches, and fixtures with proper terminations.

• Appropriate wire nuts are used to join and insulate conductors at boxes and splices.

• Grounding connections are made to bond boxes, switches, and fixtures to the grounding system.

• GFCI (ground fault circuit interrupter) outlets are added to required locations for shock protection.

• Light fixtures are hung and properly supported with newly installed boxes.

• Any low-voltage wiring, such as for smart home systems, is also handled at this time.

Wrapping Up the Installation

As the project nears completion, your electrician will take these final steps:

• Insulation is repaired or replaced where removed or damaged during the rewiring.

• Drywall patches are sanded and painted to match existing finishes.

• Crawl spaces and attics are cleaned up from any debris generated during the work.

• At the panel, circuits are labeled clearly on index cards for the breakers.

• Any permits are closed out after inspections approve the new wiring system.

When the installation is complete, you'll gain full use of your newly rewired home!

Maintaining the Electrical System

With your old wiring replaced, be sure to maintain your new electrical system:

• Exercise caution when working around wiring and making any modifications.

• Don't overload circuits - be aware of capacity when adding outlets and equipment.

• Test GFCIs monthly by pressing their "test" buttons to ensure proper function.

• Replace any damaged electrical boxes, outlets, or switches.

• Hire an electrician for any significant repairs, upgrades, or troubleshooting.

Following these tips will keep your new wiring in excellent shape for decades to come! Let me know if you have any other questions!