How to Replace Ancient 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 Canada and the United States from about 1880 to the 1940s. It consists of single insulated copper conductors running within walls and ceilings, supported by nailed-down porcelain knobs and tubes.

The wiring gets its name from the knobs that hold the wires away from framing, and the tubes that the wires pass through where they enter boxes or pass through framing members. This type of wiring has largely been replaced by newer systems with cables and conduits owing to safety concerns and the need for more capacity to serve today's more electricty-hungry homes and devices.

Dangers of Knob and Tube Wiring

There are several dangers associated with knob and tube wiring that make it important to replace:

• Fire hazard - The insulation on old knob and tube wiring becomes brittle and cracks over time, exposing the copper wire inside. This can allow wires to short circuit and overheat, potentially causing fires.

• Insufficient grounding - Knob and tube systems typically lack a grounding conductor. This makes them more susceptible to electrical shocks and fire hazards.

• Overloading - The wiring is not rated to handle the electricity demands of modern appliances and devices. Overloaded circuits can overheat and fail.

• Unsafe splices - Splicing of circuits is often done improperly in knob and tube systems, creating potential points of failure.

• Insurance issues - Many insurance companies will not cover houses with knob and tube wiring, or charge substantially higher premiums.

Why Replace Knob and Tube Wiring?

Here are the key reasons you should replace knob and tube wiring in your home:

• Safety - As outlined above, knob and tube wiring poses serious fire and shock hazards that can put your home and family at risk. Replacing it greatly improves electrical safety.

• Reliability - The old wiring cannot handle the electricity needs of modern life. Replacing it will provide more robust and reliable power throughout your home.

• Resale value - Homes with knob and tube wiring can be difficult to sell and have reduced values. Replacing it can significantly improve resale potential.

• Insurance - You may need to replace knob and tube wiring to get homeowners insurance coverage on your house.

• Expand circuits - Upgrading allows you to cost-effectively expand circuits to add lighting, appliances, and outlets throughout your home.

• Peace of mind - Eliminating the safety hazards of old wiring lets you relax knowing your home's electrical system is safe and meets modern standards.

Replacing Knob and Tube Wiring

Replacing knob and tube wiring completely requires rewiring the entire home with modern wiring methods. This involves:

Hiring an Electrician

• Due to complexity and safety issues, only a licensed electrician should do knob and tube replacement.

• Get quotes from at least 3 electricians before choosing one.

• Verify they have experience and are insured to work on knob and tube replacement.

Wiring Method

• New wiring is typically run through walls and ceilings through protective conduit or armored cable.

• Common replacement methods include NM cable (Romex), MC cable, or EMT conduit with THHN conductors.

Running New Circuits

• The electrician will run all new wiring from the main panel throughout the house, installing new receptacles, switches and fixtures.

• Walls and ceilings may need to be opened up to run wiring, then patched.

• Existing knob and tube will be entirely disconnected and removed.

Electrical Panel

• The main circuit breaker panel may need to be replaced to support added circuits.

• New grounding conductors will be connected.

• All circuits will be properly labeled.

Safety Standards

• All work will meet the National Electrical Code (NEC) and local building codes.

• A permit and inspections are usually required.

Costs

• Costs for a full knob and tube rewire range from $8,000 to $15,000 on average depending on home size and scope of work.

• Get multiple quotes to find the best rate.

Dangers of Partial Replacements

• It's recommended to fully replace knob and tube wiring, not just partial rewiring.

• Leaving any old wiring in place still poses fire and shock risks.

• Old and new wiring systems mixed together can accelerate failures at connection points.

• Partial replacements are often more complicated and costly than a full rewire.

• They may still leave you with insurance issues or an inability to sell the home.

Alternatives to Rewiring

If complete rewiring is not feasible, possible alternatives include:

• Running new wiring just for critical circuits - kitchen, bathrooms, laundry, etc. Leaving knob and tube for lighting and outlets on lower-use circuits.

• Installing GFCI outlets on old wiring to add protection from shocks. Note: Does not resolve fire hazards.

• Running high-voltage extension cords from new wiring to outlets and appliances. Note: Can overload circuits.

• Using plug-in AFCI adapters on old outlets. Provides some fire protection but has limitations.

However, a full rewire is strongly recommended for safety. The alternatives just minimize risk rather than removing it.

Conclusion

• Knob and tube wiring poses serious fire and shock hazards and cannot support modern electricity demand.

• Replacing all of the old wiring with brand new wiring and equipment greatly improves home safety, marketability, insurance rates, and resale value.

• While expensive, a complete rewiring by a qualified electrician is a smart investment in your home's safety and value.

• For budget reasons partial replacements may be considered, but a full rewire should be planned when feasible.