Knob and tube wiring was commonly installed in homes built before the 1940s. While it was suitable for the electrical needs at the time, this old wiring can be dangerous by today's standards. Replacing knob and tube wiring with modern electrical wiring improves safety and allows your home's electrical system to support more electricity use. Here is how I safely replaced the knob and tube wiring in my home.
Understanding 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. It lacks a ground wire which is essential for safely handling electrical faults. Other drawbacks include:
- Insulation - The wiring is wrapped in cloth and rubber which degrades over time. This leads to exposed conductors and shorts.
- Capacity - Knob and tube wiring is only designed to handle up to 60 amps. Modern homes require 100 amps or more.
- Circuit Protection - Early systems lacked circuit breakers and relied on primitive fuses.
These factors make knob and tube wiring obsolete and hazardous in modern homes.
Dangers of Knob and Tube Wiring
Knob and tube wiring poses several serious risks including:
- Fire hazard - Degraded insulation can lead to electrical arcing and sparks. This can ignite flammable materials in walls and attics.
- Shocks and electrocution - Lack of a ground wire increases the odds of getting shocked. Loose connections can also energize metal surfaces like appliances and plumbing.
- Damage to electronics - Surges can fry delicate electronics like TVs, computers, and smart devices.
- Inability to support updates - It's often impossible to safely add new lighting, appliances, and electrical outlets.
These dangers underscore the importance of replacing old knob and tube wiring.
Signs You Still Have Knob and Tube Wiring
It's not always obvious if a home still contains original knob and tube wiring. Here are some signs to look for:
- Ceramic knobs, tubes, and cloth-wrapped wires inside walls or attics
- Two-prong outlets without a ground pin
- Frequent tripped breakers or blown fuses
- Discolored or warm outlet covers
- Odd-shaped wall cavities concealing the wiring
- Lights dimming when other devices turn on
Finding any of these in a pre-WWII home indicates potential knob and tube wiring. Consulting an electrician can verify if replacement is needed.
Finding a Qualified Electrician
Replacing home wiring is complex and potentially dangerous. It's essential to hire a licensed and insured electrician. When looking for a professional, make sure they:
- Have several years of experience specifically with electrical rewiring projects
- Carry proper licenses for your state and locality
- Have strong reviews and referrals from past customers
- Provide a detailed plan for the project including costs
- Use modern materials that meet electrical codes
Obtain quotes from multiple electricians before selecting one. This ensures you choose someone qualified at a fair price.
Creating a Rewiring Plan
Before work begins, the electrician should inspect the home and create a rewiring plan. This will determine:
- Scope - Which circuits and areas need new wiring. A full rewire is best but partial updates may suffice.
- Rerouting - How to run new wiring through walls, attics, and basements.
- Removal - Whether to completely remove old wiring or abandon it in place.
- Electrical panel - If the main panel needs upgraded to support additional capacity.
- Permitting - Whether a permit is required based on local codes.
- Schedule - How long the project will take from start to finish.
Carefully reviewing the plan helps ensure the project stays on time, budget, and avoids any safety oversights.
Safely Isolating Electrical Systems
Before touching any wiring, the power must be completely disconnected at the main electrical panel. This involves:
- Shutting off the main breaker switch which cuts electricity to the entire home.
- Testing outlets with a non-contact voltage detector to verify power is off.
- Leaving the main breaker off for the duration of the project. Never turn it back on early.
- Labelling the panel to prevent accidental activation.
These steps prevent electrocution and make it safe to work on the existing wiring.
Running New Wiring
With the old power turned off, the electrician can safely route new wiring:
- Modern wiring uses plastic-insulated copper wires for hot, neutral, and ground.
- Running the new wiring often involves drilling holes through wall studs and joists.
- Existing knob and tube wires may be removed or simply abandoned in place.
- All work should be neatly installed to electrical code standards.
- New wires terminates at an upgraded main panel located outside the living space.
Careful planning ensures new wiring avoids plumbing, ventilation, and other hazards hidden within walls.
Installing a New Electrical Panel
The project usually includes upgrading the outdated main electrical panel:
- Old fuse boxes are replaced with circuit breaker panels. These provide better surge and overload protection.
- Capacity is increased, often to 200 amps which supports all modern electrical needs.
- Additional circuit breaker slots allow connecting new lighting, outlets, and appliance circuits.
- A main disconnect switch lets you safely cut all power in emergency situations.
- Modern grounding and neutral bus bars improve safety.
Proper panel sizing prevents overload and allows for future expansion.
Important Safety Checks
Before turning the system back on, the electrician should make several vital safety checks:
- Verify all old wiring is fully removed or disconnected from the panel.
- Confirm new neutral and ground wires are correctly connected.
- Ensure circuits are properly labeled in the panel.
- Test for secure connections and correct polarity.
- Check for loose wires, gaps in insulation, or exposed conductors.
- Inspect for tools, debris, flammable materials which could cause hazards.
- Request the city or an inspector verify the work if required by the permit.
Address any issues immediately. Don't restore power until 100% confident it's completely safe.
Restoring Power and Testing
Once ready, the main breaker can be switched on to restore electricity:
- Turn on lights, outlets, and appliances one at a time to check each circuit.
- Test outlets using a 3-prong circuit tester to verify proper wiring.
- Check for blown breakers or faulty GFCI outlets which may indicate a wiring problem.
- Confirm lights are bright and motors start without issue. Dimming or slowness can mean an undersized wire.
- Listen for sizzling or popping sounds which could signal unseen damage or faults.
Contact the electrician immediately if any evidence of improper or hazardous wiring is found.
Why a Rewiring Project Is Worthwhile
While rewiring an entire home is disruptive and expensive, the benefits are well worth it:
- Your home will meet modern safety standards and electrical codes.
- The risk of a fire is drastically reduced.
- You gain peace of mind knowing your home's electrical system is completely safe for your family.
- Additional capacity allows installing bigger appliances and more lighting circuits.
- Electrical bills may decrease thanks to more efficient wiring.
- The home sees a big boost in value for resale.
Though not cheap, a rewiring project is a smart investment that improves safety, comfort, and convenience for decades to come.