Knob and tube wiring was commonly installed in homes built before the 1950s. This antiquated wiring system features insulated wires running through porcelain knobs and tubing. While knob and tube wiring was suitable for early 20th century electrical loads, it can be dangerous and insufficient for modern households. Replacing this outdated wiring with modern electrical cables is crucial for safety and expanding electrical capacity. Here's how I tackled replacing the knob and tube wiring in my attic.
Dangers of Knob and Tube Wiring
Knob and tube wiring has multiple safety risks that make replacement urgent:
- Fire hazard - The old, dried out insulation cracks over time, exposing bare wires that can arc and spark. This can easily ignite fires in attic insulation and wood framing.
- Insufficient grounding - Knob and tube wiring lacks a ground wire which is essential for preventing electrocution and fire risks.
- Overloading circuits - The wiring is only designed for low wattage lighting and receptacle loads. Plugging in modern appliances can overload the wires and trip breakers.
- Unsafe splices - Homeowners sometimes try improper DIY fixes like twisting new wire around old knob and tube. This creates fire-prone connections.
I decided the safety of my home necessitated a full knob and tube wiring replacement. Consulting an electrician confirmed this was the right move.
Preparing for the Project
Before starting this wiring project, I took several steps to prepare:
- Turn off power - I shut off all power to the attic at the main electrical panel and verified it was off with a voltage tester. Safety first!
- Install temporary lighting - To illuminate the dark attic, I set up battery powered work lights.
- Map out the wiring - I photographed and labeled the existing wires to document their original routing.
- Purchase supplies - I bought new NM-B wiring, junction boxes, outlets, and other electrical supplies.
- Rent drywall lift - To avoid repairs later, I rented a drywall lift to protect the ceilings.
- Protect house - Drop cloths in the rooms below safeguarded against fallen insulation and dust.
Thorough preparation made the wiring replacement process smoother.
Running New Wiring
With the prep work done, it was time to install the new wiring throughout the attic. Here is the process I followed:
Remove Old Wiring
- First, I detached the knob and tube wires from outlets, junction boxes and other endpoints.
- I left the old wires in place for now to use as a guide for running the new wiring.
- Any unsafe splices between knob and tube and newer wires got removed.
Map Out New Wiring Route
- Using the photos of the original wiring, I mapped out the best route to run the new wires to each light and outlet.
- I planned to bypass the old path in some areas for more direct routing.
- For easier access, I centered wiring paths along joists and rafters where possible.
Run NM-B Cable
- Starting at the outlets, I stapled the new NM-B cable alongside the old wiring paths.
- Where necessary, I deviated from the knob and tube routes to simplify the new wiring.
- I made sure to leave extra slack in the line for easy connections.
- At endpoints, I cut the new wiring to length and prepared the ends.
Connect Wires at Endpoints
- Once the new wiring runs were in place, I stripped and connected the ends.
- The connections followed the photos of the original setup I took earlier.
- I joined all the neutral wires at common neutral bus bars in the junction boxes.
- Likewise, all the ground wires were connected to grounding bus bars.
- Finally, I connected the hot wires to match the original circuit routes.
With the new wiring connected end-to-end, it was ready to be energized.
Removing Old Knob and Tube Wiring
Now that the new wiring system was complete, I could remove the outdated knob and tube:
Take Down Knobs and Tubes
- First, I unscrewed any porcelain knobs from the framing and pulled off the flexible tubing.
- Removing all traces of the old system eliminated confusion over what was live.
- I also pulled out any abandoned knob and tube running to unused endpoints.
Pull Out Wires
- Next, I yanked the old wires out of the walls and ceiling cavities.
- In crowded areas, this took some force and wiggling to extract the wires completely.
- Pulling just a section of wire helped as I could use it as a handle to pull out the rest.
Dispose of System
- Finally, I loaded up the collected knob, tubes, and wiring to be disposed of responsibly.
- Proper disposal finished removing the obsolete electrical system from the home.
- I was left with an attic empty of the dated wiring and ready for insulation.
Eliminating all traces of knob and tube wiring simplified the attic and prepped it for the next stages of the renovation project.
Safety Check and Powering Up New Wiring
As the final step, I thoroughly checked the new wiring system and restored power:
- I verified all connections were tight and insulated properly. Loose connections get hot!
- Next, I tested each run for continuity to confirm no opens or shorts were present.
- With everything checking out, I reconnected the circuits at the main panel.
- Switching breakers back on energized the new wires. I checked for proper function of all lights and outlets.
- Lastly, I had the completed system inspected by the local building department. Their approval gave me peace of mind that the wiring was safe and robust.
With those final checks complete, the knob and tube replacement project was finished! My attic finally had up-to-date, safe electrical wiring ready for any modern loads.