How to Replace Old Knob and Tube Wiring
Replacing old knob and tube wiring in your home is an important upgrade that can improve safety and allow your electrical system to handle modern appliances and electronics. This type of wiring was commonly installed in homes built before the 1940s. While it may have served homes well for decades, knob and tube wiring can present fire and shock hazards if left in place too long.
In this guide, I will walk you step-by-step through the process of replacing knob and tube wiring. We will cover planning the project, gathering supplies, removing old wiring, installing new wiring, connecting circuits, and finishing the job. With proper planning and care, you can upgrade the wiring in your vintage home and gain peace of mind knowing it is safer.
Dangers of Knob and Tube Wiring
Before we get into the how-to, let's review why knob and tube replacement is so important:
Fire hazard - The insulation on old wiring can deteriorate over time, exposing bare wires that could arc and spark. This can ignite surrounding combustible materials.
Insufficient for modern loads - Knob and tube was designed for simple lighting and appliance circuits. It may be overloaded by large appliances like air conditioners, or many devices running simultaneously.
Difficult to service - The wiring running through walls and ceilings is not easily accessed. Faulty splices or damaged spots in the wiring can be hidden from view.
No grounding - Knob and tube has only a hot and neutral wire, no ground. This can lead to shock hazards.
Replacing knob and tube wiring entirely removes these risks from your home. Doing this project yourself can save thousands of dollars compared to hiring an electrician. With proper precautions, you can take on this project DIY.
When dealing with electrical wiring, safety should always be your top priority:
Turn off power at the main breaker panel before working. Verify it is off using a non-contact voltage tester.
Work carefully when removing old wiring to avoid accidental shocks. Snip wires only after confirming they are de-energized.
Wear insulated gloves and long sleeves in case of accidental contact with live wires.
Keep a fire extinguisher and first aid kit handy.
Follow all local electrical and building codes. Consider having an inspector review your work when complete.
Proceeding cautiously will help ensure you and your home stay safe throughout this major wiring project.
Before getting started, you will want to ensure you have all necessary materials on hand:
Wire - Use the same gauge size as existing wiring, typically 12 or 14 gauge for 15-20 amp circuits. Purchase enough to replace all wiring.
Junction boxes - To house wire connections. Match existing boxes or use new metal or plastic boxes meeting code.
Cable clamps - To secure cables entering boxes and prevent strain on connections.
Wire nuts - To join wire ends together securely.
Conduit - As required by local code to protect wiring.
Circuit breakers - For any new circuits added during the rewire.
Wire strippers - For removing insulation from wire ends.
Voltage tester - To confirm power is off before working.
Having all supplies ready will prevent delays once you start the rewiring work.
Removing Old Knob and Tube Wiring
With safety gear on and supplies at hand, we can get started:
1. Turn Off Power
Shut off the main breaker and verify power is off with a voltage tester. This may require flipping additional breakers as well.
2. Remove Wiring from Walls and Ceilings
Start by taking down any accessible wiring, removing it from conduits and pulling it out of walls by fishing down from above. Take care not to damage wall and ceiling surfaces.
3. Disconnect Devices
At light fixtures, switches and outlets, disconnect the old wiring. Label wires to note locations and what they power.
4. Remove Knobs, Tubes and Junctions
With wiring disconnected, unscrew any remaining knob and tube hardware. Also remove old junction boxes no longer needed.
5. Pull Wires Out Completely
Finally, pull any remaining wires out from walls and ceilings. Seal up holes as needed for safety.
Work carefully and methodically to get all the old wiring out. This will leave you with a clean slate for the new wiring.
Installing New Wiring
Once the old knob and tube wiring is fully removed, we can install safe, modern wiring:
1. Plan Circuits
Determine where to run each new circuit in the house. Group lighting and outlets appropriately based on rooms and usage.
2. Run Cables
Run new cables through walls and ceilings to each outlet and switch location. Leave extra length for connections. Use conduit where required.
3. Install Junction Boxes
Mount new junction boxes where wiring will be joined. Feed cables into boxes and clamp properly.
4. Make Connections
Join wire ends using twist-on connectors. Follow wiring diagrams created in earlier steps.
5. Secure Wires
Keep wires tidy and secure inside boxes. Allow slack for adjustments. Reinstall switches, outlets, lights.
6. Install Breakers
For any new circuits, install appropriately sized circuit breakers in the main panel.
Follow codes carefully throughout the installation process. Consult local building department with any code questions.
Connecting the New Circuits
With the new cables run throughout the home, we can now join them together into complete circuits:
Match wire colors consistently throughout circuits - hot (black), neutral (white), ground (green/bare).
Ensure hot and neutral wires are not crossed between devices.
Use wire nut twist-on connectors rated for the wire gauge to join ends securely.
Install junction boxes to house connections that cannot be made inside devices.
Use cable clamps at all box openings to avoid strain on wires.
Connect the ground wire to all outlets, switches and metal boxes.
Take the time to make neat, secure connections. This will ensure your new circuits work properly and safely.
Once all new wiring is in place and connected, there are a few final steps to wrap up the project:
Label all circuits clearly in the breaker panel.
Have repairs done to wall and ceiling areas damaged during the rewire.
Caulk around boxes and conduits to seal openings into walls.
Dispose of all old wiring safely. Do not just throw in trash.
Turn power back on and test each circuit. Verify outlets are properly wired.
Consider having work inspected by your local building department.
Celebrate successfully upgrading your home's electrical system!
With diligent attention to detail throughout the process, you can feel confident your home's wiring is now far safer and ready to meet your family's needs.
Do I need to upgrade my electrical service when I rewire?
- Not necessarily. If the existing service provides sufficient amperage for your needs, you can reuse it. But upgrading the service can allow you to add more circuits.
Can I leave some old wiring in place?
- It is best practice to replace all of the knob and tube wiring for maximum safety. Leaving some in place still poses a potential hazard.
Is rewiring something a DIYer can take on?
- With proper precautions, the average handy homeowner can complete a rewire themselves. But consider hiring an electrician if you are unsure about any part of the process.
Does homeowners insurance cover electrical fires related to old wiring?
- It may, but coverage would need to be verified with your specific policy. Insurance providers often require upgrades to minimum safety standards.
How much does a full rewire cost?
- For a typical single family home, expect a DIY rewire to cost $2,000-$4,000 in materials. Hiring an electrician averages $8,000-$15,000 for the complete job.
While rewiring an entire home is a major undertaking, it is a project an ambitious DIYer can certainly take on. With careful planning, safety precautions, and attention to detail, you can eliminate the dangers of knob and tube wiring. Your home will benefit from safer, modern wiring supporting today's electrical needs.