How to Replace Hidden Knob-and-Tube Wiring in Your Home

How to Replace Hidden Knob-and-Tube Wiring in Your Home

What is Knob-and-Tube Wiring?

Knob-and-tube wiring was an early standardized method of electrical wiring used in buildings in the United States from about 1880 to the 1940s. It consists of single insulated copper conductors run within wall cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nailed-down porcelain knob insulators.

This old wiring system does not include a ground wire and lacks the protection of conduit or flexible armored cable. While generally considered safe when properly maintained and unmodified, knob-and-tube wiring can present fire and shock hazards due to improper use, age, or modification. For these reasons, insurance companies may not insure houses with knob-and-tube wiring or may require it to be replaced before issuing policies.

Dangers of Knob-and-Tube Wiring

There are several dangers associated with old knob-and-tube wiring:

For these reasons, experts recommend replacing knob-and-tube wiring whenever possible.

Preparing for a Rewiring Project

Replacing knob-and-tube wiring in an older home is a major project that requires planning and preparation:

Step-by-Step Rewiring Process

The basic process for replacing knob-and-tube wiring is:

  1. Shut off power - The main breaker supplying the knob-and-tube circuits must be turned off. Verify power is off with a voltage tester.

  2. Remove old wiring - Carefully remove the old wiring from the attic and walls back to the main panel and junction boxes. Wear proper protective equipment.

  3. Install new boxes - Upgrade any old junction boxes and install new electrical boxes for outlets and switches.

  4. Run new wiring - Route the new armored or NM cables through the walls and ceilings following local code requirements. Staple the cables in place.

  5. Connect devices and lights - Splice in the wiring for all lights, switches, receptacles, appliances, etc. Follow diagrams carefully.

  6. Connect new wiring to panel - Securely terminate the new wiring in the main panel with cable clamps and matching breakers.

  7. Install plaster/drywall - Patch walls, ceilings, etc. affected by the rewiring. Apply plaster or drywall compound for a smooth finish.

  8. Schedule inspections - Have the completed work inspected and approved by the local building department. Correct any code violations.

  9. Restore power - Once approved, restore electricity to the new wiring from the main panel. Test all circuits thoroughly.

Replacing old knob-and-tube wiring requires time and dedication. But eliminating the fire and shock risks provides invaluable safety and peace of mind.