What is Knob and Tube Wiring?

Knob and tube wiring was commonly installed in homes built before 1950. It consists of individual hot and neutral wires that are run through porcelain knobs and tubes.

The hot and neutral wires are separated by air space rather than being bundled together in a cable. This type of wiring does not include a ground wire.

Key features of knob and tube wiring:

While knob and tube wiring was safe when it was installed correctly, it can become hazardous as it ages. Repairing it requires special consideration to avoid risks.

Dangers of Old Knob and Tube Wiring

There are several potential dangers associated with old or damaged knob and tube wiring:

Any of these hazards mean knob and tube wiring must be repaired or replaced as soon as possible. But this should be done with care to avoid making the problems worse.

Dos and Don'ts For Repairing Knob and Tube Wiring

If you have knob and tube wiring, here are some important dos and don'ts to keep in mind:



In addition:

Carefully following precautions and best practices will help ensure your knob and tube wiring repairs are completed safely.

Step-By-Step Guide for Safe Repairs

If you must attempt to repair minor issues with knob and tube wiring yourself, here are some steps to follow:

1. Turn off power

Shut off power to the circuit at the main electrical panel before doing anything else. Remember to double check that power is off with a non-contact voltage tester.

2. Inspect for damage

Visually inspect the wiring for cracked, brittle, or damaged insulation. Also look for loose connections, gaps in the wire path, or places where insulation is missing. These indicate points that need repair.

3. Splice and insulate worn sections

DO NOT directly replace old copper wiring. The new copper can accelerate corrosion. Instead, splice worn sections by connecting new wiring on either end. Use wire nuts, proper splicing techniques, and electrical tape for a secure connection.

4. Support and stabilize components

Resecure any loose knobs, tubes, splices, and connections. Broken or cracked porcelain pieces should be replaced. Fill any gaps in the path that wiring runs through.

5. Add GFCI outlets

For added protection, replace regular receptacles with GFCI outlets. These will provide ground fault protection by shutting off power in the event of a short.

6. Improve accessibility

Leave all splices, taps, and terminals uncovered and visible. Do not bury them in attics or walls. Accessibility allows for ongoing inspection.

Once you have completed repairs, turn power back on and carefully test each outlet and light fixture serviced by the wiring. Check for proper function and no signs of sparks or overheating.

When to Call an Electrician

While limited repairs can safely be done by a homeowner, it is best to have knob and tube wiring evaluated and upgraded by a qualified electrician. They have the expertise to fully assess risks and design an appropriate repair or replacement solution.

Call an electrician immediately if you see any of the following:

These are signs of serious hazards like short circuits. Continuing to use knob and tube wiring in this condition puts your home at high risk of fire.


Repairing old knob and tube wiring must be done carefully and correctly to prevent creating new risks. In many cases, complete replacement is the best option to protect your home and family from fire and shock hazards.

Pay close attention to warning signs and consider having an expert assess your outdated wiring. With the right precautions, you can avoid the dangers of DIY knob and tube wiring repairs.