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:
- Individual hot and neutral wires run through porcelain knobs and tubes
- No ground wire
- Wires are surrounded by air rather than bundled in a cable
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:
-
Fire hazard - insulation on the wires can become brittle and crack over time, exposing the conductor. This can lead to short circuits and fires.
-
Shock hazard - no ground wire means there is no path for fault currents to travel. This increases the risk of electrical shock.
-
Overloading - knob and tube wiring was not designed to handle the power demands of modern appliances and electronics. This can lead to overheated wires.
-
Unsafe splices - DIY repairs may lead to improper and dangerous connections.
-
Damage - old, cracked porcelain knobs can break easily. Vermin may also chew through the outdated insulation.
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:
Don't:
- Attempt to replace knob and tube wiring yourself unless you are a licensed electrician.
- Install modern wiring next to old knob and tube wiring in the same wall cavity.
- Overload circuits with high wattage appliances and electronics.
- Bury splices in attics or walls. All connections must remain visible.
- Use insulation that could trap heat around old wiring.
Do:
- Have repairs and upgrades done by a qualified electrician.
- Completely replace knob and tube wiring whenever possible.
- Use the proper size wire with a sufficient amperage rating for replacement wiring.
- Install GFCI outlets if replacing receptacles on old circuits.
- Consider having circuits with old wiring upgraded to include a ground wire.
- Keep all wiring connections visible and accessible.
In addition:
- Inspect for signs of insulation damage, heat damage, and loose connections.
- Limit loads on outdated wiring to prevent overheating.
- Shut off power at the main panel before doing any work.
- Disconnect appliances before repairing splices.
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:
- Exposed wire conductors
- Signs of charring or burning
- Frequent blown fuses or tripped breakers
- Lights flickering or dimming
- Buzzing, sizzling, or humming from outlets
- Warm or melted plugs and outlets
-
Odd odors like burning plastic
-
Visible sparks inside outlets
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.
Conclusion
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.