Introduction
Knob and tube wiring was commonly installed in homes and buildings from about 1880 through the 1930s. This antiquated system uses insulated wires run through open air, passing through knobs fastened to framing and tubes installed through holes drilled in framing.
While knob and tube wiring has lasted remarkably long in many buildings, it can become a fire and safety hazard if left untouched for decades. Frayed wires, overloaded circuits, improper splicing, degraded insulation materials, and other issues can develop over time.
As the owner or manager of a building with original knob and tube wiring, it's important to understand when and how to troubleshoot this antiquated system. Proactively identifying and addressing problems can help avoid fires or other damage.
In this article, I'll provide an in-depth guide on troubleshooting knob and tube wiring, covering key topics like:
Signs of Problems in Knob and Tube Wiring
Some clear signs indicate your antiquated wiring system may be experiencing issues:
Frequent Tripped Circuit Breakers or Blown Fuses
- Overloaded circuits straining the old wires will trip breakers or blow fuses.
- This is a warning sign of deteriorating insulation or undersized wiring for modern electric loads.
Flickering or Dimming Lights
- Lights flickering or dimming when other devices turn on suggest low voltage from resistance on the wires.
Discolored Outlets or Switch Plates
- Heat damage causes discoloration on outlets/switches.
Buzzing, Crackling, or Sizzling Noises
- These noises coming from outlets indicate arcing and dangerous sparking where wiring insulation has degraded.
Warm Outlets
- Outlets that are warm to the touch signal high resistance and excessive power draw through the wires.
Melting Insulation
- You may see melted insulation dripping out of outlets or switches if wiring severely overheats.
Blown Fuses or Tripped GFCIs When It Rains
- Moisture seeping into degraded insulation can cause short circuits when wet.
Testing Knob and Tube Wiring
If you notice any signs of trouble, testing can help identify specific problems:
Visual Inspection
- Closely inspect visible wiring for cracked, frayed or brittle insulation.
- Look for poorly spliced connections rigged together or wired improperly.
- Watch for signs of overheating like discolored wires or melted insulation.
Voltage Drop Testing
- Use a digital low impedance multimeter to measure voltage at outlets.
- Check voltage again at the circuit breaker panel and compare the readings.
- A drop of more than 3 volts indicates high resistance on long wire runs.
Insulation Resistance Testing
- Use a megohmmeter to measure resistance between hot wires and neutral/ground wires.
- Resistance lower than 1 megohm indicates degraded insulation.
Load Testing
- Run high wattage appliances like a heater or microwave at once.
- Listen and watch for lights dimming, flickering, or other issues.
- This stresses the wiring to detect if it can handle modern electric loads.
Improving Safety of Knob and Tube Wiring
If testing reveals hazards in your antiquated wiring, here are some tips to improve safety:
Replace Dangerous Wiring
- In severe cases, replacement provides the highest level of safety.
- Prioritize circuits supplying critical areas like kitchens and bathrooms.
Avoid Overloading Circuits
- Use heavier duty extension cords temporarily if needed to avoid overload.
- Plug high wattage appliances into outlets fed by newer wiring if possible.
Add GFCI Outlets
- Install GFCI outlets or breakers to protect from electrocution if moisture seeps in.
Label Inactive Wires
- Safely cap unused dead wires and label them clearly as inactive.
Address Improper Splices
- Rewire or remove any improper DIY taping, twisting, or splicing.
Clean Exposed Wiring
- Use a gentle cleaner to wipe dirt off old dry knob and tube wiring to prevent further degradation.
When to Arrange Repairs by a Licensed Electrician
While I can perform basic troubleshooting myself, it's safest to have licensed electricians handle any major repairs or comprehensive replacement of old knob and tube wiring.
Consult professional electricians immediately if you encounter:
- Any signs of fire damage like charring.
- Significant moisture damage to wiring.
- Numerous malfunctioning outlets/lights.
- High voltage drop affecting large sections of wiring.
- Extreme overheating of wires and insulation.
They have the proper tools and training to inspect and fix hazards stemming from antiquated electrical systems. Safety should be the top priority.
Conclusion
While knob and tube wiring served homes and buildings well for decades, it does have a finite lifespan. Careful troubleshooting and maintenance are key to keeping this antiquated system safe. Address any warning signs proactively before small problems escalate into fires or other major hazards. With diligence and help from skilled electricians when needed, decades-old wiring can function safely and reliably. Let me know if you have any other questions!