How to Troubleshoot Your Building’s Antiquated Knob and Tube Wiring


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

Flickering or Dimming Lights

Discolored Outlets or Switch Plates

Buzzing, Crackling, or Sizzling Noises

Warm Outlets

Melting Insulation

Blown Fuses or Tripped GFCIs When It Rains

Testing Knob and Tube Wiring

If you notice any signs of trouble, testing can help identify specific problems:

Visual Inspection

Voltage Drop Testing

Insulation Resistance Testing

Load Testing

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

Avoid Overloading Circuits

Add GFCI Outlets

Label Inactive Wires

Address Improper Splices

Clean Exposed Wiring

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:

They have the proper tools and training to inspect and fix hazards stemming from antiquated electrical systems. Safety should be the top priority.


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!