How to Troubleshoot Old Knob and Tube Wiring

How to Troubleshoot Old Knob and Tube Wiring


As a homeowner with an older house that still has original knob and tube wiring, I know how frustrating and potentially dangerous this outdated system can be. Properly troubleshooting and addressing issues with knob and tube wiring requires knowledge, patience, and care. In this guide, I will share what I've learned about troubleshooting common problems and determining the best solutions for updating old knob and tube wiring.

Understanding Knob and Tube Wiring

Knob and tube wiring was commonly installed in homes built before 1950. This type of wiring consists of:

The wiring is routed throughout the house with the knobs keeping the wires separated and the tubes protecting where wires pass through open stud bays.

While knob and tube was suitable for smaller electrical loads of the past, it can be problematic and unsafe for modern power usage. Key issues include:

Now that we've reviewed the basics of knob and tube wiring, let's look at troubleshooting common issues.

Signs of Problems with Knob and Tube Wiring

There are several signs that can indicate issues with old knob and tube wiring:

Any of these signs mean it's time to thoroughly inspect the wiring and make needed repairs.

Testing Knob and Tube Wiring

Here are some steps I take to test and troubleshoot my knob and tube wiring:

Visual Inspection

Continuity Test

Load Test


Prioritizing Repairs

Once I've identified any problems through testing, I determine repair priorities as follows:

I focus on any immediate fire and shock hazards first. Smaller issues may be managed by replacing fuses, adding circuits, or installing GFCIs until more extensive repairs can be made.

Upgrading from Knob and Tube Wiring

When issues become too persistent and repairs too costly, upgrading the wiring is the best solution. Here are my top options:

Rewiring the whole home and removing all old knob and tube can be very costly. I got estimates from $8,000 to $15,000 for a full rewire of my 1,200 sq. ft. house. Running new wires or installing subpanels to add grounded circuits is a more affordable interim option.

Key Takeaways

Troubleshooting and repairing knob and tube wiring requires knowledge of the system, careful inspection, and testing. Prioritize immediate safety hazards first, then consider upgrades to provide modern, grounded wiring. With some effort and diligence, you can keep old wiring in reasonable shape and determine the best long-term solutions when problems persist. Hiring a professional electrician is advisable for major repairs or upgrades.