I recently learned about an old electrical wiring method called knob-and-tube that could potentially save me thousands of dollars on rewiring costs in my old house. As a homeowner with an outdated electrical system, I was intrigued to learn more.
What is Knob-and-Tube Wiring?
Knob-and-tube (K&T) is an early standardized method of electrical wiring used from about 1880 to the 1940s. It consists of insulated copper conductors passing through ceramic knobs mounted on wood framing and supported by porcelain tube insulators where wires enter electrical boxes.
This old-fashioned wiring system has some key advantages:
- Open air design dissipates heat efficiently
- Ceramic and porcelain are more fire-resistant than modern PVC insulation
- Wires are not bundled together so one hot wire cannot overheat others
Surprisingly, K&T wiring can still be serviceable and safe when properly maintained.
Why Rewiring is Often Recommended
Many electricians and inspectors automatically condemn K&T wiring and recommend full rewiring with modern NM cable (Romex) instead. Their concerns are understandable:
- Insulation dries out over time, allowing shorts
- Materials become brittle with age
- Alterations can compromise safety
- No ground wire for shock protection
- Inadequate for modern loads
However, rewiring a whole house with Romex can cost tens of thousands of dollars. Determining if K&T can be serviced safely could save me a lot of money.
Evaluating Your Existing Knob-and-Tube Wiring
Here are some steps I plan to take to evaluate the K&T wiring in my house:
- Check for hot spots or scorch marks indicating faults
- Look for cracked insulators or damaged wiring
- Verify proper separation between hot and neutral wires
- Plug high-draw appliances like space heaters into each circuit
- Turn on all lights and outlets to check for tripped breakers
- Consider having an electrician do load testing
- Use a megohmmeter to test insulation resistance. Lower than 1 megohm could indicate problems
- Remove any splices exposed in attics or wall cavities
- Properly terminate wires in covered electrical boxes
Making Knob-and-Tube Wiring Safer
If the K&T wiring checks out, there are some upgrades I can make to improve safety:
- Add GFCI outlets for shock protection
- Upgrade the electrical panel if needed for capacity
- Have an electrician install a grounding retrofit system
- Use arc fault circuit interrupters (AFCIs) to prevent fires
- Isolate high-draw circuits like kitchen or laundry on modern wiring
Properly maintained K&T can be reasonably safe for continued use. I plan to have a licensed electrician assess my system to see if targeted upgrades could save me the major expense of rewiring the whole house. With the right approach, this forgotten wiring method could really pay off!