How to Install Knob and Tube Wiring

What is Knob and Tube Wiring?

Knob and tube (K&T) wiring was an early standardized method of electrical wiring used in buildings in Canada and the United States from about 1880 to the 1940s. It consisted of single insulated copper conductors run within wall cavities, passing through joists and studs. Porcelain knobs mounted on the framing supported the wires along straight sections while porcelain tubes protected wires where they passed through framing members.

K&T wiring has largely been replaced by newer types of insulated home electrical wiring, including non-metallic sheathed cables and plastic insulated wires, due to the substantial improvements in electrical safety. However, some older homes still contain functioning knob and tube circuits.

Reasons to Install New K&T Wiring

There are a few reasons why you may need or want to install new knob and tube wiring today:

In most cases, installing new K&T wiring is not recommended due to safety concerns and code restrictions. Always consult local building codes before beginning any electrical project.

Dangers and Downsides of Knob and Tube Wiring

While K&T wiring was a major improvement over previous wiring methods when initially introduced, it has some drawbacks compared to modern electrical systems:

Planning Your K&T Wiring Project

If you've decided to take on a new knob and tube wiring installation, careful planning is required:

Step-by-Step Knob and Tube Wiring Installation

Once your project is thoroughly planned out, you're ready to install new K&T wiring:

Gather Supplies

You'll need the following tools and materials:

Mount the Knobs

  1. Measure and mark knob positions in the framing cavities, spaced according to code requirements (typically every 4 to 5 feet).

  2. Predrill holes slightly smaller than the knob shanks. This allows a tight, secure fit when hammering them in.

  3. Use a hammer to insert the knob shanks into the predrilled holes. Leave the wired portion exposed within the cavity.

Install the Tubes

  1. Measure and mark tube locations where wiring must pass through framing members.

  2. Chisel a channel into the framing for each tube, aligned with the wire path. Make it slightly wider than the tube diameter.

  3. Fit the tubes into the channels. They should seat firmly without needing fasteners.

Run and Connect the Wires

  1. Use the knobs and tubes to guide and support the wire through the planned path. Leave some slack.

  2. At connection points, strip the ends using a wire stripper and attach wiring to devices or splices.

  3. Verify safe and secure connections by gently tugging the wires. Poor connections can arc and overheat.

Inspect and Test the Circuits

  1. Visually inspect all wiring for damage before energizing the circuit.

  2. Turn on the power and use a multimeter to test voltage and polarity at outlets and devices.

  3. Check for secure connections by wiggling splices and fittings. Faulty joints may need to be redone.

  4. Fix any issues found before putting the system into service.

Safety Tips

Replacing original knob and tube wiring requires knowledge, skill, and scrupulous attention to safety. Always consult the appropriate electrical codes and wiring standards for your region before attempting any installations. Hiring a professional electrician is highly recommended.