A Guide to Knob and Tube Wiring

knob and tube

If your facility was built before 1950 and has never received a wire upgrade, you more than likely have knob and tube wiring in your place of operations. Knob and tube (also known as K&T) was a popular method of electrical wiring in buildings and homes in North America between 1880-1940s.

In the present day, this old fashioned form of wiring is considered obsolete and can be a hazard if left in poor condition for too long. For more, check out our guide to knob and tube wiring below!

What Is Knob and Tube Wiring?

Knob and Tube wiring uses insulated copper conductors that are passed through drilled holes in wood framing by way of insulating porcelain tubing. They are held up along their length by secured porcelain knobs, hence the name. When pulled through walls or installed in devices, such as light switches, these wires are protected by rubber insulation or flexible cloth to keep them from being damaged.

The major difference between K&T wiring vs modern wiring is that K&T doesn’t actually feature a ground wire, meaning it won’t accommodate devices with 3-pronged plugs. Additionally, modern wiring uses plastic to insulate, whereas K&T uses rubber, which is prone to wear and often requires replacement.

Dangers of Knob and Tube Wiring

Despite the stigma surrounding K&T, this older form of wiring isn’t inherently dangerous, at least when it’s in good condition. In situations where your knob and tube wiring is worn or damaged, however, you may be at risk for greater problems in the near future and could end up needing to replace.

Some instances that could cause problems with K&T wiring include:

Improper Insulation Knob and Tube Wiring

Improper Insulation

In some cases, insulation in a building may have actually been installed around the knob and tube wiring, which creates a major risk of fire. These wires heat up when electric current is passing through them, so imagine how dangerous having flammable materials surrounding this setup can be.

Poor Installation or Alterations

A lot of issues with K&T can be found with how it was installed or altered. With older systems like this, people sometimes lack the appropriate parts associated with the system to properly fix or implement them, meaning they turned to makeshift solutions that could be dangerous.


Knob and tube wiring was used in a time when businesses and homes featured very little in the way of electronic devices and appliances, so power demands were substantially lower. Now, with computers, advanced machinery, and other power consuming devices, K&T wiring struggles to keep up with demand and can easily overheat.


If the porcelain tubing cracks or the insulation flakes off, the wiring may end up fraying or sagging over time, which can lead to exposed live wires and a serious risk of fire.

If you have knob and tube wiring installed in your business, it’s important to have it inspected for signs of wear and tear by a licensed electrician. Never assume there’s no problems with the wiring just because no major visible problems have occurred.

Safety Tips for Maintaining Knob and Tube Wiring

  • Monitor how many appliances or devices are being powered in the building and don’t overextend K&T wiring’s capabilities.
  • Replace your standard power outlets with GFCI outlets featuring a reset button. Ground Fault Circuit Interrupter outlets help prevent electrocution by cutting power at the first sign of shock, thus preventing injury.
  • Have your knob and tube wiring inspected by a professional electrician and have regular wiring maintenance carried out as needed. Never try to DIY your electrical!

Can You Ground Knob and Tube Wiring?

The short answer to this is No. Due to building codes and general safety concerns, you won’t be able to have your existing knob and tube wiring grounded.

If your facility requires updated wiring, you will need to rewire the entire building to safely bring it up to date.

How Long Does Knob and Tube Wiring Last?

The copper wiring used in knob and tube wiring can last an incredibly long time, even up to 100 years! The insulation, on the other hand, doesn’t have quite the same lifespan since it often becomes brittle over time and can break with ease.

This wear and tear is one of the main reasons why K&T wiring ends up needing to be replaced.

Cost of Replacing Knob and Tube Wiring

The cost of replacing knob and tube wiring comes down to several factors, including building size, age, and accessibility to wiring.

Consulting a licensed electrician who can inspect the conditions of your setup is the fastest, most effective way to determine price.

Looking for an Electrician?

Need a professional electrician to take your wiring out of the stone age and into the modern world? Tapps Electric is your go-to for upgrades, installations, replacements, and more! Request a quote on our website or give us a call today at (253) 344-4622.

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